Best of: The future of ultrafast electronics

0:00Matthias Kling:Hey everyone, it's your host Russ Altman from the Future of Everything here. About a year ago, we released an episode on the future of ultra-fast electronics. It quickly became one of our most popular episodes, especially on YouTube. We're excited to re-share it with you today. Physicist Matthias Kling walks us through his study of photons and the things science and scientists can do with ultra-fast pulses of x-rays. The knowledge he's gaining could reshape fields like material science, artificial intelligence, ultra-fast and quantum computers, and medical diagnostics. We hope you'll tune in again wherever you get your podcasts.

0:37Matthias Kling:As a reminder, we post full video versions of each of our episodes on YouTube every Friday, so be sure to check those out if you haven't already. Before we get started, please remember to follow the show in whatever app you're listening to. That'll guarantee that you never miss the future of anything.

1:00Matthias Kling:So we all know that electronics are fast. Computers, fiber optics, they're operating on the scale of nanoseconds, which are one billionth of a second. There are a billion nanoseconds in a second. And that's how our computers and smartphones are working these days. But physicists have recently figured out ways to generate pulses of light that are at the scale of attoseconds, A-T-T-O seconds. There are a billion attoseconds in one nanosecond. And therefore, if you've ever heard of this word, it's a quintillion of them in a second. So what does this matter? Well, it means that we might be able to make measurements of physical systems that capture motions that are super fast and even make movies of chemical bonds forming or breaking or individual electrons emerging from the surface of a new material.

1:57Matthias Kling:It'll also lead to faster computers, including both traditional computers and quantum computers. Well, Matthias Kling, as a professor of photon science and applied physics at Stanford University and an expert at these very fast pulses of light and their applications. He's going to tell us how all of this technology might revolutionize the future of everything. Matthias, one of your areas of research expertise is ultra-fast electronics, ultra-fast photonics. What are the technologies or capabilities that are making these advances possible now? Yeah, thank you, Russ. First of all, thank you for having me.

2:37I love talking ultra fast. So when you think about the fastest processes that we're experienced to, that's, for instance, our computers, right? They run at gigahertz frequencies. So that's if you convert that to a time scale, it's nanosecond scales. So that's sort of scales that we're sort of used to, but then there's quite a few orders of magnitude of scales below that where things evolve even faster than electrons zipping around in your electronics. And that is, for instance, molecules rotating. That takes picosecond time, is on picosecond timescales, that's 10 to the minus 12 seconds.

3:19Matthias Kling:So a picosecond is a thousand times faster than a nanosecond. I'm just checking. That's right. That's a thousand times faster than a nanosecond. And then another yet a thousand times faster than a picosecond is a femtosecond. That's when molecular bonds break and recombine. And the timescales that I'm concerned with are even faster, autosecond timescales. So that's 10 to the minus 18 seconds. And it's a billions of a billions of a seconds. and you have to write a lot of zeros on the board to get to that one in the end. Yes. This is ATO just for people who are not familiar. A-T-T-O second is what we're talking about here.

4:02Matthias Kling:And if I'm keeping track of the numbers, there's a million of them in a nanosecond, which is already what our computers are operating at speed. Okay. Yeah. So, okay. And essentially one at a second compares to one second. That's about the heartbeat rate, right? As one second to the age of the universe. So just the ability of researchers to be able to look at these incredibly fast timescales is already mind blowing. And in fact, 20 years ago was, in 2001, in fact, was the magical year where two groups managed to measure the first out of second pulses, the groups of Ferenc Krauss and Pierre Agostini, based on a technique that Annelie developed that is called high harmonic generation, where you generate X-rays from intense laser interactions.

4:58and they have been awarded the Nobel Prize last year for this discovery. And there's a good reason that they were awarded the prize because these very short light flashes, they allow us to take movies. So imagine you're dancing around, right, in a disco or so, and you have that flashlight illuminating your dance, then you will see yourself in sort of still frame images dancing around the floor. And if you put them all together, you can sort of assemble the whole dance out of it.

5:26Matthias Kling:Yes. And in a similar way, if you use these extremely short light flashes that are just addoseconds short, we can actually flash them at electrons as they undergo motion in molecules or in nanosystems or whatever it is. And we can see how they move from A to B and so on. So they're so incredibly fast that we need these very, very short light flashes to sort of take a still frame image of their motion. So that's, thank you very much. So that's fantastically exciting. Atto seconds are our new favorite time unit. What kinds of things are happening in physics that you could take a movie of at atto seconds?

6:03Matthias Kling:So you mentioned that the heartbeat is every one second or so. So we can get nice pictures of a heartbeat. Since it takes about a second, I only have to divide that up, say, into a 10 or 100, 100th of a second or one-tenth of a second, and I can get a nice, smooth movie of one or two heartbeats. That's right. We don't need atto seconds to look at hearts. Oh, maybe I'm wrong. You'll tell me. At least the gross heartbeat, it would just be a very, very, very slow-mo. And many people know about this now because we all have slow-mo on our phones. If you take too many time points, it just takes forever for the heart to beat.

6:36Matthias Kling:So there must be interesting things happening at the Atto second timescale. Paint a picture for what kind of things we'll be able to see in these movies. Yeah, so imagine the first movie, in fact, that was taken was a movie that Edward Mubridge took at Stanford. Stanford University didn't exist at the time, but Stanford was this big horse farm. Yes. and the question was there if horses have all four hooves in the air as they are galloping right and they couldn't answer that question because it was just the motion was too fast and so they were debating whether this is the case or not and then Edward Mubridge had this really nice idea of assembling a set of cameras along the horse track and sort of triggering them one by one as the horse was going along the track.

7:29And so he recorded these still frame images of the horse along the track. And well, he did capture, in fact, one image where the horse has all four hooves in the air. So they were able to answer a very fundamental question that existed at the time with the first type of movie that was ever recorded. And we're taking this basic concept to the extreme. So we're looking at the fastest motions that you can imagine nowadays, and that is electrons zipping around atoms, zipping around small molecules. And so one very fundamental process we looked at, and there's actually a paper that just came out yesterday, is photoemission.

8:12The photoelectric effect is something that Einstein essentially was able to describe using quantum mechanics. and he was awarded the Nobel Prize for this discovery, for this description. And it's essentially you shine light on some metal, for instance, and what is emitted then as an action of the light impinging on this structure is an electron. Okay. And this electron has a certain kinetic energy and we can all measure that. And so you would think this was about 100 years ago, right? So at least his prize was. So you would think that this is well understood, right? 100 years of physics, I mean, we must understand this.

8:53But in fact, what was not understood until very recently, until Adam's second science came along, is how long it actually takes between the light being absorbed by the structure and the electron to come out. Yes. And this was assumed to be essentially instantaneous, right? So it was so fast that people said, okay, it's instantaneous. But that's not really true. So if you look at the details, you can find out that this electron actually, it really travels and it needs a little bit of time to come out. And the interesting thing is that the time it takes to come out has a lot to do with what kind of environment it's in, right?

9:32If it's in a molecule and an atom and how many other electrons are around and how it kicks around other electrons and things like that. And so this is quantum mechanics at its extreme. we're looking at the timescale it takes an electron to come out, for instance, of an atom as we shine light on it. And this is something we can measure. And it takes just about, let's say, 100 autoseconds to this latest measurement went all the way up to 700 autoseconds. And it tells us about the system. And so we can compare this to very detailed, very hard calculations. In fact, the data that we just published existed since about now.

10:08It was 2018. So that's six years ago, right? Six years ago, we took six years for the theory to catch up. So I like these experiments where we get the data and then theory is scratching their heads and they're like, oh, how?

10:23Matthias Kling:I need to explain this. I need to have a theory that makes. Yes. Okay. So that sounds fantastic. Let me just pause and make sure we understand. So are you taking movies of multiple electrons leaving the surface and then averaging them to get a sense? Or are you able to actually observe like individual movies of individual atoms leaving the surface? Yeah. So this is interesting. And this actually brings me to free electron lasers. Because there have been experiments that these Nobel laureates did since the invention or the birth of Atasek and Science using just normal tabletop setups in their labs.

11:05And in that case, they looked at what's called valence electrons. So these are electrons that are sort of the least bound electrons in some sense, and they're the easiest to remove. Yes. And they're typically, they're not very localized, right? So if you imagine you have a solid or you have a molecule, these electrons, they don't sit just on one particular atom, but they have some kind of delocalization over the whole structure. So your question is a very good one because using these tabletop techniques, it was very hard to answer where exactly that electron came from.

11:38Matthias Kling:Yes. Now we can use x-rays at much higher energies. And these x-rays penetrate very deep into atoms, very specific atoms. We can tune the energy just to, for instance, a nitrogen atom, an oxygen atom, things like that. And then look at the photo emission from that particular atom in a very large molecule. So we're very specific. Wow. Yeah, very sort of medical insertion in some sense. So it's very specific in what we can probe. and it's really great because the more specific we can look at where something is happening the more detailed the movie of course is that we will record in the end and the more detailed the comparison can be to the theory that we're trying to push ahead right because in an ideal world theory can explain everything so since we're talking about the future of everything you would hope that one day we have an ai and it uses uh theoretical calculations that are so advanced that we don't need to do experiments anymore, right?

12:36Right.

12:36Matthias Kling:I think this is actually my goal for biology as well. Yes. So my personal opinion on this is we'll never get there. But that's also because we're asking more and more complicated questions, right? So simple questions, probably theory, like if I drop an apple, right, and I let it fall to the ground, I can pretty much well predict when it arrives on the floor. But for complicated enough questions, theory has to make assumptions. And especially true for quantum mechanics. If I look at very complex systems, I need to make a lot of assumptions to describe what an experiment gives me. And so this interplay between experiment and theory to kind of push each other to develop the theory and make it better and to help us use then this sort of basic understanding to make much better materials, for instance, for solar cells, much better catalysts for producing new fuels and things like that.

13:31So there's real world impact in this very fundamental understanding that we are reaching.

13:37Matthias Kling:Yes, I've had guests on the Future of Everything podcast who are doing material science or electronic batteries. And it's always impressive to me that there is still a very empirical aspect to these fields. This is not a criticism, but the experimental work is very important because they don't always have the supporting theories. So what I'm understanding from you is that these measurements will give you the basis for the theories where they may be able to have a little bit more of an idea before they go into the laboratory of what to look for or what to build to get the properties that they're seeking.

14:14So this is definitely true for autosecond science. The field has evolved quite a bit in the last 20 years. So in the early days, people were happy to just understand what an autosecond pulse looks like and to be able to produce this very short light. But nowadays, the community is very brave. So we're looking into microelectronics. We're looking into medical applications. Ferenc Krauss, as an example, is looking into using some of the techniques developed in the field for what he calls molecular fingerprinting. So essentially, you shine the light through a drop of blood. You record the sort of light wave that comes out.

14:51and then from the exact sort of wave nature that you record from that, you can infer what type of diseases you have, right?

15:02Matthias Kling:Yes, because there are specific molecules that have a kind of, as you said, you use the word signature. These molecules have a signature that is unique and you can detect. Okay, let me ask a few questions about that because now you're getting close to things that I maybe understand fully. One of the things about living systems and blood is it's at room temperature or it's at body temperature, and the molecules are moving around a lot. And you were talking about focusing on – earlier you were saying you could focus on an individual nitrogen. That implies to me that you're going to have to do something to keep these molecules from moving too much, but maybe not.

15:38Matthias Kling:So is the issue of temperature – like do you have to freeze everything to make these measurements, or is room temperature or body temperature within range? So this is an excellent question because you're already motivated why it's interesting to study systems at the temperature where they're functioning in the body, right? So ideally, we don't want to have to freeze structures out to study their behavior because it will be very particular to that crystalline structure we created. And it might not reflect what we see in the real world, right? This interview would be very different if both of us were frozen.

16:14For sure. Exactly. So that's a good example. And in fact, this is where these X-ray free electron lasers come in. They can produce, and I have to back up a little bit to explain what that is. A free electron laser is essentially it starts with a linear accelerator that accelerates electrons, these tiny quantum particles to very high energies for the experts in the audience. At the moment, with our new superconducting accelerator, we can go up to four giga electron volts and in the future will be eight giga electron volts. So these are very, very high energies. And then we send these very high energy electrons through what's called an undulator.

16:56It's essentially a periodic magnetic structure that forces the electrons to wiggle, to oscillate a bit. And electrons don't like to oscillate. They essentially emit radiation as they do so. It's called synchrotron radiation. And using a few tricks, we can actually, in these three electron lasers, we can amplify that radiation. We can make it coherent instead of incoherent, how it's called. So it becomes laser-like. And so it really gains a lot in intensity. And these FELs, they have an incredible increase in brightness, in intensity over synchrotrons that have been generating X-rays for decades.

17:39And X-fels are around just since about, well, SELS has been around since 2009. So that's when the first experiments have been conducted, when it saw first light. our new superconducting accelerator was actually commissioned and taken into operation just last year and so it's a relatively young field and now we can use these extremely bright x-ray pulses imagine you know this is cannot at all compare to what you have at your doctor's office it's first of all it's laser-like which helps a lot with detecting for instance information that helps you to build 3D images instead of just projecting. So when you take an image of your tooth, let's say, at the dentist, sometimes it's really hard to see the details, right?

18:23When you use laser-like radiation, you take the same image. Even I, and I'm not a dentist, right, I can tell what I see because it's so short, and you get that sort of depth information, so you get 3D images. And this is sort of the type of radiation we generate, just a lot brighter. And it's also very short. So the pulses we get from the XFEL are, well, we can tune them. We can nowadays generate out-of-second light pulses. It's actually something that was invented here at LCLS by Argo Marinelli and James Krein, some two really fantastic scientists at the lab. And with these extremely short light pulses, we can, for instance, illuminate a biomolecule, Yeah.

19:07And then take an image, a diffraction image, X-ray diffraction image in one single shot. So one single X-ray illumination gives us the structure. And now imagine in real life, in nature, you don't just have that one structure. You would need to freeze it out to have that just that. You have many different ways how the protein could look like depending on temperature, depending on the environment and so on. And so what we do at these XFELs is we take all of these images. So we let the system at room temperature. We maybe stimulate some dynamics like we mix something in and then this thing folds or it catalyzes something.

19:46So enzymes are things that we look at. And we are following all of that at the same time. So essentially, we're taking these multitudes of images of all the things that are going on at the same time. And then we can use that information to really tell what nature is doing. And one of the really exciting things that nature is doing is to actually generate the oxygen that we breathe. So one of the most investigated and one of the success stories of these XFELs is the study of Photosystem II. It's essentially a system that sits in plants and is using just water and sunlight to generate oxygen. Somewhat key for life on Earth.

20:28Exactly. And everyone knows that. But the exact way how this is happening, this catalytic cycle is very complicated, has a couple of steps that people knew about, but they didn't quite know how the structure looks like and how it functions in reality. it was really possible at these exfels to study that for the first time. So now we have a sort of very fundamental understanding of how Photosystem II is generating oxygen from breaking up water with just sunlight. And this is, of course, amazing because if you, in fact, if you want to generate water as oxygen from water using our human technology, right, not what nature is doing, we would need to use very high electric currents or temperatures or whatever it is.

21:22It would be very, very inefficient as a process.

21:26Matthias Kling:So we're learning nature's secrets by looking at and taking movies as it happens. That's right. This is the future of everything with Russ Altman. more with Matthias Kling next.

21:47Matthias Kling:Welcome back to The Future of Everything. I'm Russ Altman, and I'm speaking with Professor Matthias Kling from Stanford University. In the last segment, Matthias explained to us some of the new capabilities in generating very rapid bursts of light that can control electrons and can make measurements on physical materials that allow us to see them move and change in real time. They're making movies that are super, super slow-mo. In this segment, Matthias will tell us a little bit about how all of this will lead to faster computers and electronics. He'll also tell us what the role of AI and machine learning is in all of these endeavors.

22:28Matthias Kling:So, Matthias, I wanted to ask you about an area that actually you're an expert in, which is ultra-fast electronics. Very early in the conversation, you referred to the fact that our current electronics are operating at a nanoscale timescale, but we've now been talking about out of seconds for quite a while. Is there a possibility of using that speed for our next generation of electronics? Yes. Thank you for this excellent question. So, I'm very passionate myself about advancing the speed of electronics. And one of the ways we dream of doing this is to use the waves themselves, the light waves themselves, and that electric field that the light wave has to steer electrons in circuitry.

23:13So at the moment, this is done just by applying a voltage and then you shift electrons around in these wires. And typically, there is some resistance that limits the speed. There is also other sort of limits. And so, in fact, the transistors nowadays, they have reached gigahertz level frequencies. So they're still operating at that nanosecond scale. But we dream about pushing that all the way to the autosecond scale, which in frequency space would not be gigahertz. It would be not even terahertz, but the next level, which is petahertz. And so you might wonder how far could we ever go? Well, there is a limit.

24:00Moore's law is going to have a limit. And the limit is essentially the speed of light. So you can't be faster than the speed of light. This is a very fundamental law. And essentially, as soon as we start moving electrons around at almost the speed of light, that's how fast we can go. But we're very, very far away from that. So we're about a million times below that speed. And so we want to use these light waves that actually the autosecond community has done a lot to produce light waves that are very well controlled, that are controlled to a minute detail on their actual sort of wave nature on the sub-cycle evolution.