Caltech Science Exchange Presents Conversations on the Quantum World: The Power of Quantum Materials

Caltech Science Exchange Presents Conversations on the Quantum World: The Power of Quantum Materials

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Good morning. And thank you for  joining us. I'm Ann Motrunich,   a writer in Caltech's Office of Strategic  Communications. Welcome to Conversations on   the Quantum World. This series is hosted by the  Caltech Science Exchange, and designed to give   all of us a chance to hear directly from Caltech  researchers who are advancing quantum science   and harnessing it for future technologies.  We are joined today by Nai-Chang Yeh,   Caltech's Thomas W. Hogan Professor of Physics.  Dr. Yeh's research centers on quantum materials.   She engineers, measures, and creates these  materials at the nano scale. Dr. Yeh has  

co-directed Caltech's Kavli Nanoscience Institute,  and is especially interested in the unusual things   that electrons and light do in these materials.  Professor Yeh, thank you for joining us.   Pleased to be here. Let's dive right in and do some   scene setting. Can you tell me, when engineers  and physicists make new materials in electronics,  

what kinds of sizes are they now  working with? How does that look?   Typically, the sizes that people are working  with these days are mostly at the nano scale   or nanometer scale, which is a few billions  of a meter. A scale that's related to   the size of molecules, or a few tens  of atoms. To work at this lens scale,   special tools are needed because they're so  tiny. You will need to use special tools to image  

the tiny structures, or even to fabricate devices  at such scales. And some of the tools that you can   use include electron beam microscopy, lithography,  focus ion beam microscopy, lithography,   and also there are other things like scanning  tunneling microscopy, atomic force microscopy,   nano scanning optical microscopy. And given  these, the tiny sizes of these things,   they're even smaller than typical dust  particles. And so, that's why people will   have to often do these observation and  fabrication in clean room environment.   That sounds like kind of a wonderland of  machines and equipment. You've told me before   that at those scales, everything's  quantum. What do you mean by that?  

Basically the mere existence of materials  is based on quantum mechanical principles,   because at atomic and nano scales where quantum  mechanics actually, quantum physics takes over   from classical physics. And so, for instance,  light and electrons, they actually would accept   the quantum phenomena such as particle wave  duality, and they also obey the uncertainty   principle. And so, for instance, we would describe  the behavior of electrons in materials instead of   like rigid particles, we would describe them in  terms of wavelike probabilistic distributions.   And these are known as wave functions. And so,  materials are actually held together because   electrons distribute like wave functions  are holding structures together. And so,  

that's completely quantum mechanical. And also, if  you another example, you can place an atomically   sharp tip very, very close to a sample surface, a  conducting or semiconducting material surface. And   if you place it very close, but with a vacuum gap  only like on a nanometer scale or even smaller,   then electrons actually can tunnel between  the sharp tip and the underlying sample.   Which is again, quantum mechanical. It cannot happen in classical physics.  

And this is actually the principle  of scanning tunneling microscopy,   for you to image and to manipulate things down  to atomic scale. On the other hand, for photons,   for light, you actually don't think of them  as waves in the quantum mechanical scale now,   you think of them as photons. Photons are actually  quantized units of electromagnetic energies.   And so, they can interact with materials and  materials can absorb photons or emit photons. So,  

these are also quantum mechanical, and these  concepts actually are essentially ... Are   essential to a lot of light related applications  of devices, et cetera, these space.   So, things that we take for granted at the scales  where we live, things that seem continuous to us   are discreet and jumpy at this quantum scale. Yes.  

And now, if when we get down to  those scales everything is quantum,   what is meant by the term quantum materials?  If every material is quantum, then   how do quantum materials ... How is that  different? Does it depend who you ask?   Okay, so quantum materials, give you a  little historical background, it was a phrase   originally invented by researchers in condensed  metro physics. They referred to materials,   particularly called strongly correlated materials,  which are related to ... It's an umbrella term,   referring to materials that actually  have properties that cannot be easily   described by semi classical approach, or  the low level quantum physics. But nowadays   people actually generalize quantum materials to  other things, including topological materials,   low dimensional materials, and  engineered quantum materials.  

So, for instance, strongly correlated materials,  I'm trying to explain a little bit, please bear   with me because these are a little bit of jargons.  But let me try to explain them more simply.   Strongly correlating materials include something  you are probably familiar with, high temperature   super conductors. These materials, their  electronic properties are actually interdependent.   So, unlike simple materials like noble metals,  or typical semiconductors, strongly correlated   materials cannot simply be understood by looking  at one property or just approximate the rest.   The electronic charge, spin, and orbital  degrees of freedom, as well as the background,   ionic motions are all interdependent. So,  these are called strongly correlated materials.   They're very kind of hard to deal with. You  have to create new theory to understand them.  

And then the topological materials refer to  materials that have properties that are in variant   under topological deformation. And these materials  exhibit very interesting properties on the surface   that actually reflect what they are in the bulk.  But these properties can be very well preserved,   not sensitive to imperfections. And so, they can  be useful for various things. Those dimensional  

materials refer to materials that can exist in  dimension smaller than three dimension. So, such   as in two dimension like graphene, you probably  have heard of two dimensional sheets, or one   dimensional nano wires such as carbon nano wires,  or zero dimensional dots, like quantum dots,   they're related to semiconducting nano crystals. So, these are low dimensional materials usually   because of quantum confinements. So, they always  accept a very interesting quantum properties. And   then you can start combining them together to  create category structures, and have even more   interesting properties. And then another class of  materials are called engineered quantum materials.  

For instance, you can use a laser to cool atoms  or ions, and arrange them into a few tens or   hundreds of them into some special structures  that you desire, or you can use nano fabrication   techniques and make things down to very, very  small scale, which can create new properties.   And that originally may not exist in the original  materials. So, these are called nano engineered,   or engineered quantum materials. And so, but  often we can combine different techniques,   or we can grow materials also down to atomic  layer, one atomic layer at a time. So,   the definition of quantum materials these days are  much broader than what it was originally created.  

I want to go back on a couple  of those things, and just ask   a couple of clarifying questions. One  is, could ... For someone like me,   when you say that these topological materials  in that kind of middle category are in variant   under defamation, does that mean if you reshape  them they stay the same in their properties?   Okay. This reshaping, if you want to  describe it literally, that's one way of   visualizing it. But the reality in real  material system is that if you think about  

electronic wave functions, and so if you run into  impurities it's like there is some deformation.   And then, because you have some special  topological properties that are non trivial,   so those properties will not vanish when they  encounter imperfection and being deflected. That's   probably the way I would describe it. Yeah. Okay. And then going way back to the beginning of   your answer, there was one thing I wanted to touch  on because I've read about it in other places.  

You said they can't be described using ...  I think you said they can't be described   using semi classical approaches. And if  you could just explain for some of us   the sense of what classical, semi classical,  and quantum are. I think that would be helpful.   Okay. Semi classical, so this is a little  technical, but let me try to explain it a little   more simply. So, this is so-called single particle  approach. So, if you have a many body systems,   so in materials we have many, many, many atoms,  it's about 10 to the power of 20 to 23rd.  

It's an enormous number of particles, but the  semi classical approach is such that you try   to describe the electronic properties, how  electron moves around, behave, and then you   can average all of the background into some  effective property. And then you describe how   your one electron move around in this effective  background. But in strongly correlated systems,   then it's not so easy to do it that way because  it's not going to be quite accurate. Yeah.   Great. Thank you so much. Are we  already using quantum materials?   Are there any in my phone, for example? Oh yeah, absolutely. Tons of applications already,   but before I describe the examples of applications  that quantum materials have been used, I need to   emphasize an important point. That is, quantum  materials are not only used useful for quantum  

technology. They can be used for everyday things.  And so, let me take the first example, which is a   low dimensional system and also a strongly  correlated system, that is typical semiconductors   are not classified as quantum materials. But  you can take two pieces of the semiconductors   and make them into sync films and light them on  top of each other. Then you creating interface.   When you do it right, what you can do is you  can create a sheet of two dimensional electrons.   And these two dimensional electrons are  strongly confined. Now, you will apply   a strong magnetic field vertical to the planes  then they actually turn do a very, very strong   magnetic field that's vertical to the plane. And then you create very, very strong  

electron confinements by the magnetic fields,  and then they will create quanti steps   of transfers resistance. And such resistance are  so precise, the resistance values are so precise,   that they are now being used by National Institute  of Standards and Technology as resistance   standards to one part in a billion. Yeah, ne  part in billion kind of accuracy. So, this is   good for meteorology, for instance, strongly  co-related systems, low dimensional systems.   And there are other low dimensional systems  that are already being used, like graphene.   Graphene is also already used for a lot of things  such as in energy storage, additive manufacturing,   surface preservation, electronics, textile, and  printing technology, and a whole bunch of things.   And also another low dimensional systems will be  like quantum dots. There are semiconducting nano  

crystals can be used for light imaging dials,  photovoltaics, high definition television and   display, photo detectors, photo conductors,  biomedical and environmental applications,   single electron transistors. So, many of  applications. And also strongly correlated   systems like high temperature superconductors are  already being used. For instance, they're used in   scientific magnets already at National  High Field Magnet Lab in Tallahassee,   and also they're used for power cables,  transformers, although in a smaller scale,   and also motors and fault current limiters,  and also filters, and being used in   nuclear magnetic resonance and magnetic resonant  imaging technologies. And then of course, as we   shrink all of our transistors down to smaller  size transistors and devices, they are naturally   entering into the quantum regime. And so, there  is quantum confinement effect, and those systems   can also be classified as quantum materials.  So, you can see they're being used already.   That's a lot more use than I  realized, actually. That's a lot.  

And I think you and I, in conversation a while  ago over tea, we were talking and you said,   "The future is just inextricably  linked with these materials."   And I thought that was so interesting because  they've seemed very exotic to me. Clearly they   are not as exotic as I thought they were, if  they're already in so much. But can you tell me   what are these materials better at? Why do we want  them and why are they so important to the future?   Well, because right now, for  instance, one of the major challenges   in advancing semiconducting technology is that we  need to continuously decrease the size of the nano   electronic components and devices. That leads to  new challenges in the quantum limit. For instance,  

we have issues related to quantum conductance,  quantum capacitance, quantum fluctuations,   as well as increasing heat is the  patient and many materials issues   associated with shrinking the dimensions. Now, if  we incorporate quantum materials, we can actually   introduce additional electrical  and thermal conduction channels,   and providing protection barriers and layers to  prevent atomic migration in nano devices, and   nano structures, and interconnects. And also  these materials, they have interesting properties   you can combine with ... You can do proper  design to develop additional functionalities.   And so, through clever designs and  hetero structures, or inter layer   properties. And so, all of these can lead to  potentially higher densities of smarter devices   with better operation efficiency, speed,  faster speed, and lower energy consumption   for smaller and smaller volumes. And so, that's  becoming an important challenge for, at least  

for the nano electronic applications. And of  course, there are many other areas. As I mentioned   earlier, they're already been used in applications  because they have very special properties. And so,   one can design and manipulate things down  to nano scale to achieve things on demand,   achieve properties on demand. So, it sounds to me as if   quantum is both, forgive the metaphor, but the  bad guy and the good guy in this scenario. That   as you shrink these technologies, you run into  these quantum effects that are super perplexing   and hard to deal with. Atom's migrating where you  don't want them things happening. And the best way  

to solve those problems is actually to introduce  controlled quantum effects. Is that a fair ...   Yeah. Yeah. So, once you know what's going  on at the quantum scale, then you know how   to overcome issues or take advantage of  special properties at the quantum scale.  

Yeah. I think people will want to  know about the link between quantum   materials and quantum computers, and  they are interdependent. Are they not?   Kind of. Okay, so now let me elaborate.  And so, currently the most scalable,   I mean, as you know, to make quantum computers you  need to start with cubits that are quantum bits.   And of course, not just quantum bits and you  need to have quantum memories, quantum network,   quantum transducers, all of those things. But the  most essential part is the quantum bits, and the  

quantum bits right now, the cubits, or so called.  They're currently they're made out of mostly,   the most advanced quantum bits, are made out of  superconductors. But they're a low temperature,   very low temperature superconductors. And so,  there are many issues with that. And those,   we won't necessarily call them quantum materials.  They are kind of well known superconductors, but  

there are many materials related issues, and they  only operate at very, very low temperatures.   So, that makes these cubits not very scalable.  And so, of course, as I mentioned that   some of these very interesting high  temperature superconductors, for instance,   there are quantum materials. And therefore, if  we can advance interesting and good properties   of higher temperature superconductors, then it  can certainly help the development of cubits.   But also, currently though, there are cubits  already made out of quantum materials,   such as people use quantum dots as cubits,  or they use cooled atoms as cubits. So,   these are the real quantum materials are already  being used as cubits. And of course, cubits are  

directly related to quantum computation.  But typical quantum dots and cold atoms,   so far they are not as well developed as  the superconducting cubits right now.   But that's the area that can have impact on  quantum computation. But of course, there are   other quantum materials based devices that can  actually help, things like quantum memories,   quantum transducers. Quantum transducers  who would be like you can switch between   electronic signals and photonic signals. So,  if you develop computations in the local scale,   you want to transfer signals, you want to  have photonic signals. And so, all of these  

are going to be benefit, can truly benefit from  the advances of quantum materials. So, I would say   that's probably the most direct relation between  quantum materials and quantum computation.   Well, thank you. We've talked a lot about  applications already, but are there any   other applications you wanted to mention? Future  ones? Any you're particularly excited about?   Oh, there are many potentially interesting things.  For instance, we just mentioned about quantum. So,   is quantum information technology, better  cubits for ... And also better quantum memories,  

and with scalability. And also for typical  information and communication technologies,   quantum materials can make a impact. And of  course, for nano electronics, nano photonics,   nano optoelectronics, nano lasers, these are  definitely useful for sensing, for detection,   and as devices being used in a broad range of  internet of things and in consumer products.   And also, you can develop wearable flexible  electronics also for consumer products,   but also for biomedical applications. And then of course, a lot of these   quantum materials also have special  properties for energy conversion.  

They can be used in solar cells or in fuel cells,  and also they can be used for energy storage   in batteries, in super capacitors, and also for  sustainability generally, like for filtering,   desalination. And of course, you can also make  lighter and stronger structural materials,   and you can also use them for navigation,  astronomy, meteorology, many, many things that can   all benefit from studies of quantum materials. Wonderful. Thank you. I understand that this is   one area where defects can actually be a good  thing. When you have a flaw in a perfectly   ordered quantum material, it can open up some  opportunities. Could you tell about that?  

Yeah, actually it's like the world is not perfect.  Sometimes we can take advantage of imperfection.   So, there are things called defect engineering,  for instance. So, you're going down to quantum   scale and you can actually manipulate and create  defects on demand, for instance. And this way you   can actually implement some desirable properties.  For instance, there are already examples. So,   you can have atomic scale defects that there  ... And some nano scale strained properties   in certain two dimensional materials, and they  can become quantum emitters from these sites   of strained, or create defects that you  created. So, they can be really very,  

very precise quantum images, and they can be used  for quantum information processing for instance.   And also vacancies in diamond and silicon have  also been used as they can be as color centers,   and also for sensitive detectors. So, there are  plenty of examples to utilize defect engineering.   Is it quantum emitter? I'm sorry, but  is it like a laser, or what is that?   A quantum emitter is like a  little light emitting atom.   Okay. Very, very localized, and only limited number  

of photons coming out of it. But sometimes you  want to have good control. You don't want to have   billions of photons all come out together, you  can not control them. So, these quantum emitters,   you can truly position the emitting site and  the amount of photons that come out of them.   And in diamond, you can do that with a  hole in the diamond that produces color?   Okay. There are color centers, that's because ...  Okay, this gets a little technical. Diamond itself   is known as a wide bank gap semiconductor. So, you  have a very, very wide energy bank gap. And so,   many, I mean, light with all kind ... Many range  of energies can pass through this energy gap. But  

if you have some impurities, then the energy still  is much smaller. And so, when you try to shine a   white light through it, some of the light can  be absorbed instead of going out as transparent,   because usually a pure diamond is completely  white. White colored. So, I mean transparent.   And so, that means light is not absorbed.  But if you have impurities, vacancies, then   at those sites light actually can get absorbed and  then re-emitted for certain frequencies. And so,  

you start seeing colors. So, it depends on which  color gets absorbed and that's what you have.   So, they are called color centers. Sorry, some  technical jargons. But that was a good question.   Oh, well, thank you. I really appreciate you   working with me on this. One more really general  question. And that's just a quick vision for   how the future would look different if we can  really turn the physics to our advantage here.  

Oh yeah. I think it would be a brave new world  with lots of good things. So, I would say that   it can become a new quantum mirror with  scalable quantum computers and quantum networks.   And of course, it can do fast computations and  many things become possible for technology. And   then you can have better, faster, smarter,  and smaller electronics, photonic sensors,   devices, and instruments based on  quantum materials for ... And so,   you can use them for scientific exploration.  You can use them for aerospace expedition.   You can use them in consumer products, medicine,  or even national security. And also you can have  

more efficient energies and also larger energy  storage capabilities for greener environment.   So, there are many potential good things related  to everyday life, research, and sustainability.   Nice. I'd like to ask you two  personal questions, if I may. And then   we'll just wrap up with one other question  before Q&A. But the personal questions,   one is about your advisor. You studied  under the legendary Mildred Dresselhaus,   who ... A leader in nanotechnology, in carbon  science, in electronics, and a leader in science  

itself. What do you think was the most  valuable thing you learned from her?   Yeah, I actually learned a number of very good  things, but it's just in case I'm not sure if the   audience know Mildred Dresselhaus very much.  So, let me just briefly mention that she was   actually the first woman professor in electrical  engineering and physics at MIT, and also the   first institute professor at MIT. And she has won  all kinds of honors, including National Medal of   Science, the Buckley Prize for Condensed Major  Physics, Kavli Prize for Nanoscience, and also   Presidential Medal of Freedom. She was awarded  that from President Obama. And she was also the  

director of DOE Basic Signs for some time. So, she  had made enormous contributions to the world. And   so, what I learned from her really is that she is  always very dedicated to everything she did, and   she was passionate about research, and most of all  she was incredibly kind and generous to people.   And I would say that she is like, she has achieved  a pinnacle of great scholarship. And so, in   our Chinese culture usually we regard the pinnacle  of scholarship as the best accomplishment of   a person actually. And there are three important  ingredients associated with it, in my opinion.   That is our virtuosity, and then versatility, and  virtue. So, Millie, of course, Millie Dresselhaus  

has accomplished virtuosity in her career, but  she was also very versatile in many things,   in particularly she was actually a fine amateur  musician. She played a violin and Viola. And then   virtue, that's something that usually  doesn't exist in Western culture for   great scholarship, but I mean, for great  scholarship you don't worry about virtue.   But actually in Eastern culture, we actually  consider that highly. And there is no doubt   in my mind that Millie was highly virtuous. And  so, yeah, these were very, very good attributes  

of her. And so, yeah, I learned from her,  she was a great role model to all of us   who interacted with her, whether her students  or not, people were always impressed by her.   Yeah. How did you come to her? How  did you become part of this field?  

And what keeps you coming back every day? So, I was lucky. I was just a student who   didn't know anything about anything, from Taiwan  to MIT. That was my first international trip. And   I didn't even know which professor I was going to  work with, because that was before the internet   time. I couldn't find all of the information about  professors. Millie reached out to me. She invited   me to be her student. So, I was extremely lucky  that way. But I love the field. So, I think I   got lucky. I picked the right field that I have  been enjoying things. So, I would say that study   of quantum materials actually involve exploring  and manipulating the content nature of many body   systems. But you do that in realistic materials. So, realistic physical systems. And so,  

it is fascinating, challenging,  and also satisfying for me.   And I feel that the fact that I can enjoy learning  new science from studying quantum materials,   but also design and create new properties in these  systems is something that keeps me going. So,   basically it's the fun of science, and the  relevance to technology that drives me.   And also, I consider for this reason the  field of quantum materials is truly exciting.   Well, thank you. I have been taking up all  your attention and we actually have a bunch  

of questions from audience members. So, let me  switch over to those. First off, from Alexis,   "If you want to be an investor, what  should you watch out for when you're   pitched a business based on quantum materials?" As an investor? Okay. So, I think as an investor,   why should ... At least make sure that you have  proper technical consultation so you are not   just blinded by the fancy things that are  being said. If you have very good technical  

people to consult with, then you will  know whether things that are projected or   are feasible, and can be accomplished within  reasonable timeframe. There are lots and lots   of interesting properties and opportunities,  but not all of them can be easily achievable   within reasonable amount of time.  And so, that's something that   having people to talk to, who have truly solid  technical background, would be important   From Ahmed, "Will quantum materials  ultimately replace all the old technology?"   I'm sorry, replace all ... All the old technology.  

Oh, old technology.   How transformative are we talking? It can be very transformative, but   I would say that the best world is that older  technologies and these new technologies can   coexist, because it depends on what you're  working on. So, for instance, I was talking about   these quantum materials, for instance, graphene,  carbon nano tubes, they can be used for lighter   and stronger structural materials. And then  you can use them for certain things. But it   doesn't mean that everything can be based on  those. For instance, sometimes you still need   steel beams. You still need some solid concrete.  Depends on what applications we are talking about.  

But of course, when you shrink things down  to small scale, if we really talk about on   chip applications, or if you want to do a  space, aerospace expedition or something,   you want to have lots and lots of smart devices  in a small volume, then I think quantum materials   really are the way to go, because you are dealing  with quantum science down to those lens scales.   And so, it depends on the applications.  I won't throw out old technologies yet.   Nice. I have a question here about bio-inspired  approaches. Kevin asks, "Have you seen your peers   begin to consider quantum biological  processes, like photosynthesis, as a   resource of ideas for developing technologies? Yes. Absolutely. Actually, people are working on   such things. And actually, I myself have a little  bit of involvement in using quantum materials for   potential bio applications. Recently, we have  published a paper that basically we are able to  

use graphene to protect thin layer of gold that  are typically used in wearable bio devices,   biomedical devices. And so, you can use  graphene to protect them so that ... And to   enhance the flexibility. But that's the area of  medicine, but yes, photosynthesis, cetera, people   are working on it. People are considering how to  enhance the efficiency of, say photosynthesis,   is one area of energy conversion. Yes. So, at  Caltech actually there are people working on it.   Yeah. And then we have a couple questions about  getting into this area and encouraging people   to get into this area. I think I'm going to  encapsulate them in a question from Akhanksha,  

which is, "As a teacher, how could a  person help students be attracted to   quantum physics from an early age? How should  a beginner start studying quantum mechanics?"   Okay. Beginner, how do  beginners start? Well, I think   usually people were first fascinated by the  potential of benefits that you can gain. And   I think that's one way that people realize, for  instance, these days. Young people realize that   sustainability is a critically important issue,  for instance. And then you can see that a lot   of these quantum materials potentially can  address some of these issues. So, from the   potential for making the world better, that  would be one way of bringing young people,   young talents into this kind of research. But  sometimes it's just the mere beauty of science.  

Actually, I was drawn to physics, just I didn't  even think about applications. I just love it.   But quantum science is a little more advanced  for young people, for children, for instance.   So, people need to build up some knowledge  in order to truly appreciate quantum science.   So, I think it will be the best just initially  show people all the fancy ... All the wonderful   things that quantum science can do. And then from  there, then maybe people can dig in, young people,   students can dig in, and then they started  developing for it. I don't have the best recipe  

for it, but because I was just drawn to the beauty  of science. But not everybody will be motivated   by that. People may want to know what can I do  with it, if I can make the world, make my future   better. So, that would be another motivation. But  as I said, this field has beautiful signs, and at  

the same time highly technologically relevant. So,  people can be drawn to it either way, I guess.   From Nylo, "How are devices that rely on quantum  materials made resistant to damaging quantum   processes, like even radiation?" I'm sorry, could you repeat   the question one more time? Sure. Yeah. If we have devices that rely on   quantum materials, how are they  made resistant or proofed against   damaging quantum processes?  Radiation was one example given.   How would they resist processes  that may damage the ...  

I wonder if that means, like when you get down  to this scale how do you emphasize the good   quantum processes and avoid the bad ones?  We got into that a little bit earlier.   Well, okay. So, there were  things, like for instance,   if you have topological materials, certain  processes actually are not going to be   devastating to them. But actually, I'm  not quite sure how to address this in   simple terms, because it depends on the  situation that you're dealing with. So,   you can develop things. For instance,  you can go to lower temperatures,  

that's one way, or you can add protection layers,  or something to prevent external unnecessary   photon interferences, for instance. So, it really  depends on the specific systems that one is   working on. But in general, if you understand  the properties that you care the most about,   then there should be ... You can try to  work out a way of preserving the specific   properties that you want to work with,  and try to use other things to eliminate   the interferences. Because this question  is a little too general, I don't know how   to really address it more precisely. To  me, I have to look at what I'm working on  

and then think about what kind of solution I'm  going to provide. I'm going to come up with.   So, it's really contextual  to the specific problem.   Right. Depends on what you're  working on. Yeah. Depends on   exactly which processes you care about,  what materials you're working on.   I have one question from Victoria here. "Do  topological quantum materials have advantages  

in using them for quantum  computers? What do you think?"   In principle, yes, because they are more fault  tolerant. And so, you can preserve quantum   coherence much better. On the other hand, it's  like a double edged sword. When you have something   that's insensitive, or less sensitive to external  perturbation, that also means it's much harder for   you to manipulate it. And so, if you want to  do entanglement, you want to transfer signals,  

yeah, the coherent part is very well preserved.  But if you want to do other things, it may be   more difficult. But in general, yes, topological  quantum computation will be a very exciting   direction to go if we can find the right kind  of systems to provide it. People were actually  

working hard, trying to use  something called anions,   that they are related to what I mentioned earlier.  Two dimensional electrons, you apply very strong   magnetic fields, and you turn electrons  into a new state of matter called anions.   And supposedly they have very, very interesting  topological properties, but the problem is that   it's very hard to control. And so, people I  think spent more than a decade exploring it.   And I think the progress is limited. So, right now  the best [inaudible 00:50:01] right now are still   this good old, low temperature superconductors  making into a squeeze superconducting quantum   interference devices, and [inaudible 00:50:10]  and junctions. People are using those right now.  

Just because of the difficulties of control. Yeah. Sometimes like neural nets, the ideas   are so far ahead of their time that you have to  wait for everything to catch up. I think we are   out of time for questions. And I'm so glad  that you had time to answer so many of them.   Thank you so much, Dr. Yeh. And thank  you to everyone for joining us today.  

In the next Conversation on the Quantum World,  you can find out why space might not be what   you think it is. Registration will open  soon for that event, which is July 12.   My colleague, Whitney Clavin, will interview  physicists, Katherine Zurek, and Rana Adhikari,   about quantum gravity. In the meantime, I hope  that you will explore the Caltech Science Exchange   online. It is at You  can find clear trustworthy explanations focused on   really important areas of science and technology,  areas where there might be a little hype or   misinformation, or just confusion, areas that are  in the news. It's very helpful. Beyond the really  

helpful quantum explainers, there are sections  on COVID-19, earthquakes, voting and elections,   very topical, and sustainability, also topical. Thank you again for coming today. Thank you everyone. Thank you, Ann. Bye.

2022-06-05 15:07

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