Hybrid Quantum Materials with Charlotte Bøttcher
Welcome back to the New Quantum Era, the podcast that brings you conversations with the researchers, thinkers, and pioneers at the cutting edge of quantum science and technology. I'm your host, Sebastian Hassinger. Today, I'm excited to introduce a special guest, Doctor. Charlotte Bøttcher , who is launching her very own research group at Stanford University. She earned her PhD at Harvard and then did a postdoc with Michel Devoret at Yale and is now an assistant professor at Stanford and is setting up her own experimental group there.
Sebastian Hassinger:We recorded this at APS Global Summit with help from the American Physical Society, so my thanks to them. I'm almost done, the recordings that I made at APS Global Summit. There's only one left to go, and I've been recording some additional newer episodes. So you can expect to shift from APS conversations to newer conversations in the next couple of weeks. Doctor.
Sebastian Hassinger:Bøttcher is an experimentalist, as I mentioned, and we'll be talking about her work in hybrid material systems. She's a condensed matter physicist, so she's looking at superconducting devices and hybrid materials that combine superconducting materials with semiconductors. And these have some potential for tunable superconductivity, switchable quantum devices where you can turn on and off the superconductivity, and also search for exotic states of matter like unconventional and topological superconductors. So we'll hear about Charlotte's experiences building a new lab from the ground up, the interplay of experiment and theory, and her vision for both foundational science and real world quantum technologies. So I hope you enjoy.
Sebastian Hassinger:Hey, Charlotte. Thank you very much for joining me.
Charlotte Bøttcher:Thank you, Sebastian. Yeah. I'm happy to be here.
Sebastian Hassinger:How's your week been going? How are you enjoying the APS summit?
Charlotte Bøttcher:Good. Very busy.
Sebastian Hassinger:Yes.
Charlotte Bøttcher:Very exciting.
Sebastian Hassinger:Yes.
Charlotte Bøttcher:Yeah. A lot of very interesting and exciting, results and presentations.
Sebastian Hassinger:And you were presenting yourself as well. Right?
Charlotte Bøttcher:I did. Yeah. Yeah. It was in, earlier this week. And Okay.
Charlotte Bøttcher:Yeah.
Sebastian Hassinger:What was your session about?
Charlotte Bøttcher:So this was about hybrid material system that combines superconducting systems with semiconductors. Right. And so, yeah, a lot of really interesting research is going on both in quantum information technology, but also just fundamental physics questions that we can answer. Yeah.
Sebastian Hassinger:Right. And what were what are the what's the exact semiconductor and superconducting materials you're working with?
Charlotte Bøttcher:Yeah. So this is, in particular, aluminum. So this is a very standard Yeah. Superconductor that we understand and love. And then
Sebastian Hassinger:Who doesn't love aluminum?
Charlotte Bøttcher:I know. Right? Yeah. Actually, my mom works with aluminum too. Oh, really?
Sebastian Hassinger:Yeah. So it runs in your family?
Charlotte Bøttcher:It does.
Sebastian Hassinger:It does. That's nice.
Charlotte Bøttcher:Yeah. So yeah. And then we combine it with indium arsenide. Okay. So that's a little more exotic.
Charlotte Bøttcher:Yeah. Not a lot of people like to touch it. Right. So yeah. But it it creates a very exciting system to work with.
Sebastian Hassinger:Yeah. So, I mean, that's it's interesting. I I caught that a a while ago when I started hearing about these hybrid systems. It's it's literally two materials sandwiched together or or actually fabricated in some kind of very tightly integrated way that makes a, physical system essentially. Right?
Charlotte Bøttcher:Yeah. Yeah. And it really combines two two key elements that we love, especially from my perspective if I wanted to create something, you know, switchable devices. Mhmm. You know, this is for technology and and whatever you can imagine that, you know, for instance, your your phones, you know, you need switching for your transistors.
Sebastian Hassinger:Right.
Charlotte Bøttcher:And now in in quantum, you want something that is is is quantum technology and often also tunable and switchable. And because a semiconductor, which again is implemented in a lot of devices, gives you that switchability, but then superconductivity is sort of a very unique property that you can add onto it. Right. But now combining those two, it actually means that now you can also switch superconductivity on and off.
Sebastian Hassinger:So for example, I mean, I I remember the first time I heard this, the use case was two qubits where neighboring qubits are linked together so you can entangle them and do two qubit gates. Mhmm. But you could also turn off that link
Charlotte Bøttcher:Yes.
Sebastian Hassinger:And isolate each from the other and and reduce crosstalk and and noise overall in the system. That that's sort of the the quantum application, I guess.
Charlotte Bøttcher:Yes. Yes. And and superconductivity is also used to just make the qubit itself. And so it's used in in in various both academic groups to make qubits were not so scalable yet as the companies. Right.
Charlotte Bøttcher:But yes. So both in terms of couplers between qubits, but also the qubits themselves Right. Can be superconducting circuits, actually. Yeah.
Sebastian Hassinger:Yeah. And in terms of sort of foundational, scientific investigation, what what can you learn from from that type of complex system?
Charlotte Bøttcher:A lot. We can we can, dive into almost anything. Especially these systems, if you combine this particular superconductor and semiconductor, that can give rise to some more unconventional superconductivity. So that's sort of typically how we physicists talk about superconductors. You know, there's the vanilla kind, which is the aluminum.
Charlotte Bøttcher:We know it. Right. We can understand it very well and write down all of its equations.
Sebastian Hassinger:Right.
Charlotte Bøttcher:But then the unconventional ones are interesting for more exotic, states of matter. Mhmm. They're more fundamental questions that we're still learning about. Right. Topological superconductors.
Charlotte Bøttcher:I I
Sebastian Hassinger:had a feeling that word was gonna
Charlotte Bøttcher:come up. Yes. It's
Sebastian Hassinger:kind of one of the themes of APS this week, isn't it?
Charlotte Bøttcher:But I think that there's just still a lot to to even just understand about how can we control this superconducting phase even when we when it's very boring Right. As you would say.
Sebastian Hassinger:But Right.
Charlotte Bøttcher:Really it is
Sebastian Hassinger:Are there other exotic types of superconducting beyond topological? It seems like that's the it's hogging all the attention. So are there lesser known?
Charlotte Bøttcher:I mean, there's there's a whole range of sort of unconventional superconductors. There's actually what, people call high TC superconductors.
Sebastian Hassinger:Right.
Charlotte Bøttcher:So, I mean, recently, you also might have heard about, you know, room temperature Right. Superconductivity.
Sebastian Hassinger:Of course.
Charlotte Bøttcher:I mean, we're
Sebastian Hassinger:not Every couple years.
Charlotte Bøttcher:Yes. Every couple years, it comes up. But, you know, high high TC superconductors is sort of another category. Okay. And they are also unconventional.
Sebastian Hassinger:Okay.
Charlotte Bøttcher:And so and this is sort of very detailed in how exactly so in in superconductors, electrons pair up. And
Sebastian Hassinger:it Cooper pairs.
Charlotte Bøttcher:Cooper pairs. Right. Exactly. And the way that they pair up sort of according to the spin orientation determines whether they're the conventional kind or unconventional But in high TC superconductors it often turns into these unconventional pairing. And they're very complex and hard to understand.
Charlotte Bøttcher:But their critical temperature, the TC, is hundreds of Kelvin, which sort of, compared to something like aluminum, is 100 times higher. So it really is a fascinating direction to understand exactly how these interactions between electrons and how they pair leads to that regime where you get such a high critical temperature. Is
Sebastian Hassinger:it more disordered, the behavior, because of that complexity?
Charlotte Bøttcher:It's also it's often very disordered systems. Yeah.
Sebastian Hassinger:So harder to control in in a in an application like a qubit, for example. Yes. Yes. Interesting.
Charlotte Bøttcher:Yes. It is.
Sebastian Hassinger:But I suppose if you could understand well enough how the disorder is structured, might be able to still harness it for more, you know, whatever, useful applications that wouldn't need millikelvin kind of range. Yes. Interesting. That's really interesting.
Charlotte Bøttcher:Yeah. I I would say that in particular quantum simulation is something that Right. We are sort of starting to realize is actually quite powerful to predict some of these, you know, more complex systems. And I think that's also something that we're doing in in in my group, is to to try to understand what really gives rise to these strongly correlated systems.
Sebastian Hassinger:Right. Right. You mentioned your group that's you've just established your group for the first time at Stanford. Congratulations.
Charlotte Bøttcher:Thank you.
Sebastian Hassinger:What has that been like to sort of transitioning from so, for context, you were a postdoc with Michelle Devore at Yale. Devore is very, very well known and has had a long career with many incredible accomplishments, you're now sort of launched out into your own professorship and you're and starting to build your own group. What's that been like?
Charlotte Bøttcher:Yeah. It's been exciting and a lot of work, but I think it's it's just every single day you're enjoying it, I think. It's exciting to work with young students and and the new generation to, you know, teach and work with them. And, you know, we we're starting to get our new first systems. So Right.
Charlotte Bøttcher:We work with these dilution refrigerators where we can cool down, let's say, superconductors and these materials. And we have to install everything from the beginning, and that's that's a lot of fun.
Sebastian Hassinger:Yeah. You like building a lab?
Charlotte Bøttcher:Oh, yeah. Yeah. Yeah.
Sebastian Hassinger:I think that's it would be really tough to be an experimental physicist and not love building labs. Right?
Charlotte Bøttcher:Right. Oh, yeah. Yeah. For sure.
Sebastian Hassinger:So what do you do you have a sense of what your agenda, what your goals are gonna be for the group initially?
Charlotte Bøttcher:Yeah. I, I think that we're sort of a hybrid group, like the materials a little bit. We we would like to build devices that can be applied to, let's say, in the quantum information direction. We're focusing on on more on new systems, new materials that can be applied to add new functionalities to those qubits. Also, we're just interested in understanding very complex systems.
Charlotte Bøttcher:So that's where quantum simulation comes in and also quantum sensing. And I think quantum sensing is something that, know, actually qubits and these quantum circuits, one of the sort of the bottlenecks for using them is the fact that they're so sensitive to their environments. But that can be very useful if you want to send something with them. So one thing we're doing is also just applying some of these technologies to probe and sense systems that we don't know much about. Mhmm.
Sebastian Hassinger:Yeah. So other quantum systems then? Interesting. What would be an example of of I mean, you're sensing a magnetic field or what what are the characteristics you're trying to sense?
Charlotte Bøttcher:Yeah, it could be magnetic degrees of freedom, charge, yeah, superconducting properties, interesting insulating properties, coexisting degrees of freedom. Really, you know, as just an example, we're using a really interesting crystal that's comprised of uranium, but is actually a superconductor. And that's puzzling and people are just trying to understand, you know, what exactly is the the nature of this superconducting Right. State and so
Sebastian Hassinger:that's much heavier element than Oh, superconductors are, I think. Right? Yes.
Charlotte Bøttcher:Yes.
Sebastian Hassinger:Interesting.
Charlotte Bøttcher:It has a very complex phase diagram and and so and here we can couple to something that's called collective modes. Mhmm. So they're collective excitations of the spins in the superconductor. And that gives us a way to couple because the spin is slightly magnetic moment. And so we can couple these quantum devices or qubits to that moment and and actually put quite strongly potentially.
Charlotte Bøttcher:So that will give give us a way to couple to these systems that we're not really that we don't know much about yet.
Sebastian Hassinger:Interesting. And when you say quantum simulation, are you building devices that that simulate a Hamiltonian, that essentially run a Hamiltonian or or whatever. Can observe the time observe time evolution of that Hamiltonian?
Charlotte Bøttcher:Yeah. That's that's kind of the idea. Yeah. Yeah. So we're looking at different kinds of Hamiltonians.
Charlotte Bøttcher:And you can think of a very simple one, or at least to us it's reasonably simple. But the key is really that it's a man body system that we're trying to simulate. So it's many particles that interact. And then the question is also, what kind of particles? And here we're looking at both bosonic particles and then there's also another category which are fermionic.
Charlotte Bøttcher:Right. And they can all give rise to very different kinds of Hamiltonians, but that we think that we can we can potentially synthesize in our systems and actually control. And then going back to sort of earlier, like disorder and complexity, we also have a way that we could potentially control disorder and actually turn that on and off and see how that interacts with with our Interesting. Phonon.
Sebastian Hassinger:Yeah. How do you control disorder? Yeah. Seems like a contradiction term.
Charlotte Bøttcher:It's it's it's a little bit yeah. It it sort of comes again back to to the materials and how materials can be affected by different parameters. And so one way that we can control a semiconductor is by electric fields.
Sebastian Hassinger:Right.
Charlotte Bøttcher:And these electric fields can tune your sort of density of carriers. And often when you have a lot of carriers around, they actually together help screen if there are any defects in your system.
Sebastian Hassinger:Oh, interesting.
Charlotte Bøttcher:So the more you have, the the the less you really sort of average over all these defects. But if you decrease that density, each of your electrons now, see more clearly the defects of the disorder that's in the system. And so just by tuning, let's say, your density of carriers, you can effectively also
Sebastian Hassinger:And carriers, you mean electrons on the surface?
Charlotte Bøttcher:Yes. Okay. Yeah. Okay. And so that's a way to at least tune your susceptibility to disorder.
Sebastian Hassinger:I see.
Charlotte Bøttcher:Yeah.
Sebastian Hassinger:I see. So the disorder is is inherent to the underlying Yes. Material. Yes. And the the density of electrons either exposes or Yes.
Sebastian Hassinger:That's really cool. Yeah. That's really, really cool. So, I mean, I I I can kind of guess the answer to this, but what's the advantage in your mind of of, you know, building a simulation device versus trying to simulate in a quantum computer? Is it I mean, if that's a if you have a universal quantum computer, then theoretically, you should be able to create that simulation in the computer as well.
Charlotte Bøttcher:Absolutely. Yeah. I think there's there's certain advantages right now, which is that we can make more sites or or more particles Right. Interact because of the systems that we're using. So we can get up to thousands of particles that can interact with.
Sebastian Hassinger:Beyond way beyond the scale of current computers.
Charlotte Bøttcher:Right. And so but at some point, I do think that, you know, they will overcome and it will be a lot more advantageous to use a quantum computer. And we're not there yet, so we're kind of, you know, in this between, you know, use and application
Sebastian Hassinger:Right.
Charlotte Bøttcher:And and, yeah, research, I would say. Yeah.
Sebastian Hassinger:It's interesting. I've I've heard of I'm although I've never actually heard of how we actually building, but I've heard the idea of floated of of sort of hybrid, you know, purpose built simulation with some degree of of universal gate based qubits as well. So you can sort of combine maybe control or sensing of that simulation device or from the from the computation. Is that something that that you would think about doing? Or is that
Charlotte Bøttcher:Yeah. Yeah. So I think that we're definitely looking into more sort of local control also, and how we can, let's say, have one local site interact with another, and how does that work for this collective system. I also know that that can be hard in certain systems where, for instance, atom arrays are another way that you could also have control over particles. And actually superconducting qubits is another direction where you can use the sort of the state, either the zero or one state of the qubit as sort of a particle as well that can interact.
Charlotte Bøttcher:And here, yes, single qubit gates become important. We're not sort of there yet in terms of our quantum simulator or the direction that we're working in, but this becomes an important question too.
Sebastian Hassinger:That's really cool. And your experience as a as a postdoc, I mean, Yale is sort of, you know, the the the storied Valhalla of superconducting qubits. You've got transmods and bosonic qubits and, like, so many dual rail qubits now all coming out of the Yes. The Yale gang. What was that like being been part of that that sort of organization in Deborah's group?
Charlotte Bøttcher:It was a great experience Yeah. For me. It was definitely a very unique place. I think that there is a great interaction between experiments and theory that I don't really think I've seen other places where I've been. And so you just kind of run into theorists and and you can talk to them.
Charlotte Bøttcher:I'm an experimentalist, so run into theorists, you can talk to them very easily. Rob Shulcove is there as well on the same floor, and so the interaction between the two groups is really valuable. And I think that for me, was the best place that I could, you know, dive into these superconducting qubits and and learn a lot from from the experts in the field Right. I would say.
Sebastian Hassinger:Right. And are you continuing collaborations between your group and and the Yale groups?
Charlotte Bøttcher:Yes. We're still yeah. So actually, I so Michelle is now moving closer to Google.
Sebastian Hassinger:That's right. Yeah. That's right.
Charlotte Bøttcher:In fact, yeah. And but that means that that's on on the West Coast. Yeah. And so our groups could potentially more easily interact as well. But we do have some grants together that we're continuing.
Charlotte Bøttcher:And also another professor actually at Yale that we started interacting with on sort of the material side, we're also still collaborating Yeah.
Sebastian Hassinger:That's really good. And so, like, when you think about, you know, next APS, what what work do you hope your group will be presenting? Obviously, I don't wanna give away any secrets so you don't get scooped or whatever. Yeah. But but, yeah, do you have a sense of what what you wanna accomplish in the next year?
Charlotte Bøttcher:Yeah. I I think, first of all, you know, just having working systems. Yeah. That's goal number one. But, yeah.
Charlotte Bøttcher:Just picking up a little bit what we where we left off at Yale. So we're building news these new kinds of superconducting qubits that can work at higher temperature and higher frequency, which is now also what is is sort of actively explored in the field to build more scalable systems.
Sebastian Hassinger:Right.
Charlotte Bøttcher:So I'm hoping that we're gonna have at least a couple of working qubits by next year that we can present on, and hopefully, the coherence times are are good as well. And then maybe we'll have some initial results on the quantum simulation platforms. Right.
Sebastian Hassinger:So yeah. And the hybrid systems, is that something you're gonna continue in the new group as well?
Charlotte Bøttcher:Yes. Yes. We will. And in fact, yeah, our collaborator that we're growing these hybrid systems, we've we've been talking to and and, yeah, about getting these samples.
Sebastian Hassinger:And when you when you think about topological systems is are you are you hunting for the Majorana Fermion as well?
Charlotte Bøttcher:I would say if if they show up in a in our systems
Sebastian Hassinger:They're
Charlotte Bøttcher:welcome. They're welcome, we wouldn't mind. But, yeah, I think for now, there's a lot of other exciting directions. And I think that we're we're probably working close in the same regimes in the fact that, you know, we are using the same systems where you would be able to generate myurana if the system allows it, the disorder is good. But that is also a place where you can just do a lot of very interesting physics experiments So as but, yeah, I mean, if we if we start looking there and we find something, maybe Yeah.
Charlotte Bøttcher:Maybe then we'll die. Yeah.
Sebastian Hassinger:And the high TC materials, do you think that it's possible to to actually implement a a qubit at that with that type of material, if if you could understand the the nature of the disorder to the degree where you could control it?
Charlotte Bøttcher:So, yeah, I think the high TC superconductors that have this sort of unconventional pairing that are conventional superconducting properties, it might be a little harder to get a very good coherent qubit. And there are a few reasons why that is. It's just that some of the loss mechanisms that are in these systems might just be too bad for building a really good qubit. But they could be used for other applications, and in fact, integrated with other kinds of qubits, where they could be used for these sort of couplers that also interact with the qubit. And and so there's definitely, I think, a lot of really great applications for them in the quantum computing direction.
Charlotte Bøttcher:Whether them they themselves can be a good qubit, I think, is still an open question.
Sebastian Hassinger:I see. That's really interesting. And so, I mean, do you I mean, if you had to characterize, like, what's the sort of split? Like, just to give me a sense in in a a an experimental sort of theme in your group, how much of what you're doing is is fundamental science versus sort of, building blocks for technologies? Or do you even think of it as two different things?
Charlotte Bøttcher:I I actually think that they're very, related, and and there's a great intersection that we're working in where they just, you know, they help each other. Meaning that the fundamental questions that we can answer helps us figure out how to build maybe a better qubit or a new kind of qubit. And then those systems can maybe help answer new questions in the systems that we're trying to use. So I I look at them as as highly interconnected. And I would say that, you know, in some cases we are more applied, but I I think that it's all it it goes together for us.
Sebastian Hassinger:Yeah. Yeah. That's what I find so fascinating about this moment right now is that that there really isn't any decoupling of the two. There's there these are very exotic lab instruments that are teaching us all sorts of things about fundamental quantum mechanics that help us make the lab instruments more useful.
Charlotte Bøttcher:So Yep. Yep. Absolutely. Yeah.
Sebastian Hassinger:That's great. Well, thank you very much, Charlotte. This has been really fun. I'm very much looking forward to what comes out of your group, and I look forward to the presentations for at APS next year.
Charlotte Bøttcher:Thank you so much. Thank you.
Sebastian Hassinger:Thank you for listening to another episode of the podcast, a production of the new Quantum Era hosted by me, Sebastian Hassinger, with theme music by OCH. You can find past episodes on www.newquantumera.com or on blue sky @ newquantumera.com. Thanks again to the support from APS for this episode. If you enjoy the podcast, please subscribe and tell your quantum curious friends to give it a listen.
