The Exchanges

Q low, but it happens enough. That the antiparticle actually starts to delete part of a black hole, and that's how black holes evaporate, and they have this theory, all these interesting things, but can you tell us how, what quantum tunneling is? So this is another one of these sort of features of quantum mechanics that arises from the fact that these things are kind of waves and probability functions.

A Yeah, so if, if you have, um, if you have an electron just traveling through space, hitting, hitting a wall, let's say, There's a little wave, wave packet wave function to it. So it's not a single particle. It has some extent to it. And what happens is that when that particle hits the wall, Quantum mechanics say there is some amount, small amount of this wave function, or if you like, the particle going through the wall, and then to the other side. Now, most of the time, it, uh, it bounces off, but every once in a while, it goes through. And you know, this is seen in, um, uh, everyday devices. This is not, if you build very small, um, memory circuit, you have to worry about Electrons tunneling and charge leaking off your capacitor. They have magnetic memories that depend on these tunnel junctions. So this is a very well-known phenomenon. If you make the, this barrier, this insulator, just the, you know, 10, 20 atoms thick, then that's thin enough for it to go through.

AI assessment note: “when that particle hits the wall, Quantum mechanics say there is some amount... going through”

Q And then Leggett proposes this idea. Maybe you can share a little bit more now that we've got, I think, a bit of the basics on what was discussed, which was zooming out a bit, like, rather than just think about all of this happening at a microscopic scale, is it possible for it to happen at a bigger scale?

A Yeah, and again, we've been talking about quantum mechanics as the physics nature at this microscopic atomic scale. But the question was, if you made a macroscopic object, would it obey quantum mechanics also? Okay. And then, you know, that was the basic question. And it turns out that there's a very natural system to look at, looking at an electrical system and look, seeing for quantum mechanics and electrical system where the currents and voltages of essentially electrical oscillator, does it behave like a classical physics or does it behave with this quantum mechanical nature to it? And that was the question. Now, it turns out that when you think about quantum mechanics and thinking about, well, there's the quantum behavior, but then at some point you have to measure it, which then turns it into a probability. There's something called the Schrodinger-Cat paradox, where, um, in the paradox you have a, you radioactive decay, and then you, you, You let it happen for, let's say, half of the radioactive decay time, and then you say, and then you have a radioactive decay, a detector, and then a bottle of cyanide, which will kill a cat. And then do you say, you know, after some amount of time, is the cat in the dead and alive state? Ok, and, you know, physicists, you know, and this is a, this is a good question. Einstein brought it up, Schrodinger brought it up. A lot of people, uh…

AI assessment note: “if you made a macroscopic object, would it obey quantum mechanics also?”

Q Where are we in quantum computing evolution today? So what's the state? At what point will we have, call it generally accessible and generally useful quantum computers that can do all of the amazing things everyone's kind of talked about for decades that one would be able to do?

A So that's right. So, um, right now we're, we're about the 50 or a hundred qubits for the superconducting case, but they, They can be fully controlled and run real algorithms and do very complicated things. They have a lot of other systems that can do that. I think the newcomer on the block, which looks good as neutral atoms, where they made big neutral atom systems, but they're still working to get the gates controlled really well and the like. But what's happened right now is we can run genuine algorithms on that. And people have, ah, have, you know, have ideas they want to run, but because these qubits are not perfect, okay, it's an analog control system, and fundamentally, these quantum bits have a little bit of error to it, a little bit of noise to it. You can only run so complicated of a project, and it's good enough to write scientific papers, and Try things out. Uh, every once in a while, people say they've done something, uh, you know, uh, that's hard to compute, and well, that's fine, but they aren't really big enough to be useful yet. They have to get bigger, and they have to get better. Less noise.

AI assessment note: “they aren't really big enough to be useful yet. They have to get bigger”

Q And then just to understand your work that you won this Nobel Prize for that demonstrated this quantum mechanical phenomena at scale, is that Part of the design of a qubit and the circuitry. Did that inform that design work or explain it rather? Yeah.

A Yeah, it was the very basic simplest circuit. Uh, you know, I'm, we were using analog simulators at the time, not even, I, I took data with a computer, but this is, this is far back enough that, you know, it was very rudimentary. And then over the years, we just got more sophisticated design by the whole field. You know, many, many people. And, uh, and we were able to put things together in a way to actually build a computer. Now, I would say the reason why it's interesting from the Nobel Prize thing is what it led to. And what it led to right now is a thousand, maybe several thousand people around the world Doing research to build this superconducting quantum computer. And, and it just turned into enormous field, large number of papers, large number of people, people selling quantum computers, IBM is selling quantum computers, people are selling time on the quantum computers, and the fact that it was a, it was a useful idea, ok, that led and, and, and brought into form, uh, uh, all, all these different experiments, ideas, and many, many people contributed this.

AI assessment note: “Yeah, it was the very basic simplest circuit.”

Q Do you have a point of view on the timelines? This is everyone's speculation, and there's been more hype than reality.

A Yeah, there's more hype than reality, and, and, uh, And it's hard. I used to not want to speculate that, but since I started a company, then I can do that. And what we want to do, and it's a timeline of many other groups, is to do something in, let's say in the next eight, 10 years, something like that. But the problem is, you know, people are predicting 10 years, you know, for a while now. So, okay, we, we have to do that. But, um, I can tell you for what we're doing, Is that we've identified what are kind of the technology bottlenecks of the current fabric, current ways to make a quantum computer. We've written some papers on it. And, um, you know, we're working with people in the semiconductor industry to manufacture this in a much more cost effective quality way, you know, the way you make these GPUs or something. And we think, uh, you know, when we get that to work, we can scale up very rapidly. So in, in, in, let's say 10 year time scale, something like that.

AI assessment note: “is to do something in, let's say in the next eight, 10 years”

Q technically difficult fields like fusion energy, perhaps even quantum computing, they're seeing profound acceleration in getting to their crazy big goals on these very big technical projects because of AI. Is AI starting to play a role in solving some of the engineering, material science, scaling, noise issues that we've seen historically in quantum computing, and do you think that there's an acceleration underway in performance improvements because of AI?

A There, there may be, um, my particular, and, and, and there's things we can maybe do modeling and the like. We also think what we can do is use the quantum computer and AI together to solve the problems better. So that, that, that's what our theory team is proposing. I used to work with Google quantum AI. That's what they're proposing. So there's a general feeling of that. My particular view though, is that in terms of this control, if you don't build your system cleanly enough, and you know, that the control is clear enough, uh, you're, you're not gonna get the, the great performance out of it. So I'm a little bit old school here, and, and working on, you know, building it that way. There's certainly some elements where you can use AI, You know, in the decoding circuit for the, the error correction and the like. But the one thing to mention to you is that, you know, these qubits are, are naturally very noisy, and you can maybe do Sometimes a hundred for bad qubits and maybe a thousand, maybe few thousand operations before they kind of lose their memory. You know, you can think of it as like dynamic RAM where you have to refresh it. Well, you have to refresh it with error correction. And because of that, you're talking about a million qubit quantum computers to be general purpose and solve really hard problems. There might be some million. A million is a good round number for i…

AI assessment note: “There's certainly some elements where you can use AI, You know, in the decoding circuit”

Q What did you go on to do at that point? Was it considered groundbreaking, Nobel Prize-winning Work, and what was the story at that time when this came out?

A Yeah, so, you know, it was an, it was an important piece of work, and people noticed it, but, you know, it, it, you know, we, we showed that quantum mechanics worked, and quantum mechanics worked on the macro scale, which was nice, but one could still, you know, argue, well, what is it good for? What are you going to do? And the, in fact, the secret of an important scientific breakthrough Is does it lead to other experiments and other papers and other inventions and the like? And, uh, that kind of took, uh, you know, many decades to happen because it was so new and people had to do, do that. So I would say it was noteworthy at the time, but, you know, not necessarily, you know, something for a Nobel prize because it was just kind of, you know, weird and went off and, you know, what are you going to do with it? Right. But what happened at the time was very interesting. And at the end of my thesis time, there was a conference in, uh, UC Santa Barbara, where I came here for the first time.

AI assessment note: “it was noteworthy at the time, but, you know, not necessarily... for a Nobel prize”

Q Where were you when you got the news this week that you won the Nobel Prize, and how surprised were you? Because this is a forty-year-old research effort. Had anyone given you a call, rumor, gossip mill, saying, hey, you're on the list this year, potentially being considered?

A So let me give you a little bit of the inside story. Um, you know, if you, we, we've known that this was an important experiment from the beginning. We've attained some other prizes that are, you know, much less well known and really appreciative of all that. And you, you, what happens is the Nobel, um, um, system, uh, put together, uh, Nobel symposiums where they get together physicists in a certain field, which is quantum information and this kind of thing, and they, they give, uh, have all the scientists give talks and, and they want to kind of check on the vitality of the, you know, of the field. How big is it? And then, you know, also maybe some of the, the leaders that maybe think about it, you know, can they give a good talk? Would they be a good representative? So, um, uh, Michelle and John and I have been to these, uh, symposiums before, and we kind of knew, you know, what was going on, you know, that at least we were considered. And I'll just tell you, as a scientist, just to be invited to these and be considered is a, is a fantastic honor. You know, and, and having, giving the prize is just so kind of unbelievable that you shouldn't think that way. So, you know, I've known about it for a few years, and in fact, to be very honest, in the past, when the dates have come around, it's like, oh, is this gonna happen? And then you wake up in the morning, and it's like, oh, …

AI assessment note: “we kind of knew, you know, what was going on, you know, that at least we were considered.”

Q So this Josephson junction is two superconductors. They're on either side of a barrier that you create. An insulating barrier. And then maybe just explain the experiment and, and what you guys measured. And this, this was all while you were in grad school, right?

A Yeah. Yeah. And, and, uh, and this is, uh, this Joseph junction because the Cooper pairs have to tunnel through it, but they kind of tunnel through it together without any loss. This, this actually forms what's called an electrical inductor in circuit in circuits. So an inductor is normally a coil, a wire that stores energy in this magnetic field. Here, this, this just stores energy of the electrons tunneling through here. It's so, it's a, it's something called, we call it kinetic inductance, and it happens with this. But that forms a nonlinear inductance, and with a capacitor in the circuit, that forms an inductor capacitance resonance circuit. Which is in your old, which is like in your radios, you have filters of LC resonance circuits to filter your signal and do anything. So this is a very common microwave and, you know, radio frequency element that you use all the time to make electrical circuits.

AI assessment note: “This actually forms what's called an electrical inductor in circuit in circuits.”