Short Wave - Quantum Mechanics For Beginners

Episode Date: October 19, 2020

Monika Schleier-Smith, associate professor of physics at Stanford University, studies quantum mechanics, the theory that explains the nature of the itty bitty parts of our universe: atoms, photons, and individual particles. It's the science responsible for innovations in computers, telecommunications, and medicine. Schleier-Smith was recently awarded a 2020 MacArthur Fellowship for her work in the field. It's research that often starts in a lab and as Schleier-Smith describes, requires both troubleshooting and optimism.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, everybody. Maddie Safaya here. And Emily Kwong. Okay, Maddie, today I wanted to go in a slightly different direction and broach a field that we don't often. Oh, is it math? You're so scared. Close. Oh, God, is it physics?

Quantum physics! A.k.a. quantum mechanics. So this is a theory with tech. technological applications you may appreciate. Lasers. Love them. MRI machines, fiber optics, the computer industry. All right, Kwong, all right.

Has aspects of quantum mechanics in it. The future is possible because of quantum mechanics. And this scientist is on the cutting edge. My name is Monica Schleier-Smith, and I am an associate professor in the physics department at Stanford University. This year, Monica was one of the recipients of the MacArthur Fellowship, unofficially known as the Genius Grants. And she got this big news from MacArthur on a particularly strange day. I'm in California, and it was a day when it just never got light outside because of the smoke

from the forest fires. So it felt sort of like the apocalypse. It was midday, but it felt dusky outside. And I was sort of sitting there about to start the next Zoom meeting and I got a phone call. The phone call. The MacArthur Fellowship is a no-strings-attached award of $625,000 designed to recognize really pioneering individuals. And full disclosure, the MacArthur Foundation is a financial supporter of NPR. Monica had to keep the news a secret at first. Well, I was allowed to tell one person and I told my mom. I knew it would make her happy. And I knew she wouldn't tell. I don't know, Monica. Moms want to brag. Yes, yes. Her mom was so proud. She wanted to know about past winners.

There's been a lot of artists and writers, people in the humanities and public life who have won MacArthur's. But scientists are really creative people, too. And as we're going to talk about, you've got to be creative to do what Monica does. Artists and scientists alike are sort of driven by just a passion for pursuing something

that deep down inside, they have this sort of instinct, that there's something exciting there. But they're still figuring out exactly what it is. Today on the show, Monica Schlyersmith takes us into her laboratory of lasers and mirrors to break down what's at work. And how her innovations in this field have already changed the world as we know it. You're listening to Shortwave from NPR. All right. So today we are delving into quantum mechanics with Monica Schleyer Smith, a MacArthur fellow.

Right. So quantum mechanics is a very well-tested theory that explains the nature. of really, really small things. Think atoms, photons, individual particles. And they don't fully behave according to the laws of classical physics. But do you know what theory does describe their behavior? I'm guessing it's quantum mechanics. You guessed correctly. Yes.

And Monica has been curious about quantum since high school chemistry class. I remember my teacher actually giving these very very, at analogies saying an electron and an atom, it's not just at a point. I should think of it as smeared out because of quantum uncertainty. He used to say it was smeared out like peanut butter. I like that analogy. Because it's so hard to bend down exactly where an electron is in an atom. That's why we think about it more as a smear than as a single point. Got it. And quantum mechanics is a theory that describes this uncertainty, this peanut butteriness. Monica took her curiosity for this subject all the way to grad school, where I could actually kind of play with quantum uncertainty in

the lab. That was fascinating to me. That's amazing. Your mind is just because some people do not like uncertainty. That's right. We don't like uncertainty, and we like to be able to control it in our lives usually, right, and minimize it. And, you know, one of the things that I've gotten to work on, and that was actually a focus of my PhD, was how do you minimize that quantum uncertainty to improve certain precision measurement devices? Like, you know, clocks. As in like measuring time more precisely? Exactly. Monica figured out a way to make atomic clocks even better, a clock that beat previously known limits of precision. Wow, okay. Fancy. My kind of scientist. How did she do it? So to fully appreciate what she did, I want to explain this key

concept in quantum mechanics called entanglement. All right. Remember I told you to bring a coin to this recording session. Yeah, my closet coin that's always here. Are you a magician? Yeah. Okay, here we go. I have my coin too. We're going to pretend that these coins are particles.

Okay. We're going to toss the coins in the air at the same time, and I want you to tell me if it's heads or tails. Okay. All right. Here we go. Three, two, one. Okay.

Tails, baby. I got tails too. Now, your coin landing on tails. has nothing to do with my coin landing on tails, right? That's how coins work. That's true. But what's amazing is that at the quantum level, we could have a situation where every time you get tails, I get heads.

Like every time? Every time. So if we tossed 50 coins, you would get tails each time and I would get heads. Okay. So what does this mean, Kwong? Right. So the next part's a little tricky. And there are limits to our coin metaphor.

Remember, the coins are supposed to be particles. But what it means is that at some point in our particles history, they developed some kind of relationship to each other. Did a little dance, exchanged some information. It's not essential that they're in the same location, actually, for this to happen. But the point is they then moved apart where you and I are flipping them now. And our tosses look random, but they're not because there's some connection between them. from like this hidden relationship that they have.

Yeah, the fate of the coins have been tied together, even when they're in different locations, they continue to share that connection. And that phenomenon is called entanglement, sort of these correlations within the randomness. And what it tells us is that there's information that I don't have and that you don't have, but it's somehow shared between us.

And right, so that information in principle can be like completely non-local. It doesn't exist here or there. It's distributed in this non-local way. This is deep, dude. Right? And Monica studies how particles interact in this entanglement state, using lasers to cool atoms, slowing them down so much that she and her colleagues can control their motion and position and take pictures of how they interact. Okay, so why does she want to create this entanglement state specifically? Well, because if you can figure out the entanglement of a group of particles, say that tails on one coin, so to speak, will mean heads on the other.

I'm kind of oversimplifying. But if you can figure that out, you can reduce the uncertainty that governs their behavior. Figuring out their relationship, you can find order within the randomness. You sort of squeeze down those quantum fluctuations, that quantum uncertainty. And reducing that uncertainty is really useful for precision measurements, like that. like an atomic clock. And this is exactly what Monica did for her PhD, demonstrating the very first atomic clock that harnessed the properties of entanglement. She and her colleagues' clock was three times more precise than a clock operating at the standard quantum limit. Three times more

precise. You get it? Yes. It's time. It's clock. Wow. Nice pun. Thank you. Now, it's been a decade since that paper on atomic clocks was published. Monica has her own lab at Stanford and is working on other things. But this technique that she demonstrated back in grad school is out there in the world. I'm sort of happy to let other people take the technique and run with it and push it towards improving

those best clocks. And then you can ask sort of where will we see the impact of those? We see atomic clocks in navigation on GPS satellites. Now, Monica's lab is not exploring the application. of quantum mechanics? What they're doing is they're building tools and running experiments to expand our understanding of quantum mechanics. And not in this Marvel movie, Ant Man, you know, you push a button and it's so easy kind of way. So we're like troubleshooting constantly,

these incredibly complex tools. And Monica loves that part, tinkering and figuring out seemingly unsolvable problems. You know, I certainly am an optimist. If something sounds like an exciting goal and I don't see a reason why it's impossible, then I'm eager to give it a try. So yeah, I think being an optimist certainly helps me. And what also helps me is having other people to work with, be that, you know, colleagues or students in my group who are less optimistic and ask the challenging questions about, you know, what have you thought about this? I'm going to tell you what, Kwong, grad students make the world go around. I'll say it. That they do. And Monica, there's so much she wants to do in her lab with her students, she hasn't quite decided how she wants to spend

this award money. There are so many things I'm excited to do and so little time. So I really wish there were some way to just sort of buy time, which is not possible. But to the extent that, you know, I keep wondering, is there some way to sort of make my time go further? Which is a classic problem that not even quantum physics can solve. So true. So true. All right, Kwong, thank you so much for introducing us to Monica, certified genius. She truly is, and you're welcome. To see the work of other MacArthur fellows, we've linked their profiles in our show notes. This episode was produced by Britt Hansen, edited by Viet Le with help from Jeff Grumfield, and fact-checked by Arella Zabidi. I'm Emily Kwong. And I'm Maddie Safaya. Thanks for listening to Shortwave

for Menfield.