TechStuff Tidbits: What the Heck is a Qubit?

totally wrong. That's Cubert. A cubit is something else entirely, I know cringe jokes. Also, Originally I thought maybe I would go a different way with that, and I would talk about cubits being a unit of measurement used to build arcs in Biblical times. But you see that joke about what a cubit is, Well, it existed in two states simultaneously, but ultimately, when it came time for me to choose which joke to use, it had to collapse into a single state, which is the Cubert joke. And

that whole bit about collapsing into a single state. I can't promise it'll make more sense later. But I can promise we're gonna talk about it all right. So to understand what a cubit is. Cubit, by the way, actually stands for quantum bit. Well, it stands to reason that first we have to understand what a bit is. Now. Way back in nineteen forty eight, in the early days of computer science, a man named Claude Shannon published a

work titled A Mathematical Theory of Communication. Shannon was mentored by a guy named Van Var Bush that I really need to dedicate at least one episode, but probably multiple episodes two at some point, very important person in tech in general played a large part in some really historic and sometimes terrible technological events in history. I have actually dedicated an episode to Claude Shannon in the past, so if you go and do a search in the Tech

Stuff archives, you'll find an episode just about him. But anyway, in this work, Shannon proposed a basic unit of information, a binary digit or bit. The bit exists in one of two states. It is either a zero or a one.

Shannon's work goes into a lot of other territory with a fascinating treatment on communication theory that fundamentally changed how communication engineers think about the subject, but it gets really technical really quickly, and I honestly would have to study it for days to feel comfortable even talking about it in a way where I didn't feel I was getting

it all wrong. So rather than blindly lead you into a discussion that I would likely get completely wrong, we're going to move on to something else that's equally complicated. But for our discussion, the important thing is the bit zero or one. You can think of it as no or yes, or off or on. It's as basic as you can get. By grouping bits together, you can express more complex information. So one bit has two states. If

you have two bits, you have four states. You can express zero, zero, zero, one, one, zero, and one one. With three bits, you've got eight possible states. Four bits, you've got sixteen possible states. By the time you get up to eight bits, it's two hundred and fifty six states. So you see how adding one bit to a string doubles the number of states that string can express compared

to when it was one bit fewer. All right, So then we get into an era in which computer scientists start working with this concept in a practical way, and after a while, computer scientists begin to agree on other stuff, like the idea of eight bits representing a bite. This wasn't always the case. There were some who proposed six bits rather than eight, et cetera. But we're gonna skip

way ahead and talk about processors for a moment. Processors take data in the form of bits and execute operations on that data to create output, like mathematical operations, and those operations come from a program. The program is really just a set of instructions that the processor is meant to follow while working with this data, and it generates some sort of result. And a lot of factors determine how fast the processor is, like how much data it

can process within a given amount of time. Now, generally speaking, the more bits the processor can accept at once, and the higher the clock speed of the processor, which really means the number of operational steps the processor can complete

in a second. Well, then the more powerful the computer is and the faster it will solve problems to a point, but there are some computational problems that are much harder to solve than others, and even a fast processor can get bogged down by them and it becomes impractical or even impossible to compute that problem. So, for example, there's the famous traveling salesman problem, which is a type of NP hard computational problem. The NP stands for nondeterministic polynomial time.

But we don't need to really get into all of that. The traveling salesman problem presents a list of cities and it asks the question, what is the shortest route starting from the salesman home city to each of these cities and then back to home without visiting a city twice.

What's the shortest route that you can take? Well, for a computer to solve that question, it would need to calculate the route using every possible combination, and that route obviously gets more complicated as you add more cities to the list, and a sufficiently large list would keep a computer busy for a really long time, like months or years, or decades or centuries, depending on the complexity of the problem. So that's an issue, right. You cannot easily solve this

class of computational problems with a classical computer. But what if you could design a computer that could potentially solve this problem in a flash by essentially calculating every route simultaneously. Now we're getting into the possibilities offered up by quantum computing and the cubit. The cubit is a quantum bit, and like a bit, it can have a value of zero or one, though we represent them asket zero and

cut one states. But I'm gonna leave it there because describing representation and notation in an audio only podcast is futile. I'd be like, okay, then you have a little squiggly line. None of that would make any sense, so we're gonna leave it there for now. But here's the thing. A cubit can also have both values at the same time and technically all values in between, and hold those values in superposition until the system collapses and the cubit assumes

one or the other states. And which one it assumes is based on probabilities. So it may be that it's a fifty to fifty, which means half the time the cubit would be a zero and half the time the

cubit would be a one. It doesn't have to be fifty to fifty, however, so this is one of those weird quantum effects that Schrodinger wanted to poke at with his cat thought experiment see Early quantum physicists theorized about superposition that certain quantum stuff can hold multiple states simultaneously until something disturbs them, at which point they collapse into

a single state. Schrodingsher's absurd example was that of a box containing a kitty cat and then a time release method of making the kitty cat unalive, as you might say on TikTok. But this time release method would be unpredictable. It might trigger five minutes in or it might hold off for hours. So you've got this box, thirty minutes have passed. Is the cat alive or dead? Well, if we were to think of the cat as being in a quantum state, you could argue the cat is both

alive and dead at the same time. And it's only when you open the box and observe the system do the possibilities collapse into one reality. And in this reality we're gonna say the kitty cat lives. Because I've always hated this thought experiment, Shrodinger was trying to say this idea was ridiculous, And of course, on the classical level of cats and cars and cigar boxes and stuff like that, all the stuff we can see and touch and manipulate, it is absurd. But at the quantum level, it holds

true quantum effects can exist in two states simultaneously. It's wild,

but it is true. So if you could harness something that works on the quantum level, like electrons, for example, and you could use some feature of electrons such as their spin where they spin up or spin down, you could use that to serve as a cubit, And in a properly isolated system, you could use a bunch of cubits to run algorithms specifically designed for quantum systems, and these cubits, by occupying all states simultaneously, could generate all

possible outcomes in the time it would take to solve you know, the hardest one. Another way to think about it is that if you have a bite, that is eight bits that are strung together, you can have one of two hundred and fifty six values. If you have eight q bits, then you can have all two hundred and fifty six values at the same time, at least until you measure it, at which point it loses coherence and settles into a single value and becomes one of

the two hundred and fifty six possibilities. But while in superposition it's all of them. However, it gets weirder, and I'll explain after we come back from this quick break. Okay, what could be weirder than superposition? Well, I haven't talked about entanglement yet. All right. For this explanation, let's imagine that we have two cubits, and we'll say our cubits are in the form of electrons and their direction of spin,

so the electrons can spin either up or down. And let's say I've prepared the cubits so that right now they're both spinning down, and we'll call that the zero state versus the one state for this example, So both cubits are spinning in the zero state, cubit A and cubit B. Now, if I apply an oscillating magnetic field to cubita a magnetic field at a frequency proportional to the energy difference between cubit a's zero state and its one state, I can actually rotate cubit A. I can

rotate its spin. And the presence of cubit B complicates things a little bit, because these two cubits create their own magnetic fields. I have to take into account cubitb's magnetic field as I apply this external magnetic field to rotate cubit A. But I can do that and then move Cubita into superpositions. So now Cubita is both zero and one at the same time. All right, Now let's move on to cubit B. Now, remember I started with

both cubits in the zero state. They're both spinning down. Well, now I apply the magnetic field I would need to use to rotate cubit B if Cubita were still in the zero state, except Cubita isn't in the zero state anymore. Or rather it is, but it's also in the one state because I've put Cubita into superposition. Well, now, when Cubita is in zero, cubit B will rotate to one

because of this oscillating field I've put on it. But when cubit A is in the one position, cubit B will stay in the zero state because I would have needed to use a different frequency in my magnetic field to make cubit be rotate if Cubita is in the one state, so cubb also goes into superposition. If Cubita is zero, then the rotation worked, and if cubit B is one, then the rotation didn't work. But Cubita is technically both, so the rotation both did and didn't work

at the same time. The two cubits are entangled, and the state of one depends upon the state of the other, and they're opposite. Even if we were to separate these two cubits and we were to put them at either end of the universe, they would remain entangled as until we observed them or something else disturbed them, at which point we would lose coherence and the state becomes either zero or one, and the state of the other one would be the opposite of the one you observed, even

if it's on the other side of the universe. So if you went to one end of the universe and someone went to the other end of the universe with the other one, you've got Cubita, they've got cubit B. You observe Cubana, you see that it's zero. You know that cubit B was a one crazy, even though they were all the way across the universe from each other.

Einstein hated this. By the way, he couldn't get the math to prove that it didn't work, but he hated the idea, and he called it spook key action at a distance in quantum computing entanglement creates a really counterintuitive opportunity. You can code for two bits that have unknown but opposite states, Like you don't know if cubita is a zero or a one, but you do know that whatever it is, cubit b is the opposite. And that might not sound useful at the surface level, but it opens

up opportunities that simply aren't possible with classic computers. So, for a subset of computational problems, the ones that are really hard for classic computers, a quantum computer with sufficient cubits and the right algorithm you need both can turn what would be a massive challenge into a metaphorical piece

of k Now. For other computational problems, a quantum computer would be no better than a classic computer, and depending on the number of cubits the quantum computer has at its disposal, it might be equivalent to a really, really bad classical computer. The thing is, some interesting and potentially dangerous problems might be simple for a quantum computer to unravel,

problems like classic encryption techniques. So a typical approach to encryption involves using mathematical operations and a really large number to scramble a message. Only someone with the proper key, can reverse this process to get the unscrambled message and to guess the value of the key that unscrambles everything would take a really, really long time. How long depends upon the strength of the encryption, but if we're talking

like military grade, you could be there forever. But with a quantum computer that has a lot of cubits and the right algorithm, you could potentially solve for the encryption key in just a few minutes. This is why quantum computers could spell the end of our current methods of encryption. A person with access to a sufficiently powerful quantum computer and that pesky algorithm would then hold the skeleton keys that fit all the digital encrypt locks that are out there,

which is kind of spooky. And for that reason, researchers are working on quantum encryption methods that can stand up to quantum computers that you know, uses a different approach to scramble those messages so that they stay safe from

all but the intended recipient. Also, I started talking about Claude Shannon as the guy who popularized the term bits, although Shannon himself gave credit to John Tukey, whom Shannon said, use the term bits in a memo, but Shannon's is the first earliest you know, published work to use the term bits. But who coined cubit, Well, that would be Benjamin Schumacher, who submitted an article titled quantum Coding in nineteen ninety three to Physical Review. The article actually published

in nineteen ninety five. Schumacher is a theoretical physicist. By that, I mean he's a real physicist. He's not theoretical, but he works in theoretical fields, including quantum information theory. He did for quantum information theory what Shannon did for communications theory, with about half a century separating the two, which is pretty darn cool. And so that's the basics on cubits. And if you were to come up to me and say do you understand this? Do you understand why it happens?

I would honestly tell you no. But then when we get down to quantum effects, that's just the truthful answer for everybody. We can say that definitely happens, that we have the experimentational evidence to show that this does happen. Why it happens, that's a question that we're still trying to answer, and maybe we'll never come up with it, but it's really cool to look into it. Now, if you'll excuse me, I have a game of Hubert to

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