(gentle music) - Hi, and welcome to Conversations at the Perimeter. Today, Colin and I are excited to share with you our conversation with Tim Shay. Tim is a research faculty member here at Perimeter Institute to for Theoretical Physics. And his work is at the intersection of quantum information and quantum matter.
- And it was such a fascinating conversation to have with Tim 'cause we talked not only about quantum matter and quantum science, but we talked about his childhood, growing up in Los Angeles, and competing in the physics Olympiad and coming to Perimeter Institute as a teenager for the International Summer School for Young Physicists. And we also got into his newest adventure, which is fatherhood. So it was a fascinating conversation about science, life, and just about everything.
- I know, you're all gonna enjoy this conversation. Let's step inside the perimeter. Tim, thanks so much for joining us today. - Yeah, sure, my pleasure. - So I wanted to start by asking you a little bit about the area you work in, in your research. I was reading that your work is at the intersection of quantum information and condensed matter. So I'm curious what draws you to that specific intersection and why you like to combine those two fields?
- Basically I'm most interested in what happens when you have, like many quantum degrees of freedom that are all kind of interacting with each other and what type of new phenomenon can arise from such a big system? You know, it's kind of different from the usual philosophy of physics, which has basically been like a reductionist philosophy where we start with the big universe as a whole, right?
And then we try to break it down into smaller building blocks, like our atoms into electrons, protons, neutrons, and then even smaller pieces. You know, that has had crazy amount of success culminating in the standard model. But this other philosophy of looking at this emergent approach of physics is kind of like the other way around. Like we know the basic building blocks, let's say we have some electrons.
And then now the question is not trying to reduce it further, but trying to put them all together and see what types of new physics can arise from this collection. Not reducing, but building up from the bottom up. - A colleague of mine wrote an article about you. And she said it was like a quantum form of Legos. - Yeah, yeah, exactly. - That metaphor that we're starting with individual building blocks and then seeing what we can build out of it. - Yeah, yeah, that's right.
- I have to ask, were you a Lego kid? - I was, I was a big Lego fan. - Were you building complex objects out of simple building blocks even then? - I was most definitely throwing away the manuals and just trying to do things myself. That's indeed what draws me to this approach to physics, because it really allows you a lot of freedom of creativity to try to engineer all sorts of new phenomenon that you would never have expected just by looking at each piece individually.
- How does quantum computing factor into this or quantum information? - So quantum computing you can think of as a large collection of these degrees of freedom called cubits, which you can realize physically in many different ways. So a quantum computer would be an example of such a big collection of quantum degrees of freedom that we are manipulating in a way to perform useful things.
A quantum computer, you can think of it as a particularly useful phenomenon emerging from this large collection of quantum particles. - Are you also interested in some not so useful products? - Yeah, it depends on what do you mean by useful. And as a physicist to me, one of the most appealing applications of quantum computers is to simulate quantum systems that if we didn't have a quantum computer, it would be hard to simulate.
So basically using our classical computers, we would struggle with understanding. There are a lot of intractable models that we run into problems either with pen and paper or with our current computers. However, if you had a quantum computer, you would be able to simulate these intractable models, do measurements on your quantum computer to read out answers that you would not have access to.
So it's that type of not so practically useful on a day to day basis, but as a physicist, very meaningful. - And I guess of course, if something is not useful immediately, it doesn't mean that it couldn't be useful some- - That's right, that's right. - It could be useful. - Yeah. - Another question I have 'cause you started talking about simulation and can you help us understand that word? And also maybe what's the difference between a quantum computer and a quantum simulator.
- A quantum computer is kind of a all purpose device, So the idea is that you have some quantum particles that you can carry out operations on and you can carry out like a arbitrary operation. It's kind of like our current classical computers. You can pretty much carry out any algorithm you want on your current computer.
However, a quantum simulator, maybe you can think of as a more restricted version of a quantum computer, where you don't have full access to all possible operations, maybe only a subset, but that subset of operations may still be something beyond the current reach of classical computers. For example, in condensed matter, there are these famously hard models to solve like a Hubbard model, which is supposed to just the phenomenon of high temperature superconductivity.
these particular models that can be implemented in quantum simulators. These simulators cannot do everything, but they may be able to implement specific models that we can still learn from. - You mentioned just now high temperature superconductivity. I hear that mentioned a lot around quantum matter and quantum materials. Could you explain a bit about what that is and why it's a goal that we're chasing. - Superconductivity is a very well known phenomenon in condensed matter physics.
It dates all the way back to, I think 1911, it's a fascinating phenomenon to which basically the resistivity of the material drops to zero below like a certain temperature. - Is that a resistance in terms of like carrying electrical current? - Yeah, that's right, that's right. So you could pass current through this superconductor without any dissipation, without any like energy loss. - Without a superconductor, much, much energy is lost. - That's right.
So, you know, like when we pass current through typical metals that, you know, are not superconducting, there's heat loss, and that's a major problem for like energy transport. - Superconductivity is possible, but at super low temperatures. - Exactly, so they're actually not super low at this point, they've gotten higher and higher as the years has progressed, but they're still relatively low on everyday human scales. They're on the order of several Kelvin, usually. - That seems extremely low.
- That's right, but- - But this is the difference between everyday scales. - Yeah, yeah, exactly, right. And so the holy grails to have like a room temperature superconductor, where you wouldn't have to bring in a doer of liquid helium to cool down. You could just operate that at ambient environment, and that would clearly be very useful. - It'd be useful for energy transmission? - Yes. - I've seen the superconducting levitating. - Yeah, the maglev trains. - Right. They use it super cooled?
- Presumably the temperature they need is still pretty low. - Why is it such a challenge to achieve superconductivity at higher temperatures? - I don't think there's any like known recipe at making this critical temperature higher and higher. Like it's a very complex phenomenon. The models of superconductors with relatively high temperature, people can write it down, but making analytical or even numerical progress on it is hard, right.
So if we can't really tackle the models, it's hard to understand why certain materials have higher TC than others. And so it's hard to engineer higher TC. - You said that it's sort of a holy grail. That the technological offshoots of high temperature superconductivity could yeah, have all sorts of effects in practical life. What about it in your specific research area? What are the specific challenges that you are tackling in quantum matter?
- I've been very interested in this feedback loop between quantum materials, which might be useful for building quantum computers and then using quantum computers to understand those quantum materials better. You may think of it as a bit of a chicken and egg problem. But the hope is that, you know, some quantum computers might not require such quantum materials to build. Like there are many different approaches at building quantum computers.
And so then given, you know, a functional quantum computer, like what can we do with it to learn more about these quantum materials that we have trouble understanding. I'm interested in both directions, right? Like how can we leverage existing quantum matter to build these things, and how to do interesting things on these quantum computers to learn about quantum matter.
- And I think a lot of people can find it confusing when we start talking about quantum computing or quantum simulations, because for certain things, we actually need to have a quantum computer, but then there are some properties of quantum systems we can actually study on a classical computer. - Yeah, indeed. It turns out that for some approaches of quantum computing, there are some operations that are relatively easy to carry out.
However, it turns out that one can simulate those operations on a regular classical computer already. That's why it's so important. It's so important for the field to establish the notion of quantum advantage, where a quantum computer can do something, you know, beyond the capabilities of a classical computer. But this is a very subtle question because we don't know for sure some of the boundaries of classical computing itself.
Like for example, even like factoring a large number, we believe it's a very hard problem just based on our experience, like, we don't have any good classical algorithms to do that. But proving that it's really hard is not that easy either. - Proving that nobody will ever come up with a good way of doing that. - Yeah, that's right, that's right. So there's this interesting interplay between, kind of pushing the boundaries of our classical approaches.
Yeah, like pushing the boundaries of our classical approaches until they reach what a quantum computer is able to do. And this boundary is very mysterious at this moment. It's not very well defined at the moment. - Are there some problems, maybe the boundary is hard to define, but are there some things that are clearly on one side or the other?
- Yeah, so as I was saying before, there are some operations that are relatively easy to do on some quantum computers that we can simulate on our classical computers. It turns out that kind of upgrade these operations to a fully universal mode in which the quantum computer can do everything. It turns out to do that, we need this resource called magic, which is, you know, actually a technical term in quantum information. - I love it, I love that there's a technical term.
- Who came up with this term? - Ah, I think originally it was Sergey Bravyi and Alexei Kitaev. You can think of it as like a resource, so some special quantum states that if your quantum computer has access to, then it can really do everything. You can carry out operations like well beyond what our classical computers can simulate. - Is this still largely theoretical work or is it beginning to turn into technological achievement? You know, are we building quantum computers?
You mentioned the example of factoring large numbers, that's the example I often hear, a problem that classical computers struggle with, but quantum computers, thanks to, was it Shor's algorithm 20 something years ago, that maybe a quantum computer could do this. And can you explain some of those challenges that we think quantum computers will be able to tackle and those that might maybe in the realm of classical forever?
- The problem I mentioned of factoring large integers, that that's one famous example of what a quantum computer can do efficiently, but that a classical computer can do inefficiently. I think other examples of, you know, where we can get a major quantum advantage are in quantum simulation. Like looking at the dynamics of a quantum system, of like a many body quantum system. It's typically hard to simulate such things on our current computers.
But for quantum simulators, you just have the thing right there and you just let it evolve in time. It itself is the object of interest, right? And so you just read out whatever you want to know about it from this system itself. - And so are you working largely theoretically and you're working with experimentalists? how does it work in terms of going from pure theoretical ideas to possibly a device?
- I guess what I've been doing in the past couple years is proposing some interesting protocols that can be carried out on existing quantum computers, that are in the spirit of this quantum simulation. So basically in condensed matter, we have many interesting states that we have yet to realize in actual like solid state quantum materials. And yet now with these quantum devices, you can imagine just building these states directly, as opposed to having to find it in like a piece of rock.
- I hear states, my layman interpretation is liquid, solid, gas. Am I right in thinking that that's just the tip of the iceberg when you... - Indeed, that that's a good analogy. So liquids and solids, these are examples of classical phases of matter. You can think of them as states that are robust to some imperfections, right? So for example, like a solid, if you tune the temperature a little bit, it's still a solid.
Or a liquid or gas, if you tune the temperature a little bit, it's still the same phase of matter. There's some degree of robustness implied by the definition of phase. On the flip side, you can have phase transitions between them, like, if you tune the temperature too high, you know, you can have a solid to a gas transition.
What we deal with is quantum phases of matter, where again, you have some degree of robustness implied, but now the tuning parameter is no longer temperature, but some extent of quantum fluctuation. So you can have like zero temperature quantum phases of matter that are tuned from one phase to another, not by temperature, but by some parameter in your system that controls quantum fluctuations.
- So I guess superconductivity would be an example of- - Exactly. - Of these quantum phases are there other examples? - So for example, you could think of like a ferromagnet and paramagnet as two different quantum phases of matter. So basically, you know, you can imagine that your system is some collection of magnetic moments. In one phase, the ferromagnetic phase, they all align. Whereas in the paramagnetic phase, they're all disordered and highly fluctuating.
So that's another example of quantum phases. - Do some of those quantum phases have this quantum magic that you were talking about? - Yes, yeah. One thing we did recently was basically connect this concept of magic, this resource that you need to upgrade your quantum computer to be fully universal. What we did was connect this magic resource to the study of quantum phases of matter.
So my collaborators and I found that certain topological phases of matter are guaranteed to possess this resource magic. - And what's a topological phase of matter? - Yes, thank you. - Yes, that's a good question. So a topological phase of matter is kind of an unusual quantum phase of matter. So the example I gave earlier of quantum phases of matter, this ferromagnet, is something with like a local order parameter.
It's something where if you look locally at the system, you see that all your magnetic moments are aligned in a particular direction, right? So it's something that you can identify locally. However, a topological phase of matter is still distinct from a completely disordered phase, the paramagnet, but it cannot be identified by such local order parameters.
You need to look at some more global property of the system, for example, some entanglement property of the system or some property of the boundary of the system, it's that, that distinguishes topological phase from the paramagnet - Is it really sort of parallel to the idea of typology, thinking of the, you know, the shape of the mountains and valleys of the earth? You're looking at something in a broader picture rather than an individual...? - Yeah, yeah, exactly, exactly.
The idea behind typology is that you have some robust property of the system, that any local deformation cannot change. So, you know, you have like a torus, but if you like pinch it locally, it's still a torus. And so it's that kind of global notion that characterizes a topological phase as opposed to a local order parameter, as in the ferromagnet. - You're a co-leader of the Clay Riddell Center for Quantum Matter at Perimeter.
Can you explain what that is and what you and your colleagues sort of broadly are trying to do with quantum matter here at Perimeter? - The Center for Quantum Matter is kind of built from the foundations of three fields. I would say quantum materials, quantum information, and quantum gravity. These fields actually have a lot in common.
All of us are pretty much interested in this question that we be began the podcast on, which is what happens when you put many quantum degrees of freedom together and allow them to interact strongly? Like what can come out of this many bodied quantum system? And it's this underlying question that kind of drives all three of these areas of our center.
- So a truth about quantum gravity, about what happens in extreme gravity could relate to building a quantum computer, there could be parallels there? - Yeah, I think more specifically in quantum gravity, there's this notion of holography where a strongly interacting many bodied quantum system is actually equivalent in some sense, to a theory of gravity in one higher dimension. And so there, it's a very striking phenomenon of gravity that has emerged from this many body system.
But gravity is just one extremely interesting instance of something emerging. - Gravity is considered an emergent phenomenon in... - Yeah, from this picture, yes. - The result of many, many smaller, complex... - That's right. And so that may give you some insight into how ideas from quantum information can be used to shed light on this holographic correspondence, and similarly ideas in quantum fruition shed light on quantum materials for similar reasons.
- That's amazing to me that think that people who are examining how the universe works on the largest scales, you know, the quantum gravity theorists have a common language with people who are... - That's right, that's right, yeah. - Ion traps or other quantum computing devices. - Right, right, exactly. - Really connects the huge to the small. - These three areas that have this philosophy in common, that the center is built on.
So it aims to facilitate collaborations between these three areas and make progress. - Would they typically connect to each other or is that the point of the center, to make them find those? - I would say in the past decade, there's been more and more momentum in kinda unifying these three areas. And the Center for Quantum Matter is kind of like, yeah, it's like a reflection of all this momentum toward unification.
- I wanna go back to asking you something about this paper that you mentioned on magic. I think it's called symmetry protected sign problem and magic in quantum phases of matter. I took a look at this paper before our discussion today, and I couldn't help but notice that the word symmetry comes up a lot in the paper. So actually just in the first sentence of the abstract, it's there three times.
So the first sentence is we introduced the concepts of a symmetry protected sign problem, and symmetry protected magic to study the complexity of symmetry protected topological phases of matter. So can you tell us a little bit about symmetry and how that plays a role in quantum matter or maybe specifically in this work? - Yeah, I think symmetry has played a fundamental role in quantum phases of matter from the very beginning.
The first example I mentioned of this, this ferromagnet versus a paramagnet, that's an example where one of the phases has broken asymmetry. You know, I was talking about this system where you have many local moments. In one of these phases, the symmetry is preserved. Like if you rotate these local moments, nothing happens. However, in the ferromagnetic phase, in which they're all aligned, they've spontaneously picked out one direction. So the symmetry, this ability to do a rotation is broken.
- The symmetry, essentially, like no matter which way you turn something, it's the same. - Exactly, so symmetry, the principle of symmetry and symmetry breaking has been a key concept in just even defining different phases of matter. It's only until recently that people have started thinking about topological phases of matter, which are not necessarily characterized by symmetry breaking anymore.
And so that's why they're characterized by more complicated things like entanglement or phenomena at the boundary of the system. However, symmetry has continued to play an important role even in these topological phases of matter. And that's because of the discovery of these things called symmetry protected topological phases. These topological phases of matter are characterized by some interesting phenomena at the boundary of their system.
There's these things called topological insulators, whose bulk properties are insulating, and yet their surfaces conduct, so they're metals. What make this non-trivial phases of matter is this connection between this metallic boundary and the bulk insulator. These are symmetry protected in the sense that if you break the symmetry, then you lose this property of the metallic boundary.
That's why it's symmetry protected because to maintain this correspondence between this metal or the boundary, you need to preserve the symmetry. - And how do you make sure that you preserve a symmetry? - In practice, you never strictly preserve it. It can be weakly broken. For example, in these topological insulators, they're protected by time reversal (unclear). Earth's magnetic field, you can't really turn off, but it's very small.
And it turns out that it's so small that its effect on breaking these nice properties is very small. If you can respect the symmetry, within some small error, you're fine. - As a nonscientist myself, I'm fascinated by this, but it's making my brain throb a little. So I wanna go back a little bit and just ask, like, how did you get into cutting edge stuff? How did you find your way into doing this for a living?
- As a young kid, I was very interested in just problem solving in general, from Legos, or just, you know, some small like physics or math problems. And I think that's what motivated me enough to learn about the basics of physics. It's really just a drive to understand everyday phenomenon at the most basic level. - Was that always a drive for you? Were you always looking around saying, how does that work or what is this?
- I think it was that Lego philosophy of just first going down to the most basic building blocks before like assembling it all together. - What is the most complex structure you built with Lego? - There were some crazy spaceships, that's yeah. - You grew up in Los Angeles, right? - Yeah, that's right. - I think most people have a picture in their head of what Los Angeles is, 'cause of pop culture, we all know. But can you tell us what was Los Angeles like for you to grow up in?
What were you doing as a child in Los Angeles? - One of the most appealing features of LA as a kid was the musical elements. I started violin at a very early age and performed solo violin and chamber ensembles and orchestra, LA was just great for that. - You started out in like youth orchestras in Los Angeles? - Yeah, yeah, exactly. - You're being humble, you haven't mentioned yet that you've played Carnegie Hall.
- My orchestra fortunately had the opportunity to go to Carnegie Hall when I was in high school. And so that indeed was a wonderful experience. - Were you interested in physics at the time or was it all music first and then you discovered science later? - I was definitely interested in physics at the time. So that same year that we went to Carnegie, I had the other good fortune of competing in the US Physics Olympiad.
And there, I made it to this national training camp, that was another, I think, major milestone. - I'm so curious. I've never seen a Physics Olympiad. In my head, I'm picturing physicists running around a track and doing high jump, but I know that's not it. What are the challenges that you do as a kid at a Physics Olympiad and how did you approach it? - It's very similar to the usual athletic competitions, except everything is in your head. - I like.
- Whether or not it's fun, this is another question, I guess. Well, yeah, it's basically just a lot of problem solving of very, very interesting questions in classical mechanics or electromagnetism. - And there's various teams and whoever gets the most right answers or does it the fastest, how does it work? - Back then, like speed was not the problem. You have like several hours to work through these problems.
At the of the day, it is a competition, I think, between various different countries, basically who can solve the most problems most completely. - And you were how old at the time? - My junior year of high school, I think probably around like 14, 15. - Okay, you got to compete nationally? - Yeah, that's right, that's right. - Do you remember what kind of challenges you were faced with? - That was the first time in which I saw how smart people can be.
So as you grow up, you're only exposed to so many people and yet on this national stage, you really see like how skilled people can be, like how fast they can think, how well they can think. And that to me was really a humbling and exciting experience. Because it really sets a bar that you can aspire to. - Are you still in touch with anyone from that time or did any of them go on to be...? - Yeah, yeah, I know several people on the team, I've kept in touch with them.
Some have become experimental physicists, some have gone on into it to other fields like applied mathematics. We've all gone our different ways, but I'm sure that training was very useful, no matter which discipline. - And shortly after that was when you first came to Perimeter for the International Summer School for Young Physicists. - Right, right. - Can you tell us a little bit about that and maybe what stands out when you look back on time.
- So at the culmination of this Olympiad training camp, they advertised, a relatively new program at Perimeter. ISSYP, it sounded great. The summer after I graduated high school, I attended ISSYP. And I think that that was the first time in which I really learned some basic concepts in quantum mechanics. - After all those Physics Olympiads, those were more... - All the Physics Olympiads were primarily classical physics, mechanics, and ENM.
I only had some vague notions of quantum mechanics at the time. ISSYP really opened my eyes further. And, you know, allowed me to really see some of the counterintuitive aspects of quantum mechanics. - Plus I assume you were there with other teenagers who were sort of just like you, had been probably doing their own physics contests and physics enthusiasts. I imagine you were surrounded by sort of like-minded individuals. - That's right, that's right.
- You remember what that experience was like as a teenager to come to Canada and meet these new people and spend a couple weeks just immersed in physics? - It was really great. I think at the time, probably even now at the ISSYP, they break the group into several smaller groups that can work together, work through these hard problems in quantum mechanics or otherwise. And yeah, I distinctly remember many of these team experiences that were really fun.
- So you came here in high school and now you're here at Perimeter - Right, right. - A Faculty member, what happened in between, what are some of the milestone steps that kind of, you went, you took until you... - Well, I guess the short answer is I learned a lot more quantum mechanics, to the extent that I was able to actually use it in a constructive way. - One of the leaders of the Quantum Matter center now. - Right, right, right.
- When you got that first exposure to quantum science and quantum mechanics, what did you think of it? These concepts are not terribly intuitive. - It's just very exciting because our day to day experience are consistent with classical physics.
And so these counterintuitive ideas of like entanglement, superposition in quantum mechanics are just something that you can almost think of it as like a dreamland, as like a, it's not an alternative universe, because it describes the microscopic nature of our current universe, but it's so different that it's almost like going to a different universe and playing around there. So that's what really fascinated me. - I like that. And your enthusiasm talking, I can tell you enjoy this stuff.
- Yeah, yeah. - You light up talking about quantum superposition and entanglement. Are you still sort of fascinated by it? Is that what keeps you going? - Yeah, I mean, the thing is if you think really deeply about quantum mechanics and its foundations, eventually you realize that philosophically, it's not that complete yet. - Is that why it's so counterintuitive to us 'cause it's not yet complete or because we haven't developed our intuition for this stuff yet?
- Well, I think even things that are, you know, solidly in the foundation of quantum mechanics are already counterintuitive, but there's this additional aspect that the theory, even while being counterintuitive, is not like aesthetically that satisfying at times.
So for example, in basic quantum mechanics, you first learned that there are two types of operations of just the unitary evolution of a system and measurement, and these two things, in your most basic course, you learn that they're just two separate operations that are allowed in quantum mechanics.
And later maybe in a more sophisticated course, you learn that this idea of measurement can be incorporated within unitary evolution of a bigger system in which you treat the object of measurement and the measuring device as a joint system. - Talk a little bit more about measurement here, because I think it's a word that a lot of people would use pretty often, and they're using more of a classical definition.
So why is measurement maybe more subtle or what are kind of some of those subtleties when we're talking about it in quantum mechanics? - Yeah, measurement is subtle in quantum mechanics because in quantum mechanics you can have basically a superposition of many different states. And when you do a measurement in the most basic description, you're collapsing that big superposition into one branch of the superposition, into one component of it.
That's why, again, in a most basic description, this measurement is some operation that supplements the usual dynamics of the superposition. You know, our superposition, it's supposed to evolve under a Schrödinger equation. And yet to describe the actual measurement process, you need to say, okay, there's this weird operation where it can also collapse into one component only.
And so it's this tension between these two types of operation, this coherent evolution with Schrödinger equation, and this drastic that collapse to one component, that is very subtle. How the two can be reconciled, if at all, I think is still a open question. - Measurement means that it causes that collapse to it. - Yeah, yeah, right. - You can't look at a superposition, once you look you've forced it to... - That's right, that's right.
The kind of paradox is that your measuring device, and the thing being measured are just also some big collections of particles, that are evolving under the laws of quantum mechanics. So in principle, they should just be evolving under the description of the Schrödinger equation. So then why did I need to introduce this extra concept of collapse? It's this type of subtlety that is quite fascinating.
- And I know some of your work involves even now exploring some of the subtleties of this measurement and you're looking at these quantum systems, these large quantum systems, you can do these measurements on maybe different parts of the system, or you could do it at different rates, very often, or maybe spread apart. What are some of the interesting dynamics or features that you can observe by adjusting how you measure?
- Yeah, so indeed what we were discussing about the more philosophical aspect of measurement, one can just kind of sweep it under the rug for now and adopt the shut up and calculate philosophy of quantum mechanics, right? Where you just accept it as the way it is and kind of run with it. And indeed, that's what I, and many other condensed matter physicists have been doing.
What we were doing is kind of motivated by recent use of measurement as not something you do at the end of an experiment, but as something you can do during the experiment to create some interesting dynamics. As I said, you can think of quantum mechanics as having these two operations. One is unitary evolution with Schrödinger equation, and one with measurement, these collapse of the wave functions, right?
And so previously most of the dynamics we considered only involve one kind, this Schrödinger equation evolution. However, when you put the two together, it turns out that you can have very interesting dynamics leading to dynamical phase transitions. I've been very interested in recently is exploring this dynamics involving both of these operations. And these operations kind of want to compete with each other.
So this Schrödinger equation evolution or unitary evolution, it tends to want to create entanglement. It wants to entangle many particles together. Whereas this measurement operation, it wants to disentangle particles and just collapse things locally to definite states. So there there's this competition between entangling dynamics and disentangling dynamics.
At a critical balance between the two, you have this phase transition, and it's this type of interesting dynamics we've been playing around with. - And so one of the phases on one side of that transition would have more entanglement and the other one would have less. - It's not even necessarily the amount of entanglement, it's how the entanglement scales with the system size. So basically in one phase, the entanglement is very short range.
If you divide your system into two pieces, you only have entanglement locally across the partition. However, in another phase the entanglement is long range. Across the partition, you have entanglement between particles on all scales. - You sort of joked that when you finished ISSYP here at Perimeter, and then came back later, in between you just learned a bunch more quantum mechanics.
I think that's a nice way of saying that you did a lot of schooling, you went to MIT for your PhD, and a postdoc at Kavli Institute in California. I want to focus on the MIT bit for a second because I discovered a very interesting, cool connection between your musical life and your scientific life. Can you tell us a bit about this composition? Let's actually just play a little bit and then tell is what it was. (violin playing) So that's you on violin.
- Right, that's the Bach. One of my friends at MIT figured that this is a very nice piece of music to juxtapose with one of Frank Wilczek's lectures. - Frank Wilczek being the Nobel prize winning physicist. - That's right, that's right. I think that year I had been taking a reading course with Frank in the Center for Theoretical Physics. I should've realized that it was pretty cool to put this together with Frank's lectures.
- Yeah, it's this beautiful collection of footage of, it looks a lot like Perimeter actually, because of the close ups of chalk on a blackboard and people in a classroom, all the while it's you playing violin in the background. It's this beautiful combination of art and music. I encourage everybody to Google it, to find it on, I found it out in Vimeo. What did you get out of doing that?
- Well, I think it just made a lot of sense to me because I think both music such as Bach and quantum mechanics, they're all these beautiful structures, these beautiful rules that kind of reflect each other. - I can sort of see that. Have you found that doing one helps you do the other, doing music and science sort of go hand in hand? - As a kid, I definitely found that performing music by practicing, I definitely developed the discipline and concentration to do physics well.
I guess at that practical level, there was already a connection when I was a kid. Now I just view one as like a way to escape the other when I get, you know, really tired of doing one. - Well, in that way, they'd be complimentary as well. - Yeah, yeah. - Yeah, that's interesting. I hadn't thought that they both were based on sort of their own language and their own rule book. - And I guess it also goes back to this philosophy of emergent phenomenon.
Because you know, in music you have notes, right. You have these basic notes, chords, right, and the way you put them together, you can get stuff you really wouldn't have imagined before. - You can put notes together and you get chaos and noise. - Yeah, yeah. - You can put it together enough harmony and melody and... - Right, right, right. - And that chord that comes up is quite different than just playing each note one at a time. - Exactly, exactly.
- Music is an emergent phenomenon. I like that. - Yeah, yeah, that's right. - Well, Tim, we also ask for questions from some students or some listeners. So we have a couple that were sent in. The first one is from a student here in Waterloo. - This is Matt Duchene, a student at IQC and Perimeter. I'm wondering what has been your most memorable moment of your career so far, maybe either something that's happened to you or a breakthrough or a lecture or something that you've witnessed.
- So the question is what is the most difficult? - Most memorable. - Oh, most memorable. - It could be memorable because it's difficult. - That's true, that's true, that's true. I would say the most memorable moment was my time at the Kavli Institute as a postdoc. Those three years as a postdoc at KITP were probably the most influential in my career, I feel. Allowing me to get the confidence to tackle problems that I formulated and can solve on my own.
It was also just the environment at Kavli with all these people going through, the fantastic conferences they had, the brilliant postdocs and faculty there that really made for a very intense and gratifying experience. - Is that where you felt sort of you transitioned from student to scientist? - Yeah, yeah, exactly. Presumably that's true for many postdocs, you know, that's precisely the period in which that transition occurs.
But for me, the KITP was particularly special, I think, due to it's unique conference environment, I guess Santa Barbara is great. - Yeah, not too far from your home. - Yeah, yeah, that's right. - Santa Barbara's a nice place to do some physics. You can do just about anything probably. - Yeah, yeah. - I've also often thought that beginning a postdoc must be very challenging.
I guess it's exciting, but also challenging, because as a PhD student, you have an advisor that can maybe help you decide what problems to work on. And then as a postdoc, it's really, you have to become much more independent. Was it difficult to choose what to focus on in your postdoc? - Yeah, it was definitely pretty challenging just trying to survive on your own, floating in the open sea.
But I think what helped me the most was just having these other postdocs around that were great to talk to, bounce ideas off, give feedback on, it's that environment that was really special. - And then what drew you back to Perimeter to continue your career after the postdoc? - Perimeter and KTP actually have a lot in common, weather not withstanding.. But in terms of the philosophy and activity, it's quite similar. Perimeter also has a great throughput of visitors, at least before the pandemic.
This idea of having all these conferences in different areas, that you can just listen to, that are well outside your own specialty was also one of the most appealing factors. The other thing is just the spirit of Perimeter seems to be to tackle very fundamental problems in unique ways, that other people haven't even considered. And I think that that approach of doing physics that also drew me to here. - And also combining people maybe from different areas like you were saying.
- Yeah, yeah, that's right, that's right, all branches of theoretical physics. - You've recently started to tackle another very challenging, let's say another big challenge, fatherhood. - Right, right. - How is that going for you? - You know, I think from that point of view, the physics is actually very easy, You know, physics, at least there's some predictable laws that you can use to calculate.
But yeah, for fatherhood, it's at the same time, you know, very tiring, but also very exciting, in part due to this unpredictability. You have this complex many body system that is just absorbing and emitting information that... Yeah, it's just, you know, impossible to predict. It's also at the same time, like fascinating. - Does it help you see your work or life or everything through a different lens?
- Yeah, I think having a kid has definitely motivated me even more to think outside of the box. This baby is just, you know, again, taking in all this information in her own way and trying to make her own sense of this mysterious world out there. And I think it's this kind of first principles approach at looking at the world that helps one make very original research progress. So I think this has definitely motivated me to think even more outside the box and be more creative.
- And Tim, we have one more question. This one was sent in by Nayeli Rodríguez Briones and she's a postdoc at the University of California Berkeley. She wrote in this question, she asked what has been the most surprising or intriguing result that you have obtained in your research so far? - Something I did while postdoc at KITP, this is basically a way to kind of upgrade a phase of matter by coupling to auxiliary system. In phases of matter, you can have various degrees of complexity.
You know, I mentioned these topological phases of matter, but there are different degrees of how exotic that phase can be. So for example, there exists things like topological insulators already in real materials, like bismuth selenide. These, I would say are the slightly less exotic version.
However, there more exotic versions where you can have this phenomenon of fractionalization where individual degrees of freedom fractionalize into excitations that gain a life of their own in this weird phase of matter. And so what we found was like a way to kind of upgrade from the less exotic to this more exotic fractionalization by just coupling to a auxiliary system. - And was this different than what you were expecting to find when you started working on this project?
- It kind of arose from an earlier project of mine, in which I found that if you just couple a topological phase of matter to same degrees of freedom, you can kind of clone that phase. Like you can kind of duplicate it in the auxiliary system. We call this topological proximity effect. You're kind of inducing the order on a nearby system.
This work dimension before this upgrading of the phase arose and we realized that if you couple to different degrees of freedom, you can actually kind of clone it in a very different way. You can impart the non-trivialness of the first system onto the second one, but twist it in a more complicated way and make a even more intriguing phase of matter.
- It seems exciting to be doing all these things because you're doing them essentially for the first time, it's uncharted territory, you're combining things, and then looking for something that nobody's seen before. - Yeah, yeah. - There's a nice exploratory element to that. Does it keep you curious and keep you energized because you don't know exactly what's gonna....? - Yeah, yeah, definitely, definitely. I think that that's, you know, part of the whole, the beauty of quantum mechanics, right?
You have this space of possibilities that's exponentially large. There are all these possibilities out there. Many of them that are probably not terribly physical, but a large portion are surely physical. And we have yet to reach those portions of space. So that definitely keeps me going, this wide space of possibility. - Your enthusiasm really comes across, it's so fun to talk to people who are working on things that I don't fully understand, but I can see that they just love it.
And that there's so much possibility there, that you're always exploring something new, it's fascinating. - Right. - Tim, Well, thank you so much for sitting down with us today, this has been really fascinating and it- - Yeah, thanks. - And really a pleasure to talk to you. - No problem, my pleasure. (upbeat music) - Thanks for stepping inside the Perimeter. Please, help us out. - You can rate, review and subscribe. - And please be sure to tell two friends.
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