S2E12 - Quantum Thermodynamics with Jake Xuereb

How is quantum information connected with thermodynamics, and what can it tell us about the inner workings of quantum computers? Take a listen to Season 2, Episode 12 of insideQuantum to find out!

This week, Jake Xuereb, a PhD student at the Technical University of Vienna, tells us all about his work in quantum thermodynamics and the deep links with quantum information and computing, as well as the importance of geographic diversity in science.

Jake Xuereb obtained his Bachelors degree from the University of Malta, followed by a Masters at the University of Malta with visits to University College Dublin and Trinity College Dublin, and is now a PhD student in the group of Marcus Huber at the Technical University of Vienna.

Transcript

🟢 Steven Thomson (00:06): Hi there and welcome to insideQuantum, the podcast telling the human stories behind the latest developments in quantum technologies. I’m Dr. Steven Thomson, and I’ll be your host for this episode.

(00:16): In previous episodes, we’ve talked a lot about how quantum information underpins quantum computing, communication and cryptography, but increasingly, researchers are beginning to use the language of quantum information to describe all sorts of other phenomena in many-body physics and thermodynamics and gain a whole new insight into fundamental processes that seem at first glance very different from quantum computing. Today’s guest is putting these building blocks together and working on the quantum thermodynamics of computation itself. It’s a pleasure to be joined today by Jake Xuereb, a PhD student at the Technical University of Vienna. Hi Jake, and thank you so much for joining us today.

🟣 Jake Xuereb (00:54): Hi Steven. It’s my pleasure to be here.

🟢 Steven Thomson (00:56): So before we get into the details of your work on quantum thermodynamics, let’s first talk about your journey to this point and, as is, tradition, let’s go right back to the very beginning. What first got you interested in quantum physics?

🟣 Jake Xuereb (01:08): That’s actually a very straightforward answer for me. I remember it very clearly. So I was around 12, 13 or something in an intro chemistry class at school, and we were doing electron orbitals. You learn about these s shells and p shells and so on. Particularly this p shell, it looks like a figure eight. And I was like, no way. Why is that, that shape? This is crazy. And I remember asking my chemistry teacher, why does this have this shape? And she said, “well, I mean there’s all sorts of answers I can give you, but nature just made it that way”. And I was extremely pissed by this answer. Perhaps a recurring theme we can get into is how I have been a bad student pissing off teachers and lectures and stuff like this.

(01:56): And anyway, other guests have said that they did not grow up in the internet generation, but I certainly did. So after the experience, I just went home and Wikipedia-ed the electron orbitals and the first thing you see is these funky words - ‘azimuthal quantum number’ or stuff like this. And I was like, “well, what is this word quantum and what is this ‘azimuthal’ word? “And so on, and Wikipedia has all these hyperlinks and you can just click from one to another and this sets me off on this phase of like, “oh, what is this and what is this?” And learning from one quantum concept to another. And as a result I just developed a deep curiosity about this wild scientific field…like, for me, it seemed like this frontier of unknown stuff. At least that still is very ongoing and active as a research area and I wanted to learn more about that. So after that I started to look into more stuff like that, read some books, like Feynman’s Pleasure of Finding Things Out was very influential on me, just like science aside, just someone who I felt lived their lives wanting to travel the world, get to know people and do science with these people. And I found that to be a very resonant sort of modus operandi of how to live life. And then later on in high school I was very lucky to meet a local researcher, André Xuereb, who I share the same surname with, but who is not related to me and who is sort of the first Maltese quantum physicist, you can put it that way.

(03:39): He’s an opto-mechanics guy and at the time he was still postdocing in Belfast, but he was switching between Belfast and Malta, starting a visiting professorship there. And we’d sort of meet once every two months to discuss quantum things. I had just bumped into him and told him about my interest and I think he appreciated that there was someone who cared about this stuff and started giving me books to read and stuff like that. And so I got a bit of this headstart into being interested in these types of ideas. Then later on in my undergrad whilst in Malta, there’s really not much in terms of course material that you can take related to quantum stuff. There’s only two, like a basic intro to quantum mechanics and then a quantum optics course in the fourth year, but there’s no quantum info. I was able to go to two of these so-called Squids summer schools organized by Lídia Del Rio and Nuriya Nurgalieva at ETH, both of which were very impactful on me firstly because it showed me that there’s a really large community of people that are looking to work on these very many different questions across quantum theory.

(04:54): And then I had went back the following year and there in particular Henrick Wilming - who I think actually postdoc-ed here in Berlin for some time - gave an intro lecture on quantum thermo and that really set me off. I was like, “this is some cool stuff”. I guess you hear the word demon in a physics context and you’re like, “what is this?” So more or less, yeah, that was the journey.

🟢 Steven Thomson (05:17): I think it’s quite striking that I guess some of the most influential things you mentioned there were…one was Wikipedia, which is, you know, open source community driven knowledge, and the other was these Squids schools, these summer schools aimed at getting people into the field. It’s nice to hear that those initiatives work.

🟣 Jake Xuereb (05:35): And especially coming from Malta. So something like Wikipedia is super important for a Maltese person. When I was 16, 17, I remember going to the main university buildings library for example, and trying to find books on quantum mechanics and you couldn’t even find one there. And so if there’s such little tangible resources, then the internet gives you access to anything. Then all of a sudden you’ve democratized the ability to start to learn these things, at least on your own. And then something like the Squids schools, I mean I can definitely say…they had these supporting bursaries, it gives you some money which enables you to be able to live in Zurich for four days. And I got one of those and that was super helpful. And like I said, if in Malta it was just me and this professor I could talk to and maybe some older Masters students that I could talk with.

(06:33): Then you go to Zurich and there’s 80 people and you meet people like, I dunno, Renato Renner, Scott Aaronson was there the first time I was there. And you see that it’s a worldwide community of many people. That stark difference sort of tells you, “hey, there’s more out there” and inspires you to make that leap. So I definitely do think that we all should do our part to create these types of inclusive opportunities to support people from diverse geographic backgrounds, even to join in this quantum fun that we all have. Whether that’s like if you get a paper to peer review with bad English from some country and you’re just a bit sensitive to that, you’re not going to dismiss it just because it has bad English, but maybe you help out or if there’s a master student looking to intern in your group, maybe you consider, “hey, they’re from this country which doesn’t have too much access to doing research in this topic. Maybe I should consider them.” I think that’s extremely important and something that a lot of PIs can do to make a difference.

🟢 Steven Thomson (07:39): You mentioned there Malta being I guess under-resourced in terms of science. Does this come from, is this historical factors? Is this current government priorities? Is there a reason?

🟣 Jake Xuereb (07:51): I mean these are of course complex questions, so I can only give my opinion, but I think of course there are historical factors. So Malta has only been its own country for 65 years. We were a British colony and colonized by other people before that. And as a result, let’s say you compare right now we’re sitting in Berlin or I work in Vienna. These are places that have been doing real physics and hardcore research for hundreds of years. And in doing so, you develop a research culture that has spanned those hundreds of years, you develop funding structures and so on. And so if we’ve only existed as a country even for 60 years, then that’s very different. I’d say we’ve only been doing physics as a country, as a people for 30 years properly. That’s why we only had our first quantum physicist 15 years ago.

(08:44): And that is a striking difference because I guess it’s just not clear for a Maltese person growing up that they could even aspire to do something like that. So that type of visibility or giving people access to these types of opportunities is very important. A larger or broader question is then how does scientific funding contribute to this problem presently? And is there things that can be done to change that? And I don’t know the answer here, but at least I can flag the problem, which is that if these countries like, I dunno, Germany, Austria, bigger central European countries and other countries like them, that have such a leg up on smaller countries, get the lion’s share of these major European grants.

(09:36): I can tell you statistics, for example, in a given year, Germany applies for 350 ERC grants (Starting Grants) and Malta since the start of the ERC has only applied for 33. So there’s an order of magnitude difference across the number of grants we’ve applied to since the beginning and that Germany applies for in one year. And we only got one ERC Starting Grant so far as a country. So I’m just like, these are just statistics. People can look them up. I’m not saying I know the solutions, but clearly there is an uphill battle for these countries that have only been doing science themselves for such a short time. And unless there are initiatives to support people from these countries, they are going to be isolated and marginalized scientifically. And I think science is one of these beautiful endeavours that we do as humans and we learn about these amazing ideas and somehow as scientists we have access to understanding these beautiful things the same way, I dunno, artists really understand a painting or something As a result, I think it is our duty to make sure that there is as much access to these beautiful ideas as possible.

(10:43): So we should all try to work on making that access very equal and equally distributed.

🟢 Steven Thomson (10:48): Yeah, yeah, definitely. And we’ll come back to your career in a moment, but that’s maybe a good point to mention that you’ve been involved in organizing a lot of summer schools and workshops and things in Malta, despite the fact that you’re a very early career stage. Is this the reason…?

🟣 Jake Xuereb (11:05): Completely, yes. So I feel like I’ve had extremely good luck as a Maltese person, like say going to these summer schools or André being young enough, - André my undergrad supervisor - being young enough at the time as a senior postdoc, not busy yet to give me that time or a number of such opportunities that allowed me to in a sense, or in my Masters, I was able to do half of it in Dublin with Steve Campbell and John Goold, and now I’m in Vienna. So I’ve had extremely good luck and I’m in such a good position now. I feel like a responsibility to try to foster more opportunities for people there. And the thing I can do is sort of bring people together, maybe get some money from a sponsor or something to create something like a summer school in Malta. Because if you bring PhD students and a couple of really cool visiting lecturers and maybe even some people from startups like we had at Qalypso a year ago, then this can be a very inspiring event for people.

(12:13): I can really tell you examples of this, there was this CS undergrad, 19 year old guy came over, he participated in our basics track and the hackathon where he placed second, he did another quantum hackathon after he had no quantum knowledge before this since then took quantum units in his undergrad course and this year he went to a summer school at the ICTQT and he’s totally into quantum cryptography now, and we’ve never had anyone from Malta into quantum cryptography. So if we can do more and more of that, it’s great because you’re giving people, like I said, from these diverse geographic backgrounds, more access to the type of fun that people like us have. And I think that’s super important.

🟢 Steven Thomson (12:59): I think there’s an interesting point in there, I think in terms of if you make these things accessible and you sort of get one person…so for example, you got into quantum and then you’re paying that forward, now you’re getting more people from malt and then hopefully that’s just going to grow exponentially. So all it really takes is that little bit of effort and the right person, right place, right time for sure. And then it can explode.

🟣 Jake Xuereb (13:23): Yeah, one hopes.

🟢 Steven Thomson (13:25): Nice. So you mentioned there you did your Masters half in Ireland. How did that come about? Why did you choose to go there?

🟣 Jake Xuereb (13:34): Yeah, so I mean being from Malta, somehow you have to be aware of the game of science a bit ahead of other people because it’s not like…I mean there’s no PhD funding in Malta, for example. So I mean, unless you decide to do a PhD not being paid, which I wouldn’t recommend to anyone–a PhD is a job and you should get paid for your job. You have to be aware of, okay, so there is a bit of a game here. I want to get employed. Employed maybe in a good group, but good groups probably hire already from other good groups. So there’s a bit of a game here. So even this, if you come from a smaller country, unless you have done some amazing stuff, I dunno, maybe you have extremely good grades and maybe the professor of your local university knows someone.

(14:17): And so it’s very hard. So I was maybe a bit too aware of this at the time. And basically after I finished my undergrad thesis, I decided, “look, I’m going to take this summer and instead of taking it off, I’m going to start working on some Masters research”. Because basically the people at the University of Malta were like, “okay, dude, you can do two things. Either you go do two years to do a master’s somewhere else in the EU…”, which can be very financially demanding, especially for someone who has to basically leave their country, which is an island, right? It’s not like you’re in central Europe, you can just take a train or something.

(14:58): Or they’re like, “…you can do a year here, you will have no taught classes, but we’ll let you do whatever you want, write up a thesis and we’ll give you a Masters in research.” And I was like, okay, well I feel like I’ve done decent enough in undergrad research. I actually liked the research more than sitting for classes, so maybe I should double down and see how this works. And so that summer I was able to get some really preliminary results analyzing the thermodynamics of a particular quantum algorithm. And basically I just started emailing people. So I emailed Steve Campbell, I emailed John Goold, then I emailed Nico Friis from the Vienna group actually, and they were all very kind to me and quite interested to hear about what I was doing. And I suggested, “Hey look, I have this research, it would be really, really cool if I could, would spend some time in your group just to learn from the people in your group”.

(15:51): Because in Malta I only had access to one or two people who are very busy because since our faculty is so small, the professors end up having to teach three, four courses a year. So they also don’t have so much time. And thankfully enough, John and Steve were both very interested and we were able to apply for a Malta Council for Science and Technology grant, which allowed me to go over there with some money. And also I got to a local scholarship in Malta, which helped during that time. And as a result I was able to spend some four or five months across Trinity College, Dublin and University College, Dublin learning from these two groups, which was tremendously impactful because like I said, I went from being around two quantum people I could talk to basically something like 25. And I can’t even put into words how just so much of a difference it made to me scientifically.

🟢 Steven Thomson (16:51): I think there’s, I guess a lesson in there for anyone about being proactive and not being afraid to reach out. Certainly it’s not something that I would’ve done at that stage of my career. I would’ve been just too afraid. I wouldn’t have known how to approach these people. I wouldn’t have even thought that that would be an option. I thought they would just, senior professors are probably not going to be at all interested. Why would they give me any time? And I never really considered doing that. But obviously it’s worked out for you, it’s worked out for other people. There’s definitely a lesson in there about being proactive, identifying what you want to do.

🟣 Jake Xuereb (17:22): And maybe emailing a PI is scary or you think they won’t reply, find a postdoc that does stuff which is similar enough to what you do and they will totally be interested in talking to you.

🟢 Steven Thomson (17:34): I think that’s something I’ve learned now after a few years in science, scientists do want to talk about their work. So if you show some interest in it, they’re probably going to take that opportunity to talk about it. Right. They’re not so likely to tell you to get lost for

🟣 Jake Xuereb (17:47): For Sure.

🟢 Steven Thomson (17:48): But yeah, it’s definitely an interesting lesson in there I think. So I normally ask people if they weren’t doing their current job, what else would they be doing? But it sounds like you’ve had a very single-minded focus on this for a very long time. Is there any other career that you’ve entertained along the way or is this just…?

🟣 Jake Xuereb (18:05): Yes, totally. So I’ve had a very singleminded focus, true. But I kind of for some time had this dual life a bit because for three years out of the four years I was an undergraduate student, I ran this educational tech startup in Malta called LearnD where we used to connect university students with younger students that they could tutor basically. And I mean, of course this is an idea which has been done elsewhere. It’s not particularly novel, but it was important in the educational context of Malta because there wasn’t so much one-on-one education going on. And I really enjoyed that. I enjoyed the prospect of solving a problem by working with other people and building something towards it. It’s a lot like science, it’s just the types of problems are different. And I enjoyed that a lot. I felt that it gave me a lot of confidence and communication skills in terms of, I dunno, raising money for a startup or something.

(19:03): If you can do that, then it’s easy to email a PI. So that definitely helped. And I entertained doing similar stuff like that. And ultimately what made the difference for me was, like, “what do I want my day-to-day life to look like for the next five years and what type of skills do I want out of it?” And for me, I wanted my day-to-day life to look like learning about quantum information, developing those skills, being able to answer quantum questions for the rest of my life, be that towards building some sort of startup or doing things in academia and building communities around research and academia. So that’s ultimately how I made that decision.

🟢 Steven Thomson (19:45): I think again, there’s another really interesting thing you said there, which is about identifying the skills that you want and then pursuing the path that gives you that. That’s something that I’ve advised people when they’ve asked me, should I do a postdoc? Should I do a PhD? What I usually say is, what skills do you actually want? Is it the dream of becoming a permanent professor or is it a case of, okay, I want to learn this particular thing. I want to maybe have the opportunity to go to this country to learn this technique, work on this field? I think if you know what you want out of a PhD or a postdoc or something like that, I think it’s much easier to be happier to actually enjoy what you’re doing because you’re always getting something from it.

🟣 Jake Xuereb (20:27): Yeah, for sure.

🟢 Steven Thomson (20:28): That’s maybe a good point then to talk a little bit about your research work. So we talked about your career and you’ve mentioned that you work on quantum thermodynamics. So what is quantum thermodynamics? That’s a big question, but for our audience who might not be familiar with this, can you break it down for us, give us a summary of what the big questions in quantum thermodynamics are and why is it interesting?

🟣 Jake Xuereb (20:50): Sure. So maybe we should start by outlining what thermodynamics itself is because it’s very broad. I often like to say it’s the operating system of physics and other ideas and physics are just apps on that operating system because thermodynamics is just the idea of understanding how energy is exchanged between systems and how it evolves and so on. And any physical theory needs some notion of energy, which is just I guess this sort of phase space invariant…I dunno how to say that in better English, but it’s some quantity which allows us to track the evolution of some dynamics. And thermodynamics then allows us to ask question about where the energy is going. Is it being dissipated in the form of heat? Is there some irreversibility in this dynamics which we can now relate to the increase of entropy, which is that irreversibility and this dissipation and is any external agent performing work on the system to increase these thermodynamic quantities?

(21:56): And so this whole field started around the 18th century with people trying to understand steam engines like Sadi Carnot and Fourier in the army of Napoleon and in the middle of the desert understanding cannons and stuff like this and then evolved. So it was first this phenomenological theory of people just looking out and saying, “ah, this should behave in this way.” But then people like Boltzmann came along and thought about how, okay, if these gases are formed by particles, we should still be able to recover these ideas from these particles and came up with a nicer theory of statistical mechanics, which is still thermodynamics. And so thermodynamics really is about seeing how the constituents of a system exchange informa…ah, exchange energy, I’m already preempting myself. And so now in the modern era, there’s people like yourself who want to understand the thermodynamics of these condensed matter situations like these spin glasses or so on, these chains of electron spins and so on.

(23:01): But in quantum thermodynamics, there’s so many different aspects, we want to understand the exchanges of heat and of entropy in the context of these lonely physical systems like atoms, clouds of atoms, and in particular quantum thermodynamics around 2016, 2017 took a very information theoretic spin to it. So entropy is definitely even in the normal context of bits related to the information content of some object. Of course, it’s also related to the irreversibility of a process, let’s say a gas undergoes, but you can also talk about the information which that gas encodes. So if a gas is at a particular pressure and temperature, so it’s at a particular energy, you can ask in how many different configurations can that gas be in such that it still has this energy– and that’s information. So there is a deep relationship between information and entropy and thermodynamics, even classically. But now it gets even more interesting because now the correlations, this information content is more complex. We have things like entanglement, which is now a different type of correlation, which is more complex and really about the structure of how the mathematics of quantum objects works and this separability of these quantum objects, which then makes the thermodynamic questions even richer. So if even classically there was this relationship between information and thermodynamics, now we want to understand the relationship between quantum information and thermodynamics. So I would say that’s really what the field is trying to do.

🟢 Steven Thomson (24:43): So it’s like classically you have this correspondence between the number of configurations of a system and energy, but then as you say, when you turn on quantum mechanics, now you have this whole extra dimension of entanglement and quantum information on top of that which gives you, I guess a richer playground to work with.

🟣 Jake Xuereb (24:59): Indeed. So people have done many various kinds of things in this regime. For example, looking at these so-called quantum thermal machines, which one can form out of these very small two-level systems, right, qubits. So these quantum objects which can exist in two energy states, you can think of for example, an ion. So you take an atom, you knock off the last electron, now it’s an ion. And there is this state of this electron, which can be either in an excited state before it almost leaves the atom electromagnetic region completely, or it can be in the ground state where it’s fairly localized within this atom. So you can think of two level systems in this way, and now you can ask, “oh, if I bring a couple of these two level systems or we can call them qubits together and now we do things to them, we hit them with a laser and particular energy and so on, what types of thermodynamic interactions can we see?”

(25:55): So maybe these atoms bunch up, maybe they dissipate heat to some environment, maybe they get heat from some environment, and people have looked at forming engines out of these types of situations. People have looked at how measurement – quantum measurement, right, this external system interacting with our quantum system, leaking information into it – also has a thermodynamic character to it. And just a whole plethora of questions. If you have a quantum system, why would it equilibrate, right, like tend to some finite temperature? What’s the relationship between entanglement and thermodynamics more generally? Can you make statements about this stuff? What’s the thermodynamic work that goes into forming entanglement? And what dissipation do you get out of destroying entanglement? These are all open questions which are still somehow unanswered. Can you use thermodynamics to quantify entanglement? There’s all these fun questions that one can start to attack there.

🟢 Steven Thomson (26:58): So is there a sort of a big picture goal of the field? Because these are all very fundamental physics questions. Is quantum thermodynamics a field that’s interested in fundamental questions only or is there any kind of application to any more quantum technologies or anything like that?

🟣 Jake Xuereb (27:17): For sure. So there are people that really work on the foundations of quantum thermodynamics trying to understand something like measurement for example, from a thermodynamic lens because measurement takes you from a state which is in a superposition between two quantum states to one which is well-defined, something which is like a thermodynamic impossibility. And if you’re working in quantum thermo, it then sort of behoves you to try to solve this. So there are people in our group in Vienna trying to solve precisely this question for these quantum systems, if they’re so funny, how do they tend to equilibrium for example? That’s another foundational question. The relationship between entanglement and thermodynamics is a foundational question, but as you point towards quantum technologies themselves are also thermodynamic objects and we should understand their quantum thermodynamics. And this is maybe a good place for me to mention what I’m motivated by in my research.

(28:13): So things I care about are maybe let’s say twofold. Like, if you have a quantum computer, right? So a quantum computer, one of the very important things is that each quantum object, each qubit in this computer is isolated and addressable as its own isolated thing. But you want to also do operations between these qubits, we can call them gates, which lead them to interact, but without spoiling this isolation between each time step, and this is kind of a thermodynamic problem, so you want these things to interact without interacting so much that they kind of spoil their isolation. So people come up with things like error correcting codes, for example, to preserve that isolation, thinking about it as an information problem. But surely you can think about it as a thermodynamic one as well. So if I have some error in some specific region of my qubits now if I bring some more in and I do this maybe global operation now that I’ve brought more in now can push the error or the entropy down to these other qubits I brought in.

(29:12): So you can think about error correction in a thermodynamic way. You can also think about the resources behind a computation. So if I do something like a gate on a qubit, and I mentioned earlier that we can think about this as a laser hitting a trapped ion, then I’m running this laser for a period of time, for example. So there’s some notion of a clock there and a clock has some thermodynamic resources behind it. I’m expending some thermodynamic quantities to be able to track time. So how much resources do I need to do a computation? What thermodynamic resources go into doing a particular computation? And the question I care about quite deeply is if something is hard in a computational sense, so it has high computational complexity, is it true that it requires more thermodynamic work to do? I think that would be really cool to be able to show this type of relationship that if something is hard in an information processing sense, it’s also thermodynamically hard. Kind of like if you have a car and you want to drive a long distance, you need to burn a lot of fuel. It’s not necessarily clear that computationally complex things are also thermodynamically hard. And this is I would say the main goal or the main idea, which drives what I like to do.

🟢 Steven Thomson (30:29): That’s really interesting. I think there are a couple of points in there that I really like. I think one is the fact that you mentioned gates as being a microscopic process of lasers and ions. The abstract picture of gates has always really annoyed me. So it’s always nice to hear when people talk about them as being physical processes. But yeah, this link between complexity and thermodynamic work is interesting. And on one hand it feels like it should be true, but I guess then when you start using words like complexity, there’s so many different definitions of complexity. And then as you mentioned, the difference between quantum information, classical information, classical thermodynamics, quantum thermodynamics, I can see that question probably becomes quite hard to answer once you enter the quantum realm.

🟣 Jake Xuereb (31:10): Indeed, it’s currently, I would say, very hard to even pin down a notion of complexity that works in the quantum thermodynamic sense. So of course in the context of quantum computational complexity, you can think about resource complexity, how many gates are you running? And maybe you care only about entangling gates because they cost more. And so that’s a very good measure of complexity in that context. But if I care about just general quantum operations, so things people might call channels like this way of going from one Hilbert space to another and to just thinking about these mathematical objects, how do you talk about the complexity of a channel? This is a very open question and one which is not clear and one which we’re trying to address. Is there even a good universal notion of complexity in a quantum context? It seems like it’s very context dependent as well. The notion of complexity

🟢 Steven Thomson (32:04): In terms of different physical setups or…?

🟣 Jake Xuereb (32:08): In terms of the task you’re interested in. Oh, so there is this work that came out of the group in Vienna led by Philip Taranto who’s now at the University of Tokyo. A project in his PhD was showing that cooling a quantum system comes at a cost of three different resources, which is the size of the, let’s say ancillary system you bring in to do a cooling protocol. So like the dimension of a quantum system, the complexity of its energetic structure of this system you bring in and also the amount of time you allow yourself to try to perform the cooling protocol. So in this context you could see that these are the three resources you care about. And so you can talk about complexity in that way, but if you really abstract away to come up with some general notion, you start to get lost.

🟢 Steven Thomson (32:59): I’m fascinated by what you’ve just said and I want to ask so many technical questions that are probably not appropriate for the podcast…

🟣 Jake Xuereb (33:05): Maybe one thing I should mention is that quantum thermodynamics right now is kind of very splintered or not splintered, but you can really think about it as there are these kind of different countries that do things differently. You can even think of a map of quantum thermodynamics where there are people from stochastic thermodynamics, people that care about more classical quantities about when does this quantum quantity fluctuate like entropy, when is it going up or down? What type of measurements can I do to measure this quantity? And they care about things like fluctuation dissipation, relationships. If I’m dissipating so much heat, how much fluctuations can I see in a given quantity? So it’s like one tribe of thermodynamics. Then there’s the resource theoretic people that care about these very abstract mathematical objects that tell you if I want to go from quantum state A to quantum state B, what’s the thermodynamic relationship between going from A to B?

(33:54): And you can come up with all these nice funky mathematical quantifiers like Rényi entropy and so on, but this is completely different from these stochastic people. And then I would say you have these more operational thermodynamics people, which I would say is sort of what our group do. For example, you take cooling and you say, okay, how many swap operations am I going to do to cool this object down? So these are people who are saying, okay, I can pin down these operations and I can think about the thermodynamics of these operations. And there are even more tribes. You can talk about the condensed matter people that do quantum thermodynamics and talk about equilibration, the eigenstate thermalisation hypothesis, this big, big term about why do quantum systems equilibriate and all these people are trying to get at the same questions from different angles and somehow this is the beauty of the field, but it’s also the challenge the community faces to try to unify together and say, “listen, we care about these questions, how are we going to attack them?” And that’s something which I think all of us in the field should think about.

🟢 Steven Thomson (34:54): I guess even perhaps communicating between these different communities must be a challenge if you’re using different words, different techniques.

🟣 Jake Xuereb (35:00): Indeed.

🟢 Steven Thomson (35:01): Different goals.

🟣 Jake Xuereb (35:02): And this really starts to draw into the sociological aspect of science that like science is a human endeavour and if you just choose to bury your head in the sand and say, “I like these techniques and I’m going to answer these questions”, and you never look to your left or your right, your colleague might be doing the same exact thing and you’d be completely missing that. And so I think we should all try to, I mean this is another point which maybe brings back to the start of our conversation like summer schools and these social aspects of science are important not just to bring people into science, but for ourselves as scientists to do science well together because I think we only do science well together if we also have fun together as a community and enjoy collaborating and not feeding into this whole competitiveness of the game of science.

🟢 Steven Thomson (35:54): Maybe that’s maybe a good point to ask actually…as one of the earliest career researchers that we’ve spoken to, you’ve transitioned from the undergrad education to research relatively recently. How have you found that transition? Did you find that you had to have a completely different mindset to begin doing research? I think a lot of people who are in the research field probably don’t remember that kind of mental shift that they have to go through?

🟣 Jake Xuereb (36:20): So I always like to say that there is some sort of probability distribution of suffering and time which is normalized. So it has measure one and where it’s peaked is different for everyone, but you’re going to experience some amount of suffering when you start doing research because I mean basically it’s like being thrown at the deep end of a pool and you don’t know how to swim yet, especially in these big fields now in science and quantum theory in general is so vast. If you bring a master’s student that did even a quantum info like a graduate course, and now you’re telling them, okay, let’s do this project on quantum error correction or quantum thermodynamics, there’s just so much literature that they have to deal with. And I think in these situations you just have to remember, hey, everyone around you started in that situation and they knew nothing and it’s completely fine to know nothing and take your time with it.

(37:15): In some sense, we have the deep privilege of hanging out with these very nice ideas and we should treat it like that. We shouldn’t feel this like, “oh, I have to learn this so quick so I can get this project done, get this paper out”. So for me, I was always thinking about this. I’m just trying to enjoy these ideas, learn about these ideas. If I can learn about these ideas from the people around me, that’s even better. So that was my main motivation to go to Ireland, was to hang out with these quantum thermo people, learn quantum thermo from them, socialize with them. And that aspect definitely gets true through these periods which just suck and nothing works out because if you can at least have fun once you’re doing that, then that’s great. And yeah, I think so many people I’ve seen this in, people around me sort of really feel like they can’t admit that they don’t know something because I think coming up in these hard natural sciences, most of us are quite competitive and we like to seem bulletproof or whatever, maybe because we grew up with that idea of a scientist, but the moment you realize that everyone is quite dumb and a goofball and knows nothing, they just have been doing it for so long and they have very specialized knowledge now, then you understand that, “hey, it’s okay to be you, to take it at your own pace and just have fun, socialize with the people around you, enjoy these ideas.”

(38:36): And then eventually you’ll get a nice idea, maybe you start to work on it, it’ll also suck because you’ll get stuck. But then magically, somehow you’ll be at the desk one day and randomly the solution will appear on its own and then it starts to move. So I think just understanding that everyone has it hard and understanding that that’s a part of the process and learning to have fun with it is just the key to making that transition between being an undergraduate student that studies for exams and a researcher that does that research.

🟢 Steven Thomson (39:06): Yeah, I think I agree. I think there’s almost an element of just accepting and embracing ignorance when you go from answering questions that have well-defined answers and then you start doing research where even the questions are maybe not well-defined, and it is okay to admit that you don’t know everything about everything. And although these highly specialized topics…no one’s expected to know everything, right?

🟣 Jake Xuereb (39:28): Indeed. I mean also when you get into research, maybe initially you’re quite scared of this, but then you start to work with very good people and they say stupid things in front of you and you’re like, oh, okay. Everyone is fallible. Even these big shot scientists are all making mistakes all the time. They’re just okay with it and they can walk through it. They don’t just freeze up. And once you accept that everyone says stupid things a couple of times a day, then you feel fine.

🟢 Steven Thomson (39:57): Yeah, absolutely. Well, talking of the people in science, I think that brings us nicely onto one of the questions that I like to ask everyone on this podcast, which is that physics in particular has for a very long time been a field dominated mostly by white cisgender men. It feels like things are perhaps changing albeit very slowly, and there’s still a long way to go. You’re still very early in your career, but having worked in a couple of different countries, well, having worked in a couple of different countries, how does the issue of diversity in physics look to you? And I guess B, as someone early in your career looking at researchers who have been doing this for decades and all these different research groups, do you think that things are changing? Does the future look hopeful or does it look like we’re stuck in a bad situation and not doing enough to get out?

🟣 Jake Xuereb (40:48): So I would be very hopeful because, even let’s say across the four or five years that I’ve been going to quantum events and stuff, I have seen a discernible change. Is this true across the board within a research group, for example? Because if you’re in a conference, you’re at the conference, it’s a large enough sample size that maybe even small effects start to make themselves known. So if there are more diverse people in a small percentage, a large sample size, you will start to see it. But if you go to a given group, I would be comfortable probably estimating that three out of every five or two out of every five theoretical physics research groups are still all men or all men and one female for example, or one diverse person. And the groups where this is not true, where it’s like they hire PhD students, 50:50 for example, are PIs that are legitimately taking it upon themselves to make that difference.

(41:49): And I think the way forward is people just doubling down on that and more people taking that inspiration from these groups and saying, “Hey, I want to make the environment of my research group more comfortable for more different kinds of people and I’m going to achieve that by hiring more diversely.” Aside from that, I think if we continue to have events within conferences within summer schools, which support people from diverse backgrounds. So I really like it when at the conference or at the summer school, there are these small sub events for people from diverse backgrounds to talk about their experiences and feel supported and not alone. I love to see that and I hope more of it happens. And whilst I think as I’m saying, it is quite optimistic, we can’t sleep on this. And also maybe as I spoke about earlier in this conversation, we need to treat also different types of diversity. So even geographic diversity and things like that are things we have to consider both in the language barrier aspects to people doing science because science is mostly done in English, but not everyone learns English equally well. And also that it is harder for people from different geographic backgrounds to break into science. So we should all keep those things in mind.

🟢 Steven Thomson (43:11): Yeah, definitely. I think they’re all very good points. Okay. One final question to wrap up with then. If you could go back in time and give yourself just one piece of advice, what would it be?

🟣 Jake Xuereb (43:24): I don’t know if it would be advice, but I was a very bad student. After the second year of my undergrad, I just basically stopped going to lectures and just started reading books. And so in Malta we had to do a double degree of maths and physics. We couldn’t just do physics, and I did well in the physics, but atrociously bad in some of the maths, like these Proofy exams with 30 proofs where you have to do it all by heart. So it was very demoralizing for me. Clearly I cared a lot about the subject. I liked maths even. I mean, I do quantum info today. I spent most of my days doing inequalities, so I cared about this, but it was quite demoralizing seeing these bad grades. And the only piece of advice I would give myself is like, “Hey, look man, not everyone that ends up being a researcher has to have a first class honors in their undergrad and has such a sterling academic record. If you just double down on what you’re doing and you sort of do what you’re authentically good at, maybe it’ll work out.” If I could just give myself that kind of hug, that’s the only thing I do. Because it’s what happened ultimately.

🟢 Steven Thomson (44:30): Yeah, I think it’s funny how many people, their advice to their younger selves is usually something along the lines of relax, don’t stress so much. That thing that’s worrying you a lot now in five years time probably is not going to be such a big deal. Yeah. Okay, cool. I think that is a very good note to end on. So if our audience would like to learn a bit more about you, is there any way they can find you on the internet or on social media?

🟣 Jake Xuereb (44:56): Yeah, I am reasonably active on Twitter at @curlyqubit. You can find out more about me at my personal website jakexuereb.com, and please always feel free to DM me or email me if there’s anything you think would be interesting to talk about or anything that you’re interested in that you think I can help with.

🟢 Steven Thomson (45:17): Alright, fantastic. We’ll be sure to leave links to those on our own website insidequantum.org. Thank you very much, Jake Xuereb for your time here today.

(45:26): Thank you also to the Unitary Fund for supporting this podcast. If you’ve enjoyed today’s episode, please consider liking, sharing and subscribing wherever you like to listen to your podcasts. It really helps us to get our guest stories out to as wide an audience as possible. I hope you’ll join us again for our next episode. And until then, this has been insideQuantum. I’ve been Dr. Steven Thomson, and thank you very much for listening. Goodbye.