Katherine Forrest: Right, so if you're listening to this and you don't get your full explanation of everything you need to know about quantum computing, just hold on to your britches. We're going to get there.
Anna Gressel: But tell us what you find interesting and what you want to hear about on future episodes.
Katherine Forrest: Yeah, yeah, let's get some audience feedback, Anna. Let's get some audience feedback on some of this, right? So I want to start at the beginning, which requires us to talk a little bit about another sort of PTSD-type phrase called quantum physics. And as Anna knows, but the audience may not, I've had a little bit of an interest in quantum physics really for years. And it's what originally brought me into the area of artificial intelligence to begin with. So we're going to talk about quantum physics to get us into quantum computing because quantum computing does something that's different from regular computational processes that occur in your computer. So let's put AI to the side for the moment. Let's get ready to take a couple of steps, one at a time, and talk a little bit about the physics of quantum computing.
Anna Gressel: Okay, well that does in fact bring me back to drawing electrons and passing notes in physics class to my friends because I am actually old enough that we passed like physical hard-copy notes because texting was expensive at the time. So let's go back to that time, Katherine.
Katherine Forrest: Let's go back to that time. Let's go before that time because by the way, when I was young, they didn't have texting, Anna. I just want to say that it wasn't a matter of expense. It just didn't exist. All right, so there, I've dated myself. But let's all go back in time. And I want to talk about the fact that a classical computer like a laptop, the laptops that people probably are working with every day, they all use bits. 0s and 1s that actually form the gates, if you will, to the on-off switches that makes the computer do all the whizzing and whirring that creates all of the things on your screen and it allows the computational processes to function within your computer. But everything boils down to these 0s and 1s being switched on or off.
Now, a quantum computer, which by the way, you cannot go out and buy. If anybody's thinking, can I go buy a quantum computer, the answer is no. The day you can go out and buy a quantum computer, the world is going to be a very, very different place. We're talking about moving towards the quantum computer age. But a quantum computer actually operates on a totally different level and in a different way from your normal laptop. And it goes down to the smallest sort of quantum level in the physical world, and it operates on something called qubits. Now, here's the first catch: a qubit can either be an 0 or a 1 or both at the same time. Now, let me just do that again. It can be an 0 or a 1 or both at the same time. So it's about probabilities. Is it an 0? Is it a 1? When it's both at the same time, will it end up being an 0 or a 1?
Anna Gressel: It's kind of like our listeners, Katherine, who don't know if “Waking Up With AI” will be Katherine and Anna or Katherine or Anna, and they just have to wait to find out every week.
Katherine Forrest: Right, right. Wait, hold on, that's great. That's like Schrödinger's cat, only like we're not going be decayed by an atomic particle. So that's right, today you're getting both of us. We're both all, we're 0s and 1s at the same time. But, you know, in a classical computer, again, the 0s and 1s are fixed. They're on, they're off. In a quantum computer, they're not. They can be both at the same time. And so the possibilities for the computational processes that a quantum computer can undertake are astronomical because everything can be computed in parallel with all of the 0s and 1s being held as both possibilities for long periods of time. So we're going to go on to that in just a second.
Anna Gressel: Yeah, Katherine, I think it would be helpful to tell our audience why the 0s and 1s can actually be in both states of on and off at the same time. That's a good place to start.
Katherine Forrest: All right, so that goes to something that's going to be our first sort of term that we're going to learn, and that's going be called superposition. It's all actually one word, superposition. And the superposition is, sort of, the word for the qubits being able to be in both states — the on, the off, the 0, the 1 — at the same time.
Anna Gressel: Yeah, and I think flipping a coin is one of the more intuitive ways to understand that. When the coin is in the air spinning, it's not really heads or tails in any kind of particular position. It's kind of both heads and tails as it flips through the air.
Katherine Forrest: Right, exactly. And now I'm going to add in another vocabulary word called entanglement, because two qubits can be entangled, they can have a relationship to one another. And it's really very complicated, but take it this way: if you have two qubits that are entangled, then, if you know the state of one, you'll know automatically the state of the other. That somehow there is information shared between the two qubits. So if you think of like two qubit particles that can be long distances away from each other, if they're entangled, they automatically will know about the other one's state, as well as their own.
Anna Gressel: Okay, Katherine, well, I think we are going to need an example of this. Should we go to — drum roll — the cat?
Katherine Forrest: Well, you know I love the cat, okay?
Anna Gressel: I know!
Katherine Forrest: I love the cat, the cat so much that…
Anna Gressel: That's why I gave you a lead in.
Katherine Forrest: I know, I love the cat so much that when I was a federal judge, I managed to get this cat that we're going talk about into a federal opinion. So if you search me in Westlaw, Judge Forrest and cat, well, there might be more than one cat decision, I don't know, but Schrödinger’s cat, then you're going come up with how I managed to wedge it in.
But, here we go. Erwin Schrödinger developed a thought experiment in 1935 that has forever after been called Schrödinger’s cat. And here's the idea. There's this cat. You can imagine any kind of cat that you want to imagine. I'm going to pick sort of an Alice in Wonderland kind of orange and white striped cat. And it's in a box that's sealed. And the box has a radioactive atom in it that might or might not decay in a certain period of time. We just don't know. Okay, so you've got the cat, it's in the box, and this radioactive atom is sitting in the box and it might decay. Now there's a Geiger counter, which of course can measure radioactivity in that box, and it can detect radioactivity if the atom decays. And if the radioactive atom decays, the Geiger counter gets triggered. And if it's triggered, it releases a poison that would then kill the poor cat. Now, by the way, this is not a real cat. This is a thought experiment.
Anna Gressel: Well, I'm glad we don't really have a real cat we're dealing with here. There are like an awful lot of ways to die in this experiment, so. But, Katherine, should we talk a little bit more about, you know, the interesting position that this cat is in? And what does this experiment tell us about quantum physics?
Katherine Forrest: Right, right. So again, if the atom does not decay and the poison's not released then the cat lives. So in the quantum physics world, we have this atom that is in a position of being both possibly decaying and possibly not decaying. It is both at the same time. We don't know. And that's called, again, superposition. Superposition is something being in two states at the same time. You're both an 0 or a 1 or you're decaying or not decaying. That's superposition. And because that atom is in superposition in the sealed box that we're not looking at, we're not looking into, the cat could be either alive or dead. It's both alive and dead at the same time, which is really something that's hard to wrap your mind around. So we don't know the answer to it. And so what we're saying is that in quantum physics, the position of quantum particles are only fixed in one state, in one particular state, if they're observed or measured. And until they're observed or measured, the quantum particle is in every possible state.
Anna Gressel: Yeah, going back to our coin flipping example, it's almost like the coin is flipping in the air until someone decides I'm going to measure whether it's a head or a tails and then it lands. So, I mean, Katherine, I'm curious about whether you think that resonates. But why don't we talk about how that reads back or like maps back on the Schrödinger’s cat example.
Katherine Forrest: The quarter example or the coin example is, because there are no more pennies, as we know. But maybe, or soon there won't be any more pennies. Collect those pennies, folks, so you can do your own experiments. But they're at such a macro, bigger level that it doesn't actually work like that, but the concept is similar to what you're saying.
And by the way, there have been a number of experiments, a large number of experiments that have proven the concepts that we're talking about on today's episode again and again, that quantum particles can exist in different states, all states, until they are measured or observed or another way of talking about it is seen. And once they're measured or observed or seen, then we're able to say, “oh, the particle is in this position or it's in that position” because we've literally, at that point, we've measured it. And so going back to the cat example, the cat's in the box, the atom may or may not be in a state of decay, the cat may or may not be alive or dead. And so what we know from quantum physics is that, until we open the box and see what's happening inside, everything is possible. There are all kinds of realities going on inside that box, and that cat is living all of those realities at the same time. That's superposition. It's all about probabilities until there's an observation or measurement.
Anna Gressel: Yeah, so you're saying, and I think this is what that experiment says, the cat is both alive and dead all of the time until the box is open. Or another way put, until the atoms are actually measured, the qubits are actually measured and we know what state they're in.
Katherine Forrest: Or it can be both alive or dead. And it sounds sort of crazy, right? And it's, again, this is a thought experiment, but it helps illustrate that at a quantum level, things can actually occupy multiple possible states. And you can think of it as, and there are a number of physicists who do think of it this way, that there could be multiple realities. But let's put that aside. It's the act of observation that really reduces something from superposition into a different state.
Anna Gressel: Katherine, do you want to talk about one more example? Maybe we can do the double-slit experiment.
Katherine Forrest: Well, the double-slit experiment, Anna, as you know, it's another one of my favorites. And the double-slit experiment has been around for a long time. And it's actually an experiment. So before we were talking about Schrödinger’s cat and the possibilities of it being either alive or dead in the box, and we don't know if the atom is decayed or not decayed, all possibilities are there. With the double-slit experiment, these are actual experiments that are repeatable, and they have been repeated numerous, numerous times with very sophisticated equipment to try to figure out what's going on. And this is one of the mysteries of quantum physics because people aren't exactly sure why it turns out this way. But let's just talk about it for a moment. In this experiment, you've got some quantum matter, like a photon or an electron, that can behave as either or both a wave (think of like a wave in the ocean) or a particle, like a point, like a little tiny speck of sand, at the same time. It's both a wave or a particle at the same time, or you don't know which it is. And that state of being either or both continues until, again, the moment of observation or measurement.
So imagine a wall with two narrow slits that are cut in that wall, right? You've got two slits in the wall, and behind the wall is a screen. And what you're going to do is you're going stand in front of the wall, looking at the two slits, and you're going to shoot particles, these electrons or photons, at the wall. And your expectation is, this is the human expectation, based upon what we would normally have expected in classical physics, that the particle would go through one slit or the other slit and then form a band of particles that accumulate on the other side of the wall. And if it was solid particles all the time, that's what you would expect. But here is what happens. And this is sort of the extraordinary sort of mystery of quantum physics, right? Which is that when you in fact shoot the photons at the slits, they don't create the two single bands on either side that are right behind the slits, the solid bands where the particles are collecting. But instead, there are like dark wavy stripes that occur on that screen. And this is called, a third vocabulary word, an interference pattern. It's sort of like a wave-like pattern. So the particles are somehow going through the slits, but they're going through the slits in a wave-like pattern, not as a, just a particle sort of going straight through and hitting the other side. They're going through in kind of a wave way. So the particles are both particles and waves at the same time. Now here's the catch. If you place something that can measure or observe the particles just before they go through the slit, like a detector, something that can observe the little electron or photon before it goes through the slit, it actually, again, collapses from its superposition state. It goes into a particle. It becomes a particle and it chooses one slit or the other and, on the other side of the wall, because of that active measurement, you then do see that solid stripe of particles collecting. So again, if you observe the particle just before it goes through the slit, it doesn't act like a wave. It actually acts like a particle. It goes through the slit and creates a solid band of particles on the other side, and you don't get that wave-like interference pattern. So in other words, the fact of observation, just like Schrödinger’s cat and opening up the box, the fact of observation or measurement reduces the probability of something, of this now, the particle being one thing or another into something definite.
So with quantum computers, Anna, we're getting back to it now, okay? We've gone through our two experiments. We're going to get back to quantum computers. Quantum computers are actually using these principles of superposition, of things being two things or both things at the same time, of things having a possibility of being in more than one state at the same time to do massive amounts of parallel computation.
Anna Gressel: Katherine, that is completely fascinating, and I think it is really interesting. We promised a definition, so I'm going to give everyone NIST's definition of quantum computing or quantum information science, which is pretty consistent with what you were talking about. It says, “quantum information science involves using the smallest bits of matter and energy —electrons inside an atom, tiny circuits, massless particles of light — to store, carry and process information.” And as we know, those smallest bits of matter and energy are governed by exactly what you're talking about, quantum mechanics. And what that definition is including at the end when it says both governed by quantum mechanics, is that the bits can be both in the 0 and 1 state every time. So we're talking again about the qubits here. And computations can occur anticipating basically every possible combinations of 0s and 1s. And so that's like the real power of quantum computing. We'll talk a lot more about what that means in practice, but just wanted to relate that definition back to the fundamental physics underlying it.
Katherine Forrest: Right, terrific, and I think that's all we've got time for today. But the takeaway is that quantum computing has a massively powerful computational ability. And we're going to talk about why it's so hard to make a quantum computer and all of the advances in quantum computers and how quantum computing does relate to artificial intelligence and potentially incredible advances in AI in our next episodes, in a couple of episodes coming up, Anna. So that's it.
Anna Gressel: Yeah. All right. Well, can't wait to talk more about quantum algorithms.
Katherine Forrest: Are you traumatized? Are you traumatized? Are you traumatized?
Anna Gressel: Certainly not. Not me, but our audience, let us know if you're traumatized and you just want to be back in AI land. But otherwise, we're going to knit together what are some of the most important advances that really do bear upon each other. And quantum computing is a really fundamental part of, I think, some long-term roadmaps and promises of AI. So we'll get back to that. For now, we're signing off. Tell us if you want a “Waking Up With AI” mug. Email us. And otherwise, have a great start to your spring, and we'll see you guys next week.
