December 1, 2022 • 59 mins
Nicole Yunger Halpern reenvisions 19th-century thermodynamics for the 21st century, using the mathematical toolkit of quantum information theory. She is a fellow of the Joint Center for Quantum Information and Computer Science (QuICS), a theoretical physicist at the National Institute of Standards and Technology (NIST), and an Adjunct Assistant Professor at the University of Maryland. She is also the author of Quantum Steampunk: The Physics of Yesterday’s Tomorrow, a book that blends the topic of quantum thermodynamics with the steampunk genre of art and literature, juxtaposing a Victorian aesthetic with futuristic technologies. She tells co-hosts Lauren and Colin about the inspirations behind her work – scientific and artistic – and explains how fundamental ideas in quantum information theory are reshaping science and technology. View the episode transcript here.
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Conversations at the Perimeter is co-hosted by Perimeter Teaching Faculty member Lauren Hayward and journalist-turned-science communicator Colin Hunter. In each episode, they chat with a guest scientist about their research, the challenges they encounter, and the drive that keeps them searching for answers.
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(00:00):
(upbeat music)
- Hello, everyone, and welcome back
to Conversations at the Perimeter.
On this episode, Lauren and I chat
with Nicole Yunger Halpern.
She is a quantum thermodynamicist,
which is just about ascomplicated as it sounds,
(00:21):
but thankfully Nicole isgifted at explaining it,
and she's done so in thecontext of steampunk,
the science fiction genre
that is sort of set inthe Industrial Revolution.
And she's the author ofthe book by that title,
"Quantum Steampunk (00:34):
The Physics of Yesterday's Tomorrow."
- I always really lovetalking to physicists
who work at the intersectionof different fields,
so it was really fun to talk to Nicole
and get to hear about her work
at the intersection of quantum physics,
information science, and thermodynamics.
Nicole joined us for this recording
when she was visiting PerimeterInstitute for a conference,
(00:56):
but she also shared abouther times at Perimeter back
when she was a student within
the Perimeter ScholarsInternational master's program,
which I also work in as ateaching faculty member.
- So without further ado,
let's dive into the worldof "Quantum Steampunk"
with Nicole Yunger Halpern.
(upbeat music)
Nicole, thank you so much for being here,
(01:16):
and welcome back to Perimeter Institute.
- Thank you. It's reallya pleasure to be here.
Thanks for having me on the podcast.
- I've just finished reading your book,
The Physics of Yesterday's Tomorrow,"
and we're so keen to talk to you about it
because the ideas of quantum
and steampunk I've never heardcombined this way before.
And I honestly have never read a book
(01:38):
about thermodynamics before,
certainly not quantum thermodynamics.
So I'm hoping you can take our audience
on a little bit of a backward journey.
And what's meant by theterm "thermodynamics,"
and is it as scary as Ialways thought it was?
- I would say it's not as scary.
The thermodynamics issimply the study of energy,
the different forms that energy can be in
(01:59):
and the possible transformationsamongst those forms.
The theory of thermodynamicswas developed during the 1800s.
It was inspired by theIndustrial Revolution.
For the first time,
steam engines were being usedon a large scale in industry,
and people wanted to figure out
how efficiently they could operate.
So they gave thermodynamicsthis practical bent,
(02:19):
thinking about powering factories
and cooling systems down,
and nowadays, also charging batteries.
So thermodynamics hasthis practical viewpoint,
but it's also become very foundational.
This is a side of it that I really love.
In thermodynamics, we end up thinking
about questions like why time flows
(02:41):
in only one direction.
And the thermodynamicistsof the late 1800s also got
to wrestle with fundamentalquestions about atomism.
So the theory of atoms hadn'tbeen entirely well accepted
by the Victorian era.
So people were debating about
to what extent its useful
or scientific to talk about tiny particles
(03:02):
that no one can even see.
Thermodynamics appeals to me in part
because of this fundamentalspirit that it has.
And as you mentioned,
I also see its modern incarnation,quantum thermodynamics,
as sharing its aesthetic with steampunk.
Steampunk is a genre ofliterature, art, and film.
(03:24):
Steampunk stories take placeduring the Victorian era.
There are settings such as greedy,
nighttime, dangerous London Streets,
Sherlock Holmes in London, Meiji Japan,
and the Wild wild West.
In these settings arefuturistic technologies,
such as time machines, thedirigibles, and at automata.
(03:49):
There's this beautifulblend of old and new
that creates both a sense of nostalgia
and a sense of adventureand exploration and romance.
In my field, which is at the intersection
of quantum information and thermodynamics,
we're taking the theory ofthermodynamics from the 1800s,
(04:10):
which was built forlarge, classical systems,
such as steam engines.- Like steam engines.
That is quite right.- Exactly.
- I always think of theIndustrial Revolution
and thermodynamics, Ithink of steam trains.
- Exactly.
Nowadays, experimentalistshave great control
over quantum systems,
and the cutting edge technology of the day
is not so much the steam engine,
but cutting edge technologiesinclude quantum devices,
(04:33):
such as quantum computersand quantum sensors.
But we need to take thistheory of thermodynamics
from the 1800s and extend it
and really re-envisionit for the 21st century.
In the first place,
how do the thermodynamic laws still hold
for quantum systems?
How can we reformulatethem for quantum systems
(04:53):
and how they encode and interplay
between energy and information,
especially quantum information?
Also, we know from thequantum information revolution
that quantum phenomena,such as entanglements,
can enhance information processing tasks,
such as certain computations.
Just as there areinformation processing tasks,
(05:14):
there are thermodynamic tasks,
such as charging batteriesand powering cars.
So given that quantum phenomena
can enhance information processing tasks,
can they enhance thermodynamic tasks?
In this intersectionof quantum information
and thermodynamics, wehave, on the one hand,
the thermodynamic theoryof the Victorian era,
and on the other hand,
(05:36):
the futuristic technologiesof quantum computing
and the cutting edge scienceof quantum information theory.
I see this fusion of old and new
as sharing its aesthetic with steampunk.
- When I think of quantum thermodynamics,
the very first simple image
that popped into my head was avery, very small steam train.
And I know that's not right.
(05:56):
Can you tell us what's meant more broadly
by the term "quantum?"
What does quantum describe,
and how does it connect to thermodynamics?
- I think of quantum physics
as very loosely beingthe physics of the small.
What we mean by smallcan depend on context.
If you have a lot of particles
that are crammed into space small enough
that they interact very strongly,
(06:17):
then that space might beas large as New York City.
In which case, the particles
that are crammed very closelytogether form a black hole.
Quantum physics isrelevant to black holes,
even though black holes seem large
in the sense that NewYork City seems large.
But the particles arecrammed so close together
that they interact very strongly,
so we can't describe them
(06:38):
with just the physicsfrom before the 1920s.
That's how I think of quantum.
You also mentioned the possibilityof quantum steam trains.
Quantum engines have been developed.
They've been designed by theorists
and now realized experimentally.
It turns out that quantum engine can be
as small as a single atom.
(06:58):
That was the basis forthe first quantum engine
that was proposed in 1959,
and then in more detail in 1967.
- So I have to tell you, Nicole,
I actually have some cousinswho listen to this show,
and they work as mechanics for aircraft
and specialized vehicles.
And I was particularlyexcited to talk to you today
because I think that you could allow me
(07:20):
to learn a bit more aboutsomething that they do.
So can you actually tell usreally what an engine is?
- We could focus on a heat engine
since that's a simpleand canonical example.
And in particular, a heatengine that's some device
that has access to twodifferent environments
at two different temperatures.
(07:41):
Heat naturally flows fromhot systems to cold systems.
And an engine is a device
that takes some of thisheat that is flowing
and turns it into work.
Heats and work are the two different types
of energy that can betransmitted between objects.
Heat is random energy. It's uncoordinated.
(08:01):
It's the energy of particlesjiggling all about.
Work is organized, coordinated energy
that can be directly harnessed
to do something usefullike push a rock up a hill.
So a heat engine uses thisdifference between temperatures
and takes the random heats
and transforms it into useful work
(08:23):
while not changing itself very much.
- And what is the quantum version of that,
the relationship between heat and work?
- What is quantum heat
and what is quantum workare some of the fundamental
and trickiest questionsof quantum thermodynamics.
(08:43):
I gave some intuition about what heats
and work are in classical thermodynamics.
We can take those intuitions
and try to apply them to quantum systems,
but here's a simpleexample of why defining
or conceiving of quantumheat and work is tricky.
Suppose that we want to measure
(09:03):
how much heat a system absorbs.
We can measure its energy,
then let the system absorb the heats,
and then measure the energy again.
The amount of energy it has
at the end minus the amount of energy
that it has at the beginningis the heat absorbed.
But suppose that we try thisprocess on a quantum system.
(09:24):
If we measure a quantumsystem, we disturb it.
And if we measure aquantum system's energy,
we actually change its energy.
So by trying to measure the heat
or work absorbed by a quantum system,
we can change the amount of heat
or work absorbed by the system.
- And that doesn't happenin the classical sense.
That's only when you'redealing with quantum particles.
- Right.
So we have to think about quantum work
(09:46):
and heat totally differently.
There's a whole spread
of different definitions of quantum heat
and quantum work thatdifferent people have proposed.
I think of it as a menagerie.
So every time I find a new paper
with a new definition ofquantum heat and work,
I add it to this filethat I call menagerie
of quantum heat and work.
(10:06):
I think of the definitions
as different species in the menagerie.
I think that differentdefinitions of quantum heat
and work are useful in different contexts.
There is a very well-known trend
in theoretical physics to unify,
to put different definitions
and theories and ideas together
to make some one unified theory,
(10:28):
especially at the Perimeter Institute.
However, I think that
in this very operationaltheory of thermodynamics,
where we're really thinking about agents
who are given some resources,
like environments atdifferent temperatures,
they're trying to perform taskslike a refrigerator system,
it can be useful to define heat
and work in terms of whatsort of a system we have
(10:51):
and, in particular, what we can do to it.
How we can perform work on it,
how we can poke it, how we can measure it.
What systems we havearound, like batteries,
that they can interact with.
- I love that in your bookyou provide some really sort
of straightforward examples,
including beautiful illustrations,
which I want to talk about too.
But the examples, a lot of theminvolve a particle in a box.
(11:13):
And it's so simple.
I'd never thought of thermodynamics
as being something that you could explain
with particles in boxes.
Can you tell us why that's such a sort
of standard explanation thatyou go back to frequently?
- We very often think
in thermodynamics about gas in a box.
It's quite possible thatmany listeners learned
(11:35):
in chemistry class in high school
about ideal gases, their idealizations.
They have very simple properties,
though they're described
by pretty simple equations, in many cases,
but they exhibit reallyinteresting phenomena,
such as they provide great examples
of the second law of thermodynamics,
(11:55):
which explains or helps usunderstand why time flows.
They have properties like volume
and pressure that are measurable.
And by thinking about howthe particles are acting on,
say, the walls of their boxes,
beating against the boxes' walls.
We can think of what pressure even means.
This is a great playground
for understanding thermodynamicquantities like pressure
(12:16):
and volume and entropy.
Also, in quantum theorywe like thinking a lot
about particles in boxes.
Very often we think aboutsingle particles in boxes.
So in the book, there are some examples
of really, really evenmore idealized simple gases
that consist even of single particles.
- And can you take usback to how you combined
(12:38):
or blended these ideas of thermodynamics
and quantum mechanics and steampunk?
Like, where did that come from?
How did you make those connections?
- That's a good question.
I encountered some steampunkworks as I was growing up.
For instance, I loved the book series
the "Chronicles of Chrestomanci"by Diana Wynne Jones.
(12:59):
She was a wonderful andaward-winning fiction writer,
one of the best sciencefiction fantasy writers
of the 20th century, notjust according to me,
but also authors thatlisteners might know,
like Neil Gaiman.
I encountered her worksand Philip Pullman's works.
I didn't realize, though,that steampunk was a genre.
I didn't quite recognize whatit was that I was reading.
(13:22):
I didn't recognize thatthere was some unifying idea
across these works.
Then, at the beginning of grad school,
somehow I discovered thatsteampunk was a genre.
By then, I had come to this intersection
of quantum information and thermodynamics,
and I suddenly just realizedthat it has the aesthetic
and the spirit of steampunk.
(13:43):
I was so delighted to findthis shared connection
between the hardcorephysics that I was doing
and the genre ofliterature, art, and film.
I wrote a blog post about it right
at the beginning of my PhD.
I blogged for Caltech's Quantum Institute.
Then the idea started developing.
It ended up the title of my PhD thesis,
(14:05):
and then the name of myresearch group in Maryland,
and then I wrote a book.
- You mentioned grad school.
That was here at Perimeter, right?
- I earned my master's
at the Perimeter ScholarsInternational Program.
Then I was at Caltech for my PhD.
- And I remember reading, I believe,
in the book that it was atthe Waterloo Public Library,
which is just across the street,
(14:26):
that you came across a bookthat had steampunk elements.
Can you tell us what you found
in that book that inspired you?
- During most of my year in PSI,
Perimeter Scholars International,
I was in the Perimeter library working
something like 12 hours a day.
So I didn't have time to go tothe Waterloo Public Library.
(14:46):
But in the spring, classes ended,
and so I finally had a few free hours.
And I explored theWaterloo Public Library.
I found a novel by the Canadianpoet Jay Ruzesky called
"The Wolsenburg Clock."
It is about an old, old clock in Austria.
The author constructs this story showing
(15:07):
how the clock is affected by
and affects different people
in this town throughout the centuries.
One of the scenes takesplace during the 1800s.
An inventor is about to clean up the clock
and redesign it
and really invest it withthe spirit of what he does,
(15:30):
which is build automata.
So there's a scene in which he is standing
on a balcony gazing down at a ballroom
that he's converted into his workshop.
His children and wife
and so on are buildingclockwork-driven elephants
and snakes and snake charmers.
And he has this coat onthat billows out behind him.
(15:51):
- He sounds very steampunk.
- Exactly. That scene stuck in my mind.
And shortly thereafter,
I realized that that scene was steampunk.
And shortly after that,
I realized that my research was too.
- So did you always know
from the time you started your PhD
that that's what you wantedto focus your thesis on?
- Yes.
During the end of my undergrad years,
(16:14):
I increasingly found my way
to quantum information theory,
and I asked professorsin my physics department
who does the kind ofquantum information theory
that I'm interested in.
It was an abstract mathematical flavor.
They pointed me to some webpages
(16:34):
of some faculty members across the world.
I increasingly honed in on phrases
and ideas that really spoke to me.
I found that they wereat this intersection
of quantum informationtheory and thermodynamics,
where people are thinkingabout uncertainty
and entropies and information
and energy in a fundamental way.
(16:55):
Shortly thereafter, I came to Perimeter.
I had the wonderful good fortune
to work for my final project
with someone who was apostdoc here at the time,
Markus Muller, and Robert Spekkens,
who's a faculty member here.
We worked on a topicin quantum information,
theoretic thermodynamics.
(17:15):
At the end of the project,we said to each other,
"Okay, so now we've gained this toolkit.
What shall we do with it?"
I came up with a project,
and that was the first project in my PhD.
There was always another project
and more collaborators to reach out to.
- Since we're asking youabout your PhD right now,
as part of this show,
we collect questions fromsome of our listeners.
(17:37):
And a current PSI studenthere named Anna Knorr sent
in a question about your thesis.
- In your thesis, youwrite, "Steampunks dream it,
Quantum informationthermodynamicists live it."
Is that simply a cool slogan,
or does it truly motivate you
and drive you in your research?
(18:00):
- Steampunk is a genre ofscience fiction and fantasy.
It is seen as something that isn't true.
However, I do believe that it is coming
to life in the intersection
of quantum informationtheory and thermodynamics.
Thermodynamics wasdeveloped during the 1800s.
(18:21):
We carry a bit of theVictorian era with us
when we're doing thermodynamics.
And quantum computers arefuturistic technologies.
We're still building them.
And quantum information theoryis cutting edge science.
So I do believe that quantuminformation thermodynamicists
really are living what
until now has been seenas a fiction, steampunk.
(18:44):
- And in a lot of whatyou've been talking about,
you've been saying your work is really
at an intersection of several fields,
one of which is information science.
And I'm wondering if you can talk
a little bit more about information.
I know in your book you say
that we live in an information age.
So can you tell us a littlebit about why you said that
and maybe first just what information is?
(19:06):
- I've heard twodefinitions of information.
One that's a bit easier to explain
is information is the ability
to distinguish between alternatives
or a necessary ingredient
for distinguishing between alternatives.
For instance, when youget up in the morning
and need to figure out what to wear,
you need to know what the weather is like.
(19:27):
So you peer through the window, perhaps,
and see that there's sun or there's rain.
When you've peered through the window,
you've gained information.
You've been surprised.
So information is thatwhich gives us the ability
to distinguish whetherit's sunny or rainy.
- And is information itself thermodynamic?
(19:48):
Does information have anenergy component to it,
or does quantum informationhave an energy component to it?
- Information plays arole in thermodynamics.
For instance, in my book,
I walk through some examples that show
that we can use informationto turn heats into work.
(20:10):
We said that heat is random,uncoordinated energy,
and work is coordinatedenergy that's directly useful.
If we have information,
then we can run what's sometimes called
an information engine totake those random heats
and convert it into useful work.
We can also run the enginebackwards and perform work,
(20:34):
such as by draining abattery, to gain information.
There's certainly an interplay
between information and energy.
- And Nicole, when I first got your book,
the first thing I did was,of course, to flip through it
and admire the reallybeautiful illustrations
that Colin already talked about,
but when I did that,
there was one phrase that jumped out
(20:54):
to me right from the beginning.
And it's on page 19where you have a section
that's called The Liverof Information Theory.
Can you tell us a little bit about this?
- Yes.
When I was in high school,
I had a biology teacher who said,
"If you ever don't know the answer
(21:15):
to a question on a test of mine,
you should write down 'liver.'"
(Colin laughs)
The liver turns out toperform a ridiculous number
of functions in the human body.
So if you don't know theanswer to a biology question
and you answer liver,
then you have ananomalously high probability
of being correct.
Similarly, in informationtheory, if you're asked,
(21:38):
"What is the optimal efficiency
with which we can perform someinformation processing task?"
and you answer, "It'sgiven by an entropy,"
then you have an anomalouslyhigh probability being correct.
So very often in informationtheory the answer
to a question is entropy.
So I think of entropy as theliver of information theory.
(21:58):
I should also mention,
partially in response toColin's recent question,
that entropy is a manifestation
of information in thermodynamics.
Entropy is a measure of uncertainty,
how little we know.
And entropy comes up even
in the second law of thermodynamics,
(22:20):
which is a very, veryfundamental statement.
- Yeah, entropy is aconcept you hear a lot
in different branchesof physics and science.
And honestly, it's one
that I have troublewrapping my head around.
I hope I'm not alone in that.
Can you give us a bit more of an idea?
What does that mean to say
that entropy sort of playsa role in information?
- First, there are manydifferent entropies,
(22:42):
and entropy is a measure of uncertainty.
At least that's how I think of it.
For instance, I recentlylived in the Boston area,
and I came to learn that the weather
in the Boston area is avery, very random variable.
On any given day, there's some probability
that the weather will be mostly sunny,
some probability thatit'll be mostly rainy,
(23:02):
some probability thatit'll be mostly cloudy,
some probability thatit'll be mostly snowing.
If on any given day youlearn what the weather is,
then you gain some amount of information,
you are surprised by some amount,
and a measure of how surprised you are
is an entropic quantity.
It depends on how probablethat weather pattern was.
(23:24):
Also, suppose that youperform this process
on many, many days.
On each of many, many days,you learn what the weather is,
and you average youruncertainty over many days.
This is another measure of uncertainty.
There are differentmeasures of uncertainty
that describe different contexts.
So there are different entropies.
I've described entropy in aninformation theoretic way.
(23:48):
We can also see how it shows up
in thermodynamics viayour favorite example
of a gas in a box.
- Mm-hmm.
- Suppose that there is some gas in a box.
It has some large-scale properties
that characterize the gas as a whole,
such as the energy of thegas, the volume of the gas,
the number of particles in the gas.
(24:09):
But we might have just this little bit of,
or, I shouldn't say bits sincethat's a technical term here
in information theory context.
Suppose that we just know thesefew large-scale properties.
We could also zoom in on the gas particles
and realize that, at any given instant,
the gas particles have some positions,
They have some momenta.
(24:29):
So they have some masses,
and they're moving with certain speeds
in certain directions.
There are many of thesemicroscopic configurations
that are consistent withone large-scale picture
of energy and volume and particle number.
If we know just thoselarge-scale properties,
then how ignorant are we
(24:51):
of the microscopic configuration?
That's a thermodynamic entropy.
- Lauren's last question reminded me
that one of my favoriteparts about your book
is the chapter titles and the subtitles.
They're are some of the mostcreative ones I've ever seen,
including How to Insult aQuantum Information Theorist.
so I'm hoping you can tell us,
how do we insult a quantuminformation theorist?
(25:13):
- Say, "Oh, quantum information theory.
Isn't that all just linear algebra?"
- So if I were a quantuminformation theorist,
why would I be insulted by that?
- I can explain with a story.
When I was an undergrad,
I took a linear algebra course,
and I was asked toexplain what I was doing.
I said, "I'm learning
(25:34):
to solve basically thesimplest equations."
These are actually the kinds of equations
that we encounter in middle school.
And in response I was told,
"And for this you had to go to college?"
(Colin laughs)
So linear algebra is a somewhatstraightforward extension
of what we learn in middle school.
Except in middle school,
we don't deal with tens
or hundreds of these equations at a time.
(25:56):
- And on the topic oftitles and subtitles,
I don't wanna risk givingaway too many spoilers
because I want people to read your book,
but the subtitle of your entire book
is The Physics of Yesterday's Tomorrow,
and this is also the titleof a chapter in your book.
Can you tell us a littlebit about this title?
- I wish I could take credit for it,
(26:17):
but my acquisitions editor
at Johns Hopkins University Press,
together with her team,
came up with this subtitle.
And as soon as I saw it,I fell in love with it.
I think of this subtitle
as embodying the ideaof quantum steampunk.
It is a branch of physics,as well as chemistry,
but it is the physicsof yesterday's tomorrow
(26:40):
in that quantum steampunk re-envisions
the Victorian era's thermodynamicsfor the 21st century.
- Because steampunk issuch a visual aesthetic,
you had an illustrator
to create these beautifuldiagrams in the book.
Can you tell us how thatcame to be and how...
I assume there's not
that many illustrators out there
(27:01):
who just know quantum thermodynamics
like the back of their hand.
How did that relationship come to be?
- The illustrator is Todd Cahill.
He's a steampunk artist,
and he actually had no experience
with quantum physics whatsoever.
So we had a lot of conversations.
I encountered him throughanother steampunk artist.
(27:22):
Couple of years ago,
the steampunk artist BruceRosenbaum reached out to me.
He had watched a talk that I had given.
I actually suspect that itwas the first colloquium
that I gave for the IQC,
the Institute for QuantumComputing, near Perimeter.
He said, "I love the spirit of this talk.
Would you like to collaborate
(27:43):
on a quantum steampunk sculpture?"
Bruce creates large, as in human size,
or even larger, interactive,
kinetic steampunk sculptures
for museums and restaurants and hotels.
I had no experience withanything like this ever before,
but it sounded likefun, so I said, "Sure."
We talked a lot about possible designs.
(28:05):
We ended up collaborating
with another artist to create a design
of a quantum engineformed from a trapped ion
with the classical counterpartof the engine on the outside.
The sculpture as a whole looks like
an armillary sphere hearkeningback to a few centuries ago.
But also, this armillarysphere is a sphere,
(28:27):
so if you show it to someonein quantum information,
they'll say, "Oh, that lookslike the Bloch sphere,"
which represents the state of a qubit,
a basic unit of quantum information.
After I started collaborating with Bruce,
I wrote this book.
And eventually, we neededto find an illustrator,
so I asked Bruce if hecould suggest anyone.
(28:48):
And he suggested Todd.
Todd was great about learningabout quantum physics
and going back and forth with me
about representing visually,in a quite beautiful way,
images that I could onlysketch in a very poor manner
'cause I have very littletraining in drawing.
- I was gonna ask if these were images
(29:08):
that you already had in your head,
or if the collaborative processwith him helped you form,
you know, how do youvisualize this stuff that is,
most of it's invisible to us?
It's at the quantum level.
- Yes.
I sketched some diagrams, but again,
I have very, very littletraining in drawing.
So I gave him my poorlittle sketches and said,
"Can you make these look steampunk?
(29:29):
Then can you add some likeflair here and there?"
And that is what he does extremely well.
So he turned my stick figure type drawings
into beautiful illustrations.
- And some of those illustrations sort
of provide explanation of what's happening
with some characters in your book.
It's a very fascinating book in the sense
(29:49):
that it's a science book kinda
with a steampunk novella woven into it,
with characters, fictional characters.
Can you tell us who those characters are
and where they came from?
- Yes.
So the book is mostly nonfiction,
but each chapter beginswith a little snippet
from a steampunk novel thatresides in my imagination.
(30:12):
There are characters in that story.
The main characters are calledAudrey, Baxter, and Caspian.
They have this nemesis, Ewart.
I enjoyed playing withthe tropes of steampunk
in what is otherwise a very serious novel
about hardcore science.
I tried out this strategywhen writing an article
(30:35):
for Scientific Americana couple of years ago.
I was asked to write an articleabout quantum steampunk,
and I thought that itwould be fun to start
with something quite different
from the hardcore sciencethat quantum steampunk is,
to start with this playfulsnippet from an imaginary novel
to illustrate what steampunk is.
So I partially wanted toillustrate what steampunk is
(30:57):
for those unfamiliar with it.
Partially, I wanted to havefun playing with these tropes,
like the very spirited,
vivacious, young girl in the Victorian era
who refuses to be pinned down
by the expectations of her society
and corsets and so on and so forth.
Also, dark, dangerous London streets.
(31:19):
It was fun to play with these ideas.
They did end up helpful later on
in the chapters toillustrate scientific ideas.
Very often in an operational theory,
like information theory, wespeak in terms of agents.
I think of an operational theory
as one that can bephrased in terms of agents
(31:41):
who have certain resources
and need to perform certain tasks,
so they try to figure outhow to perform those tasks
as efficiently as possible.
Information theory is operational.
In information theory,
we think about the tasksof compressing data,
communicating information overa noisy channel, and so on.
In thermodynamics, wethink about refrigerating
(32:03):
and charging batteries andpowering cars and so on.
Many of information theory'soperational stories are phrased
in terms of characters Alice and Bob.
They have a friend, Caspian.
Sometimes they are eavesdropped on by Eve.
So I gave the characters
in this imaginary steampunk novel names
(32:25):
that begin with the sameletters, A, B, C, and E.
- It's funny, I didn'teven put that together
until just now.
We are actually sitting
in the Alice room directlybelow the Bob room just
to demonstrate how commonlyused those terms are in science.
- Yes, very relevant.- Sorry, go on. (chuckles)
- I figured that some readers would see
that very quickly, and other readers,
say, who might come fromthe steampunk community,
(32:47):
would maybe not make the connection
between Audrey and Alice,
but instead would recognize more
of the steampunk tropesand smile at those.
I thought referring tocharacters such as Alice
and Bob is really helpfulfor explaining our science
and formalizing information theoretic
and thermodynamic tasks.
(33:08):
But we refer to Alice and Bob so much,
it would be fun to havedifferent characters.
Hence Audrey and Baxter and so on.
- I think this is justreally what makes your book
so unique, is that the steampunk
is really infused all the way throughout.
And we actually gotanother question sent in
on a related topic.
This one is from Matt Duschenes,
who's currently a PhD student
(33:29):
at the Institute for Quantum Computing
and the Perimeter Institute.
- So you found a great connection,
and we're really inspiredby the genre of steampunk
to drive your research directions.
Do you think there aremore serious opportunities
for this kind of inspiration,
and that physics as a field should look
to draw more connections with art?
- I think that
how quantum thermodynamicsshares its spirit
(33:50):
with steampunk is kind of a gift.
It makes doing the physics even more fun
because of this connection.
I think that it would be wonderful
to find more such connections
between fields of science andgenres of art and literature.
I've always enjoyed studying everything,
and I was drawn to physics in the manner
(34:11):
of a natural philosopher from,
say, the 1700s or early 1800s.
They studied, in a very rigorous sense,
aesthetics, as well as geometryand astronomy and so on.
I think that there's a lot of richness
that we can add to ourlives' interpretations
(34:33):
and understandings by engagingin interdisciplinarity.
That said, there's somethingthat's unique to physics,
and I think that to be a physicist,
one really needs to focusvery hard on the physics.
But something like steampunk
can provide extra energy and inspiration.
- Growing up, were you readingscience fiction novels,
(34:53):
or were you studying thermodynamics?
How did sort of yourformative years lead you
in this direction?
- I grew up reading justabout everything just
about all the time.
(Colin laughs)
I read while waiting to get picked up
from school in the afternoon.
I read while waiting for foodto arrive at restaurants.
(35:15):
I read on weekends. I read after school.
This reading taught me tobuild worlds in my head.
I always had characters andplots and settings in my head.
I think of my job nowas building universes
in my head for a living.
- So we've already asked youabout how you got interested
(35:37):
in the specific field ofquantum thermodynamics,
but I'm wondering if youcan also share with us
how you came to findyourself as a physicist.
- I did want to study everything,
so I resisted choosing amajor as long as possible.
- That was at Dartmouth?
- Yes, at DartmouthCollege in New Hampshire.
I had always hadphilosophical inclinations.
(35:58):
I always enjoyed engagingwith abstract ideas.
I had a philosophy teacher in high school
who was fascinated by the paradoxes
in quantum theory and relativity.
He didn't have any background in physics,
he would be the first to admit,
but he passed on to me acuriosity about these fields.
(36:21):
Meanwhile, I was absolutelyadoring my calculus class
and my physics class and so on.
I absolutely wanted tokeep studying those.
I found in the physics department a number
of faculty members who wereextremely good physicists.
I've come to appreciate that more and more
as I've become a colleague
(36:42):
and been able to look attheir works as a colleague.
They also had philosophical inclinations.
They also appreciated history.
They helped me construct a major
that was partway between the physics major
and the create your own major.
I took a bunch of physics courses,
and I took math, philosophy,
and history courses related to physics.
(37:04):
I got to call this major.
My spirit was very much in thephysics department, though.
And by the end of my undergrad experience,
I determined that it was physics
that I wanted to burrow into very deeply.
So after that, I tried outresearch as a research assistant
in Lancaster Universityin the United Kingdom.
Then I came to the Perimeter Institute.
(37:27):
And here, I had my first opportunity
to do research on the intersection
of quantum informationtheory and thermodynamics,
and I absolutely adored it.
- What did you adore about it so much?
- I love the foundational perspective.
I love the abstract ideas.
Entropy is a strange idea
and entropy-- Thank you. I thought so.
(37:49):
- And entropy is a function.
You can write down the mathematical form
of a typical entropy.
And it looks funny.
It has multiple piecesthat are kind of odd.
It has a negative sign.
It has two copies of aprobability. It has a logarithm.
There are good reasons
why this entropy hasthis mathematical form,
(38:11):
and I go through such an argument
in my book for why it makes sense,
but if you just look at it,it looks like an odd duck.
But on the other hand,
entropy lies behind thesecond law of thermodynamics,
which helps us understand why time flows.
That is so very fundamental.
This tension between thatfunny-looking function
(38:34):
and the very fundamental ideahad drawn me for a long time.
Also, as I mentioned,
I've always hadphilosophical inclinations.
I appreciated the fundamental nature
of the laws of thermodynamics
and the axioms of quantum theory.
I appreciated how quantuminformation theory sits
(38:55):
at the balance betweenthe very fundamental,
we get to think of some ofthe most entrancing paradoxes
of our universe, and applications.
People are building quantum computers
and quantum sensing that can be useful.
I appreciated that balance.
- So, Nicole, we've beentalking to you a lot
about your book, but Iwanna make sure we also talk
(39:16):
about your research contributions.
And so I attended your colloquium here
at Perimeter yesterday,
and at one point, you had a slide
and it was called Many-BodyLocalization Auto Cycles.
And I'm not gonna ask you about that,
but at the bottom of the slide,
you had some small text that said,
"Ask me about my favorite symmetries."
(39:38):
So since you said, I have to ask:
Can you tell us about thosefavorite symmetries of yours?
- One growing subfield
that I've been dedicating a lot of time to
is a quantum generalization
of a very, very simple problem
from undergraduate statistical physics
or thermodynamics class.
(40:00):
Very often we think about asmall system exchanging stuff
with a big environment.
One of the favoriteexamples in thermodynamics
is a cup of coffee.
A cup of coffee cools,
it exchanges heats and particleswith the air around it.
We often think about this small system
as exchanging energy or particles
(40:21):
or maybe electric chargewith the environment.
These are properties that are measurable.
Quantum systems haveproperties that are measurable,
but that you might not be ableto measure simultaneously.
They participate inuncertainty relations together.
What's really interestingabout quantum theory
(40:44):
is what happens when youhave these properties
that can't be measured simultaneously,
that participate in anuncertainty relation.
Very oddly, across the decades
from the origins of thisproblem until a few years ago,
people basically didn'tthink of the question,
(41:06):
what happens to this simple setup
that I've described that isin many an undergrad textbook
if the properties thatthe small system exchanges
with the big environment arethese incompatible properties
that we can't measure simultaneously
and that participate inan uncertainty relation?
(41:26):
It's a really, really basic question
because it takes a textbook problem
and adds one quantum twist.
But some very common arguments
in thermodynamics rely onthe assumption implicitly
that we didn't realizeuntil a few years ago
that these properties aresimultaneously measurable.
(41:47):
So my group, as well as someother groups around the world,
are exploring the ratherquantum thermodynamic question
of what happens if wetake this simple setup
and enable the propertiesto be incompatible?
It turns out it's not clear
whether the small systemcan even thermalize.
so come to be at the same temperature
(42:09):
and so on as its environment.
- A lot of the researchthat you're describing here
and in the book seems very cutting edge
and theoretical sort of blackboard work,
but it's not entirely.
There are connections toexperiment and to application.
Can you tell us wherewe are in that process
between theory and experiment
and application inquantum steampunk terms?
(42:31):
- Yes.
Quantum thermodynamicshas its roots in theory
for quantum thermodynamicsdeveloped first during the 1930s.
There was some work duringthe ensuing decades.
There has really been ahuge burst of activity
over the past decade or so.
The earlier quantum thermodynamicworks were theoretical
(42:55):
and even, to some extent,philosophically minded.
That drew me into the field
and drew me in part to Perimeter.
Then I went to Caltech,
which has a lot of experimental activity.
So I was increasingly exposed
to experiment during the course of my PhD,
increasingly came to interactwith experimentalists.
(43:16):
And as a postdoc, I ended up starting
to collaborate a whole lot
with lots of differentexperimental groups.
That's also kind of the story
of how quantumthermodynamics has progressed
from theory to experiment.
The past decade has seen the ability
to perform quantumexperiments that the founders
(43:37):
of quantum theory thoughtwould be impossible.
Experimentalists have amazing control
over atoms, ions, photons,
artificial atoms, and more.
Quantum thermodynamicistshave increasingly
been taking advantage of
that wonderful control achieved in labs.
Labs have been realizing quantum engines
(44:00):
that have been proposedsince the late 1950s.
They've been realizing refrigerators
and quantum batteries and so on.
- And some of your ownresearch is currently being put
to the experimental test.
Is that right?
- Yes, I am currentlyworking with four labs.
One uses photons, one uses ions,
(44:20):
and two use artificial atoms.
- And what is the thegoal of that research
or the focus of it?
- Different projectshave different focuses.
For instance, an experimentthat was recently completed was
in this subfield of quantum thermodynamics
that I just discussed,
that involves the exchangeof thermodynamic properties
(44:44):
that can be quantum incompatible.
It was not clear for a while
that this little system analogous
to the coffee cup could thermalize,
come to a quiet state,
in which there's no net flow of anything,
such as energy or particles in and out,
and it has the same temperature
and some other propertiesas its environment.
(45:07):
We've increasingly gainedevidence that this small system,
even in this particularly quantum setup,
at least approaches thermalization,
although we don't know exactlyto what extent it does.
Together, with some theorist colleagues,
proposed an experiment forobserving whatever degree
of thermalization we could.
(45:29):
Christian Roos' group
in Innsbruck, Austriaused a set of trapped ions
as their whole system,
the small system and the environment.
A couple of the ions formedthe little system analogous
to the cup of coffee,
and the rest of the ions
in a chain of ions formedthe environment analogous
(45:51):
to the air with which thecoffee cup exchanges heats
and particles.
So they set up theseions in a certain way.
They let the ions evolve
and exchange different properties.
Then they measured the two ions
and found that they did
at least approach thermal equilibrium.
(46:13):
- You mentioned quantum refrigerator.
Can you explain what that is?
Again, it's not a very small refrigerator.
It's something else entirely,
but we have this picture in our heads
of what a refrigeratoris and what it's for.
Is that picture at all related
to the quantum analogous refrigerator?
- I think of a refrigerator as anything
that uses a resourceto cool down a system.
(46:36):
I'm working with Simone Gasparinetti's lab
in Sweden at Chalmers University
on building a quantum refrigerator.
It consists of superconducting qubits.
Superconductors are quantum systems.
They're little circuitsin which current can flow
for all time without ever dissipating.
(46:58):
Superconducting qubits are being used
as the physical systems
that encode basic unitsof quantum information
in many quantum computers.
Chalmers University isbuilding a quantum computer.
A superconducting qubitquantum computer needs
to be at low temperatures.
If the quantum computerhas just run a calculation,
(47:19):
then it's effectivelyfilled up its scrap paper.
These superconductingqubits act like scrap paper
that has been scribbled on.
They need to be reset.
They need to be, in a sense,
erased like scrap paperfor the next calculation.
They are reset if theyare cooled down even more.
This quantum refrigerator will be inside
(47:42):
of the preexisting classical refrigerator
that keeps all of thesuperconducting qubits
at a low temperature.
And the quantum refrigerator has the job
of cooling down theseused qubits even more.
The experiment is supposedto be happening right now.
We have numerical simulations.
(48:02):
We'll see how well those are born out.
- I've heard you talk about the fact
that the initial idea for oneof your research projects,
which I know has now been published
with a team of your collaborators,
first came up over an informaldiscussion over coffee.
And I think this type
of thing actually happens pretty often,
(48:23):
maybe more often than we might think.
It actually happened tome as well during my PhD
that a project that I endedup spending a lot of time
on came up over a discussion at lunch.
Although, I wasn't partof that discussion,
but I ended up working on the project
that resulted from that discussion.
I'm just wondering if you cantalk a little bit about that
(48:43):
and maybe what you think is so special
about those spontaneous discussions
that between researchers.
- This collaboration began during my PhD
when I was at Caltech.
There is a condensed matter theorist,
Gil Refael, at Caltech.
He has an office in abuilding called Bridge.
(49:04):
But most often I saw himat the Red Door cafe.
After lunch one day, Iwas at the Red Door Cafe,
he was at the Red Door Cafe, and he said,
"Hey, you're interested
in breaking the second lawof thermodynamics, right?"
Personally, I think that thesecond law of thermodynamics
probably cannot be broken,
but I am extremely enthusiastic
(49:26):
about the second law of thermodynamics.
So I asked, "What are youinterested in discussing?"
And he said, "There'sthis phase of matter,
many-body localization."
This phase was very, very popular.
It was undergoing a lot ofstudy when I was in my PhD.
Gil contributed a lot to that research.
He said, "We've been studyingmany-body localization
(49:48):
for a while now.
And it's interesting froma physics perspective,
but what is it good for?"
So many-body localizationis a phase of matter
of quantum many-particle systems.
The behavior of a many-bodylocalized system contrasts
with ordinary behaviorthat we might expect.
(50:09):
Let's go back to the example
of a classical gas in a box.
Suppose that we have aclassical gas in a box,
we measure its particles' positions,
and we find that the particlesare all clumped together
in one corner of the box.
Shortly thereafter,
the particles willspread all over the box.
(50:29):
They won't hang aroundin the same positions.
However, if we have amany-body localized system,
which could consist ofa bunch of cold atoms,
and we measure the positionsof these particles,
then those particles willapproximately hang around
in the positions fora long time afterward,
(50:51):
in contrast with the behaviorthat we would expect.
A many-body localizedsystem has some resistance
to the second law of thermodynamicsand the flow of time.
If we're thinking aboutthe classical gas in a box,
we know time is flowingif we're watching the gas
because we see the gasexpanding all across the box.
That's why we think ofmany-body localization as,
(51:12):
in some sense, resisting thesecond law of thermodynamics
a little bit, although, eventually,
the particles do spread out.
Many-body localization had been proposed
as a possible quantum memory
for storing quantum information
since things tend to stay put in it.
But Gil was thinking,
just as there areinformation processing tasks,
(51:34):
such as storing information,
there are also thermodynamic tasks.
So maybe I should ask aquantum thermodynamicist
what we can do with this resource.
We talked for a while,and we eventually brought
into the project two more collaborators:
Christopher White andSarang Gopalakrishnan.
We came up with theidea of a quantum engine
(51:57):
that can be changed
between this many-body localized phase
and a more thermalizing phase of matter
in which particles andinformation spread out quickly.
Many-body localization is a long name
that has very many letters and syllables,
so it's often called MBL.
(52:18):
Gil came up with a wonderfulname for the engine,
the MBL mobile.
- We've been asking youa lot about your book
and now about your research,
but I also wanna ask youabout something kind of
at the intersection of those two.
Can you tell us if writingthe book helped you at all
with your research?
- Absolutely. It was extremely helpful.
On the one hand, I had toextract the basic physics
(52:41):
from a lot of differentthermodynamic discoveries.
When I think of a highlycompetent theoretical physicist
whom I admire, I think of someone
who can explain a discovery
in terms of just the basic physical story.
That person knows what's really essential,
(53:01):
what's really important,
so they don't bog down the explanation
with a lot of unnecessary details.
I had to extract the basic physics
from discoveries in this way,
and that helped me understanda lot better what was really
behind these thermodynamicsettings and findings.
(53:23):
Also, I had to write at the end
of my book what I thoughtwas ahead for the field.
I started thinking fromquantum thermodynamics,
we've gained wonderfulfundamental insights.
Can quantum thermodynamicsalso be practical?
What would it take forquantum thermodynamics
to be practical?
The original theory ofthermodynamics went hand in hand
(53:43):
with the Industrial Revolution,
which was extremely practical.
It would be wonderful
for the quantum thermodynamic engines
and refrigerators and so on
that have been proposedto lead to utility.
I mentioned that experimentalists
have realized quantumthermodynamic engines.
(54:05):
These experiments are proof of principle.
They show that if we work really hard,
we can create and run quantum engines,
but we tend to have to invest more work
in cooling the engine downand in manipulating it
than we can extract using the engine,
which is quantum, so it'sjust a little bit of energy.
(54:27):
I thought about what we would really need
to make quantum thermodynamics practical.
I started thinking about solar panels
in Southern California.
My PhD advisor, John Preskill,
has solar panels on hishouse in Southern California.
He can use solar panels to great effect
because he happens to be in an environment
(54:48):
where they fit in and just dotheir own job very usefully.
If we were in Buffalo instead,
solar panels would not be so helpful.
I think of the quantum engines
that have been realized today
as kind of similar tosolar panels in Buffalo.
We have to spend a lot of work on them,
just as you would have to spend a lot
(55:08):
of work scooping snow offyour solar panels in Buffalo.
I started looking around
for a quantum thermodynamic context
for quantum thermodynamic technologies
that is, frankly, like SouthernCalifornia for solar panels.
Shortly after writingthat section of my book,
I got an email from Simone Gasparinetti,
(55:30):
the experimentalist that I mentioned
who I'm working with in Sweden.
I was not working with himat the time, but he said,
"I'm starting up a lab.
How about we chat
about what you thinkare great opportunities
for quantum thermodynamic experiments?"
And I said, "Recently, I've been thinking
about this need for aquantum thermodynamic setting
that's like SouthernCalifornia for solar panels.
(55:51):
I want to make quantumthermodynamics useful."
I should also mention I'm not
the only quantumthermodynamicist who would like
to make quantumthermodynamic devices useful.
There are other peoplearound the world thinking
in this direction, butI'm just telling the story
of how I came to this direction
and this collaborationand this experiment.
And Simone said, "Ah,I have such a setting."
(56:12):
And so we embarked on this adventure
of developing a quantumthermodynamic refrigerator
that we wouldn't have to spend a lot
of control on in operating,
that would just do its own thing
to reset qubits aftera quantum computation
in a superconducting qubitquantum refrigerator.
(56:33):
So the book has absolutely been useful
for my physics research.
- To follow up on that,
are there any sort ofbig-picture breakthroughs
or advances in your field?
That, you know, you're stillquite a young researcher
with a long runway ahead in research.
Are there breakthroughsthat you hope you'll see
or even make in your career?
(56:54):
- I am very fascinatedby this growing subfield
that I mentioned before
that involves incompatible properties
of quantum thermodynamic systems.
There are a lot of reallyfundamental questions
that haven't been thought about.
For instance, to what extent does
the small system reachthermal equilibrium?
(57:15):
Also, I think there arereally interesting discoveries
to be made when we take this idea
and bring into other fields.
For instance, the last timeI was in Santa Barbara,
I went to a many-body physicist.
There is toolkits inmany-body physics called,
it also has a horrendously long name,
(57:36):
the eigenstate thermalization hypothesis.
It helps us understand whyquantum systems thermalize.
Why, in some sense, time flows
for them in some ways similarlytoo for classical systems.
This many-body physicist in Santa Barbara,
Mark Srednicki, callshimself the high priest
of the eigenstatethermalization hypothesis.
(57:59):
He was one of the people
who helped create this toolkit.
It's very powerful.
It has been transformativefor quantum many-body physics.
It's been used an enormous amount
over the past few decades.
And I asked, "What if we try to apply it
to a system that has theseincompatible properties
that are being exchanged?"
And he said, "You know, Ihadn't thought about that."
(58:21):
And it turns out that thistoolkit needs to be changed.
This toolkit that has beenaround for many decades.
I think that there are othersuch realizations waiting
to be had in this subfield.
- You've been so generous with your time,
and you have a conference to get back to.
Thank you so much forsitting down to chat with us.
It's just been a pleasure.- Thank you again
for having me on the podcast.
(58:41):
It's really been a pleasure.
(upbeat music)
- Thanks so much for listening.
Perimeter Institute is
a not-for-profit charitable organization
that shares cutting edgeideas with the world thanks
to the ongoing support
of the governments of Ontario and Canada,
and also thanks to donors like you.
Thank you for being part of the equation.
(59:02):
(upbeat music)
(upbeat music)
- Hello, everyone, and welcome back
to Conversations at the Perimeter.
On this episode, Lauren and I chat
with Nicole Yunger Halpern.
She is a quantum thermodynamicist,
which is just about ascomplicated as it sounds,
(00:21):
but thankfully Nicole isgifted at explaining it,
and she's done so in thecontext of steampunk,
the science fiction genre
that is sort of set inthe Industrial Revolution.
And she's the author ofthe book by that title,
"Quantum Steampunk (00:34):
The Physics of Yesterday's Tomorrow."
- I always really lovetalking to physicists
who work at the intersectionof different fields,
so it was really fun to talk to Nicole
and get to hear about her work
at the intersection of quantum physics,
information science, and thermodynamics.
Nicole joined us for this recording
when she was visiting PerimeterInstitute for a conference,
(00:56):
but she also shared abouther times at Perimeter back
when she was a student within
the Perimeter ScholarsInternational master's program,
which I also work in as ateaching faculty member.
- So without further ado,
let's dive into the worldof "Quantum Steampunk"
with Nicole Yunger Halpern.
(upbeat music)
Nicole, thank you so much for being here,
(01:16):
and welcome back to Perimeter Institute.
- Thank you. It's reallya pleasure to be here.
Thanks for having me on the podcast.
- I've just finished reading your book,
The Physics of Yesterday's Tomorrow,"
and we're so keen to talk to you about it
because the ideas of quantum
and steampunk I've never heardcombined this way before.
And I honestly have never read a book
(01:38):
about thermodynamics before,
certainly not quantum thermodynamics.
So I'm hoping you can take our audience
on a little bit of a backward journey.
And what's meant by theterm "thermodynamics,"
and is it as scary as Ialways thought it was?
- I would say it's not as scary.
The thermodynamics issimply the study of energy,
the different forms that energy can be in
(01:59):
and the possible transformationsamongst those forms.
The theory of thermodynamicswas developed during the 1800s.
It was inspired by theIndustrial Revolution.
For the first time,
steam engines were being usedon a large scale in industry,
and people wanted to figure out
how efficiently they could operate.
So they gave thermodynamicsthis practical bent,
(02:19):
thinking about powering factories
and cooling systems down,
and nowadays, also charging batteries.
So thermodynamics hasthis practical viewpoint,
but it's also become very foundational.
This is a side of it that I really love.
In thermodynamics, we end up thinking
about questions like why time flows
(02:41):
in only one direction.
And the thermodynamicistsof the late 1800s also got
to wrestle with fundamentalquestions about atomism.
So the theory of atoms hadn'tbeen entirely well accepted
by the Victorian era.
So people were debating about
to what extent its useful
or scientific to talk about tiny particles
(03:02):
that no one can even see.
Thermodynamics appeals to me in part
because of this fundamentalspirit that it has.
And as you mentioned,
I also see its modern incarnation,quantum thermodynamics,
as sharing its aesthetic with steampunk.
Steampunk is a genre ofliterature, art, and film.
(03:24):
Steampunk stories take placeduring the Victorian era.
There are settings such as greedy,
nighttime, dangerous London Streets,
Sherlock Holmes in London, Meiji Japan,
and the Wild wild West.
In these settings arefuturistic technologies,
such as time machines, thedirigibles, and at automata.
(03:49):
There's this beautifulblend of old and new
that creates both a sense of nostalgia
and a sense of adventureand exploration and romance.
In my field, which is at the intersection
of quantum information and thermodynamics,
we're taking the theory ofthermodynamics from the 1800s,
(04:10):
which was built forlarge, classical systems,
such as steam engines.- Like steam engines.
That is quite right.- Exactly.
- I always think of theIndustrial Revolution
and thermodynamics, Ithink of steam trains.
- Exactly.
Nowadays, experimentalistshave great control
over quantum systems,
and the cutting edge technology of the day
is not so much the steam engine,
but cutting edge technologiesinclude quantum devices,
(04:33):
such as quantum computersand quantum sensors.
But we need to take thistheory of thermodynamics
from the 1800s and extend it
and really re-envisionit for the 21st century.
In the first place,
how do the thermodynamic laws still hold
for quantum systems?
How can we reformulatethem for quantum systems
(04:53):
and how they encode and interplay
between energy and information,
especially quantum information?
Also, we know from thequantum information revolution
that quantum phenomena,such as entanglements,
can enhance information processing tasks,
such as certain computations.
Just as there areinformation processing tasks,
(05:14):
there are thermodynamic tasks,
such as charging batteriesand powering cars.
So given that quantum phenomena
can enhance information processing tasks,
can they enhance thermodynamic tasks?
In this intersectionof quantum information
and thermodynamics, wehave, on the one hand,
the thermodynamic theoryof the Victorian era,
and on the other hand,
(05:36):
the futuristic technologiesof quantum computing
and the cutting edge scienceof quantum information theory.
I see this fusion of old and new
as sharing its aesthetic with steampunk.
- When I think of quantum thermodynamics,
the very first simple image
that popped into my head was avery, very small steam train.
And I know that's not right.
(05:56):
Can you tell us what's meant more broadly
by the term "quantum?"
What does quantum describe,
and how does it connect to thermodynamics?
- I think of quantum physics
as very loosely beingthe physics of the small.
What we mean by smallcan depend on context.
If you have a lot of particles
that are crammed into space small enough
that they interact very strongly,
(06:17):
then that space might beas large as New York City.
In which case, the particles
that are crammed very closelytogether form a black hole.
Quantum physics isrelevant to black holes,
even though black holes seem large
in the sense that NewYork City seems large.
But the particles arecrammed so close together
that they interact very strongly,
so we can't describe them
(06:38):
with just the physicsfrom before the 1920s.
That's how I think of quantum.
You also mentioned the possibilityof quantum steam trains.
Quantum engines have been developed.
They've been designed by theorists
and now realized experimentally.
It turns out that quantum engine can be
as small as a single atom.
(06:58):
That was the basis forthe first quantum engine
that was proposed in 1959,
and then in more detail in 1967.
- So I have to tell you, Nicole,
I actually have some cousinswho listen to this show,
and they work as mechanics for aircraft
and specialized vehicles.
And I was particularlyexcited to talk to you today
because I think that you could allow me
(07:20):
to learn a bit more aboutsomething that they do.
So can you actually tell usreally what an engine is?
- We could focus on a heat engine
since that's a simpleand canonical example.
And in particular, a heatengine that's some device
that has access to twodifferent environments
at two different temperatures.
(07:41):
Heat naturally flows fromhot systems to cold systems.
And an engine is a device
that takes some of thisheat that is flowing
and turns it into work.
Heats and work are the two different types
of energy that can betransmitted between objects.
Heat is random energy. It's uncoordinated.
(08:01):
It's the energy of particlesjiggling all about.
Work is organized, coordinated energy
that can be directly harnessed
to do something usefullike push a rock up a hill.
So a heat engine uses thisdifference between temperatures
and takes the random heats
and transforms it into useful work
(08:23):
while not changing itself very much.
- And what is the quantum version of that,
the relationship between heat and work?
- What is quantum heat
and what is quantum workare some of the fundamental
and trickiest questionsof quantum thermodynamics.
(08:43):
I gave some intuition about what heats
and work are in classical thermodynamics.
We can take those intuitions
and try to apply them to quantum systems,
but here's a simpleexample of why defining
or conceiving of quantumheat and work is tricky.
Suppose that we want to measure
(09:03):
how much heat a system absorbs.
We can measure its energy,
then let the system absorb the heats,
and then measure the energy again.
The amount of energy it has
at the end minus the amount of energy
that it has at the beginningis the heat absorbed.
But suppose that we try thisprocess on a quantum system.
(09:24):
If we measure a quantumsystem, we disturb it.
And if we measure aquantum system's energy,
we actually change its energy.
So by trying to measure the heat
or work absorbed by a quantum system,
we can change the amount of heat
or work absorbed by the system.
- And that doesn't happenin the classical sense.
That's only when you'redealing with quantum particles.
- Right.
So we have to think about quantum work
(09:46):
and heat totally differently.
There's a whole spread
of different definitions of quantum heat
and quantum work thatdifferent people have proposed.
I think of it as a menagerie.
So every time I find a new paper
with a new definition ofquantum heat and work,
I add it to this filethat I call menagerie
of quantum heat and work.
(10:06):
I think of the definitions
as different species in the menagerie.
I think that differentdefinitions of quantum heat
and work are useful in different contexts.
There is a very well-known trend
in theoretical physics to unify,
to put different definitions
and theories and ideas together
to make some one unified theory,
(10:28):
especially at the Perimeter Institute.
However, I think that
in this very operationaltheory of thermodynamics,
where we're really thinking about agents
who are given some resources,
like environments atdifferent temperatures,
they're trying to perform taskslike a refrigerator system,
it can be useful to define heat
and work in terms of whatsort of a system we have
(10:51):
and, in particular, what we can do to it.
How we can perform work on it,
how we can poke it, how we can measure it.
What systems we havearound, like batteries,
that they can interact with.
- I love that in your bookyou provide some really sort
of straightforward examples,
including beautiful illustrations,
which I want to talk about too.
But the examples, a lot of theminvolve a particle in a box.
(11:13):
And it's so simple.
I'd never thought of thermodynamics
as being something that you could explain
with particles in boxes.
Can you tell us why that's such a sort
of standard explanation thatyou go back to frequently?
- We very often think
in thermodynamics about gas in a box.
It's quite possible thatmany listeners learned
(11:35):
in chemistry class in high school
about ideal gases, their idealizations.
They have very simple properties,
though they're described
by pretty simple equations, in many cases,
but they exhibit reallyinteresting phenomena,
such as they provide great examples
of the second law of thermodynamics,
(11:55):
which explains or helps usunderstand why time flows.
They have properties like volume
and pressure that are measurable.
And by thinking about howthe particles are acting on,
say, the walls of their boxes,
beating against the boxes' walls.
We can think of what pressure even means.
This is a great playground
for understanding thermodynamicquantities like pressure
(12:16):
and volume and entropy.
Also, in quantum theorywe like thinking a lot
about particles in boxes.
Very often we think aboutsingle particles in boxes.
So in the book, there are some examples
of really, really evenmore idealized simple gases
that consist even of single particles.
- And can you take usback to how you combined
(12:38):
or blended these ideas of thermodynamics
and quantum mechanics and steampunk?
Like, where did that come from?
How did you make those connections?
- That's a good question.
I encountered some steampunkworks as I was growing up.
For instance, I loved the book series
the "Chronicles of Chrestomanci"by Diana Wynne Jones.
(12:59):
She was a wonderful andaward-winning fiction writer,
one of the best sciencefiction fantasy writers
of the 20th century, notjust according to me,
but also authors thatlisteners might know,
like Neil Gaiman.
I encountered her worksand Philip Pullman's works.
I didn't realize, though,that steampunk was a genre.
I didn't quite recognize whatit was that I was reading.
(13:22):
I didn't recognize thatthere was some unifying idea
across these works.
Then, at the beginning of grad school,
somehow I discovered thatsteampunk was a genre.
By then, I had come to this intersection
of quantum information and thermodynamics,
and I suddenly just realizedthat it has the aesthetic
and the spirit of steampunk.
(13:43):
I was so delighted to findthis shared connection
between the hardcorephysics that I was doing
and the genre ofliterature, art, and film.
I wrote a blog post about it right
at the beginning of my PhD.
I blogged for Caltech's Quantum Institute.
Then the idea started developing.
It ended up the title of my PhD thesis,
(14:05):
and then the name of myresearch group in Maryland,
and then I wrote a book.
- You mentioned grad school.
That was here at Perimeter, right?
- I earned my master's
at the Perimeter ScholarsInternational Program.
Then I was at Caltech for my PhD.
- And I remember reading, I believe,
in the book that it was atthe Waterloo Public Library,
which is just across the street,
(14:26):
that you came across a bookthat had steampunk elements.
Can you tell us what you found
in that book that inspired you?
- During most of my year in PSI,
Perimeter Scholars International,
I was in the Perimeter library working
something like 12 hours a day.
So I didn't have time to go tothe Waterloo Public Library.
(14:46):
But in the spring, classes ended,
and so I finally had a few free hours.
And I explored theWaterloo Public Library.
I found a novel by the Canadianpoet Jay Ruzesky called
"The Wolsenburg Clock."
It is about an old, old clock in Austria.
The author constructs this story showing
(15:07):
how the clock is affected by
and affects different people
in this town throughout the centuries.
One of the scenes takesplace during the 1800s.
An inventor is about to clean up the clock
and redesign it
and really invest it withthe spirit of what he does,
(15:30):
which is build automata.
So there's a scene in which he is standing
on a balcony gazing down at a ballroom
that he's converted into his workshop.
His children and wife
and so on are buildingclockwork-driven elephants
and snakes and snake charmers.
And he has this coat onthat billows out behind him.
(15:51):
- He sounds very steampunk.
- Exactly. That scene stuck in my mind.
And shortly thereafter,
I realized that that scene was steampunk.
And shortly after that,
I realized that my research was too.
- So did you always know
from the time you started your PhD
that that's what you wantedto focus your thesis on?
- Yes.
During the end of my undergrad years,
(16:14):
I increasingly found my way
to quantum information theory,
and I asked professorsin my physics department
who does the kind ofquantum information theory
that I'm interested in.
It was an abstract mathematical flavor.
They pointed me to some webpages
(16:34):
of some faculty members across the world.
I increasingly honed in on phrases
and ideas that really spoke to me.
I found that they wereat this intersection
of quantum informationtheory and thermodynamics,
where people are thinkingabout uncertainty
and entropies and information
and energy in a fundamental way.
(16:55):
Shortly thereafter, I came to Perimeter.
I had the wonderful good fortune
to work for my final project
with someone who was apostdoc here at the time,
Markus Muller, and Robert Spekkens,
who's a faculty member here.
We worked on a topicin quantum information,
theoretic thermodynamics.
(17:15):
At the end of the project,we said to each other,
"Okay, so now we've gained this toolkit.
What shall we do with it?"
I came up with a project,
and that was the first project in my PhD.
There was always another project
and more collaborators to reach out to.
- Since we're asking youabout your PhD right now,
as part of this show,
we collect questions fromsome of our listeners.
(17:37):
And a current PSI studenthere named Anna Knorr sent
in a question about your thesis.
- In your thesis, youwrite, "Steampunks dream it,
Quantum informationthermodynamicists live it."
Is that simply a cool slogan,
or does it truly motivate you
and drive you in your research?
(18:00):
- Steampunk is a genre ofscience fiction and fantasy.
It is seen as something that isn't true.
However, I do believe that it is coming
to life in the intersection
of quantum informationtheory and thermodynamics.
Thermodynamics wasdeveloped during the 1800s.
(18:21):
We carry a bit of theVictorian era with us
when we're doing thermodynamics.
And quantum computers arefuturistic technologies.
We're still building them.
And quantum information theoryis cutting edge science.
So I do believe that quantuminformation thermodynamicists
really are living what
until now has been seenas a fiction, steampunk.
(18:44):
- And in a lot of whatyou've been talking about,
you've been saying your work is really
at an intersection of several fields,
one of which is information science.
And I'm wondering if you can talk
a little bit more about information.
I know in your book you say
that we live in an information age.
So can you tell us a littlebit about why you said that
and maybe first just what information is?
(19:06):
- I've heard twodefinitions of information.
One that's a bit easier to explain
is information is the ability
to distinguish between alternatives
or a necessary ingredient
for distinguishing between alternatives.
For instance, when youget up in the morning
and need to figure out what to wear,
you need to know what the weather is like.
(19:27):
So you peer through the window, perhaps,
and see that there's sun or there's rain.
When you've peered through the window,
you've gained information.
You've been surprised.
So information is thatwhich gives us the ability
to distinguish whetherit's sunny or rainy.
- And is information itself thermodynamic?
(19:48):
Does information have anenergy component to it,
or does quantum informationhave an energy component to it?
- Information plays arole in thermodynamics.
For instance, in my book,
I walk through some examples that show
that we can use informationto turn heats into work.
(20:10):
We said that heat is random,uncoordinated energy,
and work is coordinatedenergy that's directly useful.
If we have information,
then we can run what's sometimes called
an information engine totake those random heats
and convert it into useful work.
We can also run the enginebackwards and perform work,
(20:34):
such as by draining abattery, to gain information.
There's certainly an interplay
between information and energy.
- And Nicole, when I first got your book,
the first thing I did was,of course, to flip through it
and admire the reallybeautiful illustrations
that Colin already talked about,
but when I did that,
there was one phrase that jumped out
(20:54):
to me right from the beginning.
And it's on page 19where you have a section
that's called The Liverof Information Theory.
Can you tell us a little bit about this?
- Yes.
When I was in high school,
I had a biology teacher who said,
"If you ever don't know the answer
(21:15):
to a question on a test of mine,
you should write down 'liver.'"
(Colin laughs)
The liver turns out toperform a ridiculous number
of functions in the human body.
So if you don't know theanswer to a biology question
and you answer liver,
then you have ananomalously high probability
of being correct.
Similarly, in informationtheory, if you're asked,
(21:38):
"What is the optimal efficiency
with which we can perform someinformation processing task?"
and you answer, "It'sgiven by an entropy,"
then you have an anomalouslyhigh probability being correct.
So very often in informationtheory the answer
to a question is entropy.
So I think of entropy as theliver of information theory.
(21:58):
I should also mention,
partially in response toColin's recent question,
that entropy is a manifestation
of information in thermodynamics.
Entropy is a measure of uncertainty,
how little we know.
And entropy comes up even
in the second law of thermodynamics,
(22:20):
which is a very, veryfundamental statement.
- Yeah, entropy is aconcept you hear a lot
in different branchesof physics and science.
And honestly, it's one
that I have troublewrapping my head around.
I hope I'm not alone in that.
Can you give us a bit more of an idea?
What does that mean to say
that entropy sort of playsa role in information?
- First, there are manydifferent entropies,
(22:42):
and entropy is a measure of uncertainty.
At least that's how I think of it.
For instance, I recentlylived in the Boston area,
and I came to learn that the weather
in the Boston area is avery, very random variable.
On any given day, there's some probability
that the weather will be mostly sunny,
some probability thatit'll be mostly rainy,
(23:02):
some probability thatit'll be mostly cloudy,
some probability thatit'll be mostly snowing.
If on any given day youlearn what the weather is,
then you gain some amount of information,
you are surprised by some amount,
and a measure of how surprised you are
is an entropic quantity.
It depends on how probablethat weather pattern was.
(23:24):
Also, suppose that youperform this process
on many, many days.
On each of many, many days,you learn what the weather is,
and you average youruncertainty over many days.
This is another measure of uncertainty.
There are differentmeasures of uncertainty
that describe different contexts.
So there are different entropies.
I've described entropy in aninformation theoretic way.
(23:48):
We can also see how it shows up
in thermodynamics viayour favorite example
of a gas in a box.
- Mm-hmm.
- Suppose that there is some gas in a box.
It has some large-scale properties
that characterize the gas as a whole,
such as the energy of thegas, the volume of the gas,
the number of particles in the gas.
(24:09):
But we might have just this little bit of,
or, I shouldn't say bits sincethat's a technical term here
in information theory context.
Suppose that we just know thesefew large-scale properties.
We could also zoom in on the gas particles
and realize that, at any given instant,
the gas particles have some positions,
They have some momenta.
(24:29):
So they have some masses,
and they're moving with certain speeds
in certain directions.
There are many of thesemicroscopic configurations
that are consistent withone large-scale picture
of energy and volume and particle number.
If we know just thoselarge-scale properties,
then how ignorant are we
(24:51):
of the microscopic configuration?
That's a thermodynamic entropy.
- Lauren's last question reminded me
that one of my favoriteparts about your book
is the chapter titles and the subtitles.
They're are some of the mostcreative ones I've ever seen,
including How to Insult aQuantum Information Theorist.
so I'm hoping you can tell us,
how do we insult a quantuminformation theorist?
(25:13):
- Say, "Oh, quantum information theory.
Isn't that all just linear algebra?"
- So if I were a quantuminformation theorist,
why would I be insulted by that?
- I can explain with a story.
When I was an undergrad,
I took a linear algebra course,
and I was asked toexplain what I was doing.
I said, "I'm learning
(25:34):
to solve basically thesimplest equations."
These are actually the kinds of equations
that we encounter in middle school.
And in response I was told,
"And for this you had to go to college?"
(Colin laughs)
So linear algebra is a somewhatstraightforward extension
of what we learn in middle school.
Except in middle school,
we don't deal with tens
or hundreds of these equations at a time.
(25:56):
- And on the topic oftitles and subtitles,
I don't wanna risk givingaway too many spoilers
because I want people to read your book,
but the subtitle of your entire book
is The Physics of Yesterday's Tomorrow,
and this is also the titleof a chapter in your book.
Can you tell us a littlebit about this title?
- I wish I could take credit for it,
(26:17):
but my acquisitions editor
at Johns Hopkins University Press,
together with her team,
came up with this subtitle.
And as soon as I saw it,I fell in love with it.
I think of this subtitle
as embodying the ideaof quantum steampunk.
It is a branch of physics,as well as chemistry,
but it is the physicsof yesterday's tomorrow
(26:40):
in that quantum steampunk re-envisions
the Victorian era's thermodynamicsfor the 21st century.
- Because steampunk issuch a visual aesthetic,
you had an illustrator
to create these beautifuldiagrams in the book.
Can you tell us how thatcame to be and how...
I assume there's not
that many illustrators out there
(27:01):
who just know quantum thermodynamics
like the back of their hand.
How did that relationship come to be?
- The illustrator is Todd Cahill.
He's a steampunk artist,
and he actually had no experience
with quantum physics whatsoever.
So we had a lot of conversations.
I encountered him throughanother steampunk artist.
(27:22):
Couple of years ago,
the steampunk artist BruceRosenbaum reached out to me.
He had watched a talk that I had given.
I actually suspect that itwas the first colloquium
that I gave for the IQC,
the Institute for QuantumComputing, near Perimeter.
He said, "I love the spirit of this talk.
Would you like to collaborate
(27:43):
on a quantum steampunk sculpture?"
Bruce creates large, as in human size,
or even larger, interactive,
kinetic steampunk sculptures
for museums and restaurants and hotels.
I had no experience withanything like this ever before,
but it sounded likefun, so I said, "Sure."
We talked a lot about possible designs.
(28:05):
We ended up collaborating
with another artist to create a design
of a quantum engineformed from a trapped ion
with the classical counterpartof the engine on the outside.
The sculpture as a whole looks like
an armillary sphere hearkeningback to a few centuries ago.
But also, this armillarysphere is a sphere,
(28:27):
so if you show it to someonein quantum information,
they'll say, "Oh, that lookslike the Bloch sphere,"
which represents the state of a qubit,
a basic unit of quantum information.
After I started collaborating with Bruce,
I wrote this book.
And eventually, we neededto find an illustrator,
so I asked Bruce if hecould suggest anyone.
(28:48):
And he suggested Todd.
Todd was great about learningabout quantum physics
and going back and forth with me
about representing visually,in a quite beautiful way,
images that I could onlysketch in a very poor manner
'cause I have very littletraining in drawing.
- I was gonna ask if these were images
(29:08):
that you already had in your head,
or if the collaborative processwith him helped you form,
you know, how do youvisualize this stuff that is,
most of it's invisible to us?
It's at the quantum level.
- Yes.
I sketched some diagrams, but again,
I have very, very littletraining in drawing.
So I gave him my poorlittle sketches and said,
"Can you make these look steampunk?
(29:29):
Then can you add some likeflair here and there?"
And that is what he does extremely well.
So he turned my stick figure type drawings
into beautiful illustrations.
- And some of those illustrations sort
of provide explanation of what's happening
with some characters in your book.
It's a very fascinating book in the sense
(29:49):
that it's a science book kinda
with a steampunk novella woven into it,
with characters, fictional characters.
Can you tell us who those characters are
and where they came from?
- Yes.
So the book is mostly nonfiction,
but each chapter beginswith a little snippet
from a steampunk novel thatresides in my imagination.
(30:12):
There are characters in that story.
The main characters are calledAudrey, Baxter, and Caspian.
They have this nemesis, Ewart.
I enjoyed playing withthe tropes of steampunk
in what is otherwise a very serious novel
about hardcore science.
I tried out this strategywhen writing an article
(30:35):
for Scientific Americana couple of years ago.
I was asked to write an articleabout quantum steampunk,
and I thought that itwould be fun to start
with something quite different
from the hardcore sciencethat quantum steampunk is,
to start with this playfulsnippet from an imaginary novel
to illustrate what steampunk is.
So I partially wanted toillustrate what steampunk is
(30:57):
for those unfamiliar with it.
Partially, I wanted to havefun playing with these tropes,
like the very spirited,
vivacious, young girl in the Victorian era
who refuses to be pinned down
by the expectations of her society
and corsets and so on and so forth.
Also, dark, dangerous London streets.
(31:19):
It was fun to play with these ideas.
They did end up helpful later on
in the chapters toillustrate scientific ideas.
Very often in an operational theory,
like information theory, wespeak in terms of agents.
I think of an operational theory
as one that can bephrased in terms of agents
(31:41):
who have certain resources
and need to perform certain tasks,
so they try to figure outhow to perform those tasks
as efficiently as possible.
Information theory is operational.
In information theory,
we think about the tasksof compressing data,
communicating information overa noisy channel, and so on.
In thermodynamics, wethink about refrigerating
(32:03):
and charging batteries andpowering cars and so on.
Many of information theory'soperational stories are phrased
in terms of characters Alice and Bob.
They have a friend, Caspian.
Sometimes they are eavesdropped on by Eve.
So I gave the characters
in this imaginary steampunk novel names
(32:25):
that begin with the sameletters, A, B, C, and E.
- It's funny, I didn'teven put that together
until just now.
We are actually sitting
in the Alice room directlybelow the Bob room just
to demonstrate how commonlyused those terms are in science.
- Yes, very relevant.- Sorry, go on. (chuckles)
- I figured that some readers would see
that very quickly, and other readers,
say, who might come fromthe steampunk community,
(32:47):
would maybe not make the connection
between Audrey and Alice,
but instead would recognize more
of the steampunk tropesand smile at those.
I thought referring tocharacters such as Alice
and Bob is really helpfulfor explaining our science
and formalizing information theoretic
and thermodynamic tasks.
(33:08):
But we refer to Alice and Bob so much,
it would be fun to havedifferent characters.
Hence Audrey and Baxter and so on.
- I think this is justreally what makes your book
so unique, is that the steampunk
is really infused all the way throughout.
And we actually gotanother question sent in
on a related topic.
This one is from Matt Duschenes,
who's currently a PhD student
(33:29):
at the Institute for Quantum Computing
and the Perimeter Institute.
- So you found a great connection,
and we're really inspiredby the genre of steampunk
to drive your research directions.
Do you think there aremore serious opportunities
for this kind of inspiration,
and that physics as a field should look
to draw more connections with art?
- I think that
how quantum thermodynamicsshares its spirit
(33:50):
with steampunk is kind of a gift.
It makes doing the physics even more fun
because of this connection.
I think that it would be wonderful
to find more such connections
between fields of science andgenres of art and literature.
I've always enjoyed studying everything,
and I was drawn to physics in the manner
(34:11):
of a natural philosopher from,
say, the 1700s or early 1800s.
They studied, in a very rigorous sense,
aesthetics, as well as geometryand astronomy and so on.
I think that there's a lot of richness
that we can add to ourlives' interpretations
(34:33):
and understandings by engagingin interdisciplinarity.
That said, there's somethingthat's unique to physics,
and I think that to be a physicist,
one really needs to focusvery hard on the physics.
But something like steampunk
can provide extra energy and inspiration.
- Growing up, were you readingscience fiction novels,
(34:53):
or were you studying thermodynamics?
How did sort of yourformative years lead you
in this direction?
- I grew up reading justabout everything just
about all the time.
(Colin laughs)
I read while waiting to get picked up
from school in the afternoon.
I read while waiting for foodto arrive at restaurants.
(35:15):
I read on weekends. I read after school.
This reading taught me tobuild worlds in my head.
I always had characters andplots and settings in my head.
I think of my job nowas building universes
in my head for a living.
- So we've already asked youabout how you got interested
(35:37):
in the specific field ofquantum thermodynamics,
but I'm wondering if youcan also share with us
how you came to findyourself as a physicist.
- I did want to study everything,
so I resisted choosing amajor as long as possible.
- That was at Dartmouth?
- Yes, at DartmouthCollege in New Hampshire.
I had always hadphilosophical inclinations.
(35:58):
I always enjoyed engagingwith abstract ideas.
I had a philosophy teacher in high school
who was fascinated by the paradoxes
in quantum theory and relativity.
He didn't have any background in physics,
he would be the first to admit,
but he passed on to me acuriosity about these fields.
(36:21):
Meanwhile, I was absolutelyadoring my calculus class
and my physics class and so on.
I absolutely wanted tokeep studying those.
I found in the physics department a number
of faculty members who wereextremely good physicists.
I've come to appreciate that more and more
as I've become a colleague
(36:42):
and been able to look attheir works as a colleague.
They also had philosophical inclinations.
They also appreciated history.
They helped me construct a major
that was partway between the physics major
and the create your own major.
I took a bunch of physics courses,
and I took math, philosophy,
and history courses related to physics.
(37:04):
I got to call this major.
My spirit was very much in thephysics department, though.
And by the end of my undergrad experience,
I determined that it was physics
that I wanted to burrow into very deeply.
So after that, I tried outresearch as a research assistant
in Lancaster Universityin the United Kingdom.
Then I came to the Perimeter Institute.
(37:27):
And here, I had my first opportunity
to do research on the intersection
of quantum informationtheory and thermodynamics,
and I absolutely adored it.
- What did you adore about it so much?
- I love the foundational perspective.
I love the abstract ideas.
Entropy is a strange idea
and entropy-- Thank you. I thought so.
(37:49):
- And entropy is a function.
You can write down the mathematical form
of a typical entropy.
And it looks funny.
It has multiple piecesthat are kind of odd.
It has a negative sign.
It has two copies of aprobability. It has a logarithm.
There are good reasons
why this entropy hasthis mathematical form,
(38:11):
and I go through such an argument
in my book for why it makes sense,
but if you just look at it,it looks like an odd duck.
But on the other hand,
entropy lies behind thesecond law of thermodynamics,
which helps us understand why time flows.
That is so very fundamental.
This tension between thatfunny-looking function
(38:34):
and the very fundamental ideahad drawn me for a long time.
Also, as I mentioned,
I've always hadphilosophical inclinations.
I appreciated the fundamental nature
of the laws of thermodynamics
and the axioms of quantum theory.
I appreciated how quantuminformation theory sits
(38:55):
at the balance betweenthe very fundamental,
we get to think of some ofthe most entrancing paradoxes
of our universe, and applications.
People are building quantum computers
and quantum sensing that can be useful.
I appreciated that balance.
- So, Nicole, we've beentalking to you a lot
about your book, but Iwanna make sure we also talk
(39:16):
about your research contributions.
And so I attended your colloquium here
at Perimeter yesterday,
and at one point, you had a slide
and it was called Many-BodyLocalization Auto Cycles.
And I'm not gonna ask you about that,
but at the bottom of the slide,
you had some small text that said,
"Ask me about my favorite symmetries."
(39:38):
So since you said, I have to ask:
Can you tell us about thosefavorite symmetries of yours?
- One growing subfield
that I've been dedicating a lot of time to
is a quantum generalization
of a very, very simple problem
from undergraduate statistical physics
or thermodynamics class.
(40:00):
Very often we think about asmall system exchanging stuff
with a big environment.
One of the favoriteexamples in thermodynamics
is a cup of coffee.
A cup of coffee cools,
it exchanges heats and particleswith the air around it.
We often think about this small system
as exchanging energy or particles
(40:21):
or maybe electric chargewith the environment.
These are properties that are measurable.
Quantum systems haveproperties that are measurable,
but that you might not be ableto measure simultaneously.
They participate inuncertainty relations together.
What's really interestingabout quantum theory
(40:44):
is what happens when youhave these properties
that can't be measured simultaneously,
that participate in anuncertainty relation.
Very oddly, across the decades
from the origins of thisproblem until a few years ago,
people basically didn'tthink of the question,
(41:06):
what happens to this simple setup
that I've described that isin many an undergrad textbook
if the properties thatthe small system exchanges
with the big environment arethese incompatible properties
that we can't measure simultaneously
and that participate inan uncertainty relation?
(41:26):
It's a really, really basic question
because it takes a textbook problem
and adds one quantum twist.
But some very common arguments
in thermodynamics rely onthe assumption implicitly
that we didn't realizeuntil a few years ago
that these properties aresimultaneously measurable.
(41:47):
So my group, as well as someother groups around the world,
are exploring the ratherquantum thermodynamic question
of what happens if wetake this simple setup
and enable the propertiesto be incompatible?
It turns out it's not clear
whether the small systemcan even thermalize.
so come to be at the same temperature
(42:09):
and so on as its environment.
- A lot of the researchthat you're describing here
and in the book seems very cutting edge
and theoretical sort of blackboard work,
but it's not entirely.
There are connections toexperiment and to application.
Can you tell us wherewe are in that process
between theory and experiment
and application inquantum steampunk terms?
(42:31):
- Yes.
Quantum thermodynamicshas its roots in theory
for quantum thermodynamicsdeveloped first during the 1930s.
There was some work duringthe ensuing decades.
There has really been ahuge burst of activity
over the past decade or so.
The earlier quantum thermodynamicworks were theoretical
(42:55):
and even, to some extent,philosophically minded.
That drew me into the field
and drew me in part to Perimeter.
Then I went to Caltech,
which has a lot of experimental activity.
So I was increasingly exposed
to experiment during the course of my PhD,
increasingly came to interactwith experimentalists.
(43:16):
And as a postdoc, I ended up starting
to collaborate a whole lot
with lots of differentexperimental groups.
That's also kind of the story
of how quantumthermodynamics has progressed
from theory to experiment.
The past decade has seen the ability
to perform quantumexperiments that the founders
(43:37):
of quantum theory thoughtwould be impossible.
Experimentalists have amazing control
over atoms, ions, photons,
artificial atoms, and more.
Quantum thermodynamicistshave increasingly
been taking advantage of
that wonderful control achieved in labs.
Labs have been realizing quantum engines
(44:00):
that have been proposedsince the late 1950s.
They've been realizing refrigerators
and quantum batteries and so on.
- And some of your ownresearch is currently being put
to the experimental test.
Is that right?
- Yes, I am currentlyworking with four labs.
One uses photons, one uses ions,
(44:20):
and two use artificial atoms.
- And what is the thegoal of that research
or the focus of it?
- Different projectshave different focuses.
For instance, an experimentthat was recently completed was
in this subfield of quantum thermodynamics
that I just discussed,
that involves the exchangeof thermodynamic properties
(44:44):
that can be quantum incompatible.
It was not clear for a while
that this little system analogous
to the coffee cup could thermalize,
come to a quiet state,
in which there's no net flow of anything,
such as energy or particles in and out,
and it has the same temperature
and some other propertiesas its environment.
(45:07):
We've increasingly gainedevidence that this small system,
even in this particularly quantum setup,
at least approaches thermalization,
although we don't know exactlyto what extent it does.
Together, with some theorist colleagues,
proposed an experiment forobserving whatever degree
of thermalization we could.
(45:29):
Christian Roos' group
in Innsbruck, Austriaused a set of trapped ions
as their whole system,
the small system and the environment.
A couple of the ions formedthe little system analogous
to the cup of coffee,
and the rest of the ions
in a chain of ions formedthe environment analogous
(45:51):
to the air with which thecoffee cup exchanges heats
and particles.
So they set up theseions in a certain way.
They let the ions evolve
and exchange different properties.
Then they measured the two ions
and found that they did
at least approach thermal equilibrium.
(46:13):
- You mentioned quantum refrigerator.
Can you explain what that is?
Again, it's not a very small refrigerator.
It's something else entirely,
but we have this picture in our heads
of what a refrigeratoris and what it's for.
Is that picture at all related
to the quantum analogous refrigerator?
- I think of a refrigerator as anything
that uses a resourceto cool down a system.
(46:36):
I'm working with Simone Gasparinetti's lab
in Sweden at Chalmers University
on building a quantum refrigerator.
It consists of superconducting qubits.
Superconductors are quantum systems.
They're little circuitsin which current can flow
for all time without ever dissipating.
(46:58):
Superconducting qubits are being used
as the physical systems
that encode basic unitsof quantum information
in many quantum computers.
Chalmers University isbuilding a quantum computer.
A superconducting qubitquantum computer needs
to be at low temperatures.
If the quantum computerhas just run a calculation,
(47:19):
then it's effectivelyfilled up its scrap paper.
These superconductingqubits act like scrap paper
that has been scribbled on.
They need to be reset.
They need to be, in a sense,
erased like scrap paperfor the next calculation.
They are reset if theyare cooled down even more.
This quantum refrigerator will be inside
(47:42):
of the preexisting classical refrigerator
that keeps all of thesuperconducting qubits
at a low temperature.
And the quantum refrigerator has the job
of cooling down theseused qubits even more.
The experiment is supposedto be happening right now.
We have numerical simulations.
(48:02):
We'll see how well those are born out.
- I've heard you talk about the fact
that the initial idea for oneof your research projects,
which I know has now been published
with a team of your collaborators,
first came up over an informaldiscussion over coffee.
And I think this type
of thing actually happens pretty often,
(48:23):
maybe more often than we might think.
It actually happened tome as well during my PhD
that a project that I endedup spending a lot of time
on came up over a discussion at lunch.
Although, I wasn't partof that discussion,
but I ended up working on the project
that resulted from that discussion.
I'm just wondering if you cantalk a little bit about that
(48:43):
and maybe what you think is so special
about those spontaneous discussions
that between researchers.
- This collaboration began during my PhD
when I was at Caltech.
There is a condensed matter theorist,
Gil Refael, at Caltech.
He has an office in abuilding called Bridge.
(49:04):
But most often I saw himat the Red Door cafe.
After lunch one day, Iwas at the Red Door Cafe,
he was at the Red Door Cafe, and he said,
"Hey, you're interested
in breaking the second lawof thermodynamics, right?"
Personally, I think that thesecond law of thermodynamics
probably cannot be broken,
but I am extremely enthusiastic
(49:26):
about the second law of thermodynamics.
So I asked, "What are youinterested in discussing?"
And he said, "There'sthis phase of matter,
many-body localization."
This phase was very, very popular.
It was undergoing a lot ofstudy when I was in my PhD.
Gil contributed a lot to that research.
He said, "We've been studyingmany-body localization
(49:48):
for a while now.
And it's interesting froma physics perspective,
but what is it good for?"
So many-body localizationis a phase of matter
of quantum many-particle systems.
The behavior of a many-bodylocalized system contrasts
with ordinary behaviorthat we might expect.
(50:09):
Let's go back to the example
of a classical gas in a box.
Suppose that we have aclassical gas in a box,
we measure its particles' positions,
and we find that the particlesare all clumped together
in one corner of the box.
Shortly thereafter,
the particles willspread all over the box.
(50:29):
They won't hang aroundin the same positions.
However, if we have amany-body localized system,
which could consist ofa bunch of cold atoms,
and we measure the positionsof these particles,
then those particles willapproximately hang around
in the positions fora long time afterward,
(50:51):
in contrast with the behaviorthat we would expect.
A many-body localizedsystem has some resistance
to the second law of thermodynamicsand the flow of time.
If we're thinking aboutthe classical gas in a box,
we know time is flowingif we're watching the gas
because we see the gasexpanding all across the box.
That's why we think ofmany-body localization as,
(51:12):
in some sense, resisting thesecond law of thermodynamics
a little bit, although, eventually,
the particles do spread out.
Many-body localization had been proposed
as a possible quantum memory
for storing quantum information
since things tend to stay put in it.
But Gil was thinking,
just as there areinformation processing tasks,
(51:34):
such as storing information,
there are also thermodynamic tasks.
So maybe I should ask aquantum thermodynamicist
what we can do with this resource.
We talked for a while,and we eventually brought
into the project two more collaborators:
Christopher White andSarang Gopalakrishnan.
We came up with theidea of a quantum engine
(51:57):
that can be changed
between this many-body localized phase
and a more thermalizing phase of matter
in which particles andinformation spread out quickly.
Many-body localization is a long name
that has very many letters and syllables,
so it's often called MBL.
(52:18):
Gil came up with a wonderfulname for the engine,
the MBL mobile.
- We've been asking youa lot about your book
and now about your research,
but I also wanna ask youabout something kind of
at the intersection of those two.
Can you tell us if writingthe book helped you at all
with your research?
- Absolutely. It was extremely helpful.
On the one hand, I had toextract the basic physics
(52:41):
from a lot of differentthermodynamic discoveries.
When I think of a highlycompetent theoretical physicist
whom I admire, I think of someone
who can explain a discovery
in terms of just the basic physical story.
That person knows what's really essential,
(53:01):
what's really important,
so they don't bog down the explanation
with a lot of unnecessary details.
I had to extract the basic physics
from discoveries in this way,
and that helped me understanda lot better what was really
behind these thermodynamicsettings and findings.
(53:23):
Also, I had to write at the end
of my book what I thoughtwas ahead for the field.
I started thinking fromquantum thermodynamics,
we've gained wonderfulfundamental insights.
Can quantum thermodynamicsalso be practical?
What would it take forquantum thermodynamics
to be practical?
The original theory ofthermodynamics went hand in hand
(53:43):
with the Industrial Revolution,
which was extremely practical.
It would be wonderful
for the quantum thermodynamic engines
and refrigerators and so on
that have been proposedto lead to utility.
I mentioned that experimentalists
have realized quantumthermodynamic engines.
(54:05):
These experiments are proof of principle.
They show that if we work really hard,
we can create and run quantum engines,
but we tend to have to invest more work
in cooling the engine downand in manipulating it
than we can extract using the engine,
which is quantum, so it'sjust a little bit of energy.
(54:27):
I thought about what we would really need
to make quantum thermodynamics practical.
I started thinking about solar panels
in Southern California.
My PhD advisor, John Preskill,
has solar panels on hishouse in Southern California.
He can use solar panels to great effect
because he happens to be in an environment
(54:48):
where they fit in and just dotheir own job very usefully.
If we were in Buffalo instead,
solar panels would not be so helpful.
I think of the quantum engines
that have been realized today
as kind of similar tosolar panels in Buffalo.
We have to spend a lot of work on them,
just as you would have to spend a lot
(55:08):
of work scooping snow offyour solar panels in Buffalo.
I started looking around
for a quantum thermodynamic context
for quantum thermodynamic technologies
that is, frankly, like SouthernCalifornia for solar panels.
Shortly after writingthat section of my book,
I got an email from Simone Gasparinetti,
(55:30):
the experimentalist that I mentioned
who I'm working with in Sweden.
I was not working with himat the time, but he said,
"I'm starting up a lab.
How about we chat
about what you thinkare great opportunities
for quantum thermodynamic experiments?"
And I said, "Recently, I've been thinking
about this need for aquantum thermodynamic setting
that's like SouthernCalifornia for solar panels.
(55:51):
I want to make quantumthermodynamics useful."
I should also mention I'm not
the only quantumthermodynamicist who would like
to make quantumthermodynamic devices useful.
There are other peoplearound the world thinking
in this direction, butI'm just telling the story
of how I came to this direction
and this collaborationand this experiment.
And Simone said, "Ah,I have such a setting."
(56:12):
And so we embarked on this adventure
of developing a quantumthermodynamic refrigerator
that we wouldn't have to spend a lot
of control on in operating,
that would just do its own thing
to reset qubits aftera quantum computation
in a superconducting qubitquantum refrigerator.
(56:33):
So the book has absolutely been useful
for my physics research.
- To follow up on that,
are there any sort ofbig-picture breakthroughs
or advances in your field?
That, you know, you're stillquite a young researcher
with a long runway ahead in research.
Are there breakthroughsthat you hope you'll see
or even make in your career?
(56:54):
- I am very fascinatedby this growing subfield
that I mentioned before
that involves incompatible properties
of quantum thermodynamic systems.
There are a lot of reallyfundamental questions
that haven't been thought about.
For instance, to what extent does
the small system reachthermal equilibrium?
(57:15):
Also, I think there arereally interesting discoveries
to be made when we take this idea
and bring into other fields.
For instance, the last timeI was in Santa Barbara,
I went to a many-body physicist.
There is toolkits inmany-body physics called,
it also has a horrendously long name,
(57:36):
the eigenstate thermalization hypothesis.
It helps us understand whyquantum systems thermalize.
Why, in some sense, time flows
for them in some ways similarlytoo for classical systems.
This many-body physicist in Santa Barbara,
Mark Srednicki, callshimself the high priest
of the eigenstatethermalization hypothesis.
(57:59):
He was one of the people
who helped create this toolkit.
It's very powerful.
It has been transformativefor quantum many-body physics.
It's been used an enormous amount
over the past few decades.
And I asked, "What if we try to apply it
to a system that has theseincompatible properties
that are being exchanged?"
And he said, "You know, Ihadn't thought about that."
(58:21):
And it turns out that thistoolkit needs to be changed.
This toolkit that has beenaround for many decades.
I think that there are othersuch realizations waiting
to be had in this subfield.
- You've been so generous with your time,
and you have a conference to get back to.
Thank you so much forsitting down to chat with us.
It's just been a pleasure.- Thank you again
for having me on the podcast.
(58:41):
It's really been a pleasure.
(upbeat music)
- Thanks so much for listening.
Perimeter Institute is
a not-for-profit charitable organization
that shares cutting edgeideas with the world thanks
to the ongoing support
of the governments of Ontario and Canada,
and also thanks to donors like you.
Thank you for being part of the equation.
(59:02):
(upbeat music)
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