WEBVTT - Quantum Computing 101 0:00:04.160 --> 0:00:07.160 Get in touch with technology with tech Stuff from how 0:00:07.240 --> 0:00:14.120 stuff Works dot com. Hey there, and welcome to tech Stuff. 0:00:14.240 --> 0:00:18.800 I am Jonathan Strickland, the host, an executive producer with 0:00:18.840 --> 0:00:22.480 How Stuff Works and a lover of all things tech. 0:00:23.040 --> 0:00:26.960 And this is another episode in the little mini series. 0:00:27.000 --> 0:00:30.560 I'm recording while I'm attending the Think two thousand eighteen 0:00:30.600 --> 0:00:34.800 conference in Las Vegas, Nevada. It's sponsored by IBM, and 0:00:35.240 --> 0:00:39.640 IBM does this big conference. It's sort of a an amalgamation, 0:00:39.800 --> 0:00:44.720 a gloming on to several different smaller conferences that IBM 0:00:44.800 --> 0:00:48.360 has been holding for several years. They kind of pushed 0:00:48.360 --> 0:00:51.280 them all together and turned it into a giant, mega conference. 0:00:52.080 --> 0:00:54.320 And I emphasized giant. I mean there are tens of 0:00:54.320 --> 0:00:57.600 thousands of people attending this conference. It feels like more 0:00:57.680 --> 0:00:59.959 than that when you're trying to get through the Mandalay 0:01:00.120 --> 0:01:05.440 Bay Conference Center, because holy cats, lots of executives, a 0:01:05.520 --> 0:01:08.600 lot of blazers, a lot of blazers out there, folks. 0:01:09.000 --> 0:01:11.600 I gotta watch my what I say because pretty much 0:01:11.640 --> 0:01:16.280 everybody in there is a giant stakeholder in some big 0:01:16.319 --> 0:01:19.319 business or another. And chances are if I if I 0:01:19.360 --> 0:01:22.479 say something rude, I've just insulted a millionaire, and I'm 0:01:22.520 --> 0:01:25.360 not in that tax bracket. But let's talk a little 0:01:25.360 --> 0:01:28.440 bit about one of the topics that got a lot 0:01:29.319 --> 0:01:33.360 of coverage here at IBM think two thousand and eighteen, 0:01:33.400 --> 0:01:37.840 and that is quantum computing. It's a big deal, and 0:01:37.880 --> 0:01:41.040 that's because quantum computers are beginning to emerge from the 0:01:41.080 --> 0:01:45.800 realm of experimental science into practical applications. In fact, you 0:01:45.800 --> 0:01:48.200 could argue it's already there and has been for a 0:01:48.240 --> 0:01:51.240 couple of years, but it's still relatively new and I 0:01:51.240 --> 0:01:53.680 think very mysterious for a lot of people. And I've 0:01:53.680 --> 0:01:56.280 talked about a little bit in previous episodes, but I 0:01:56.320 --> 0:01:59.480 really wanted to dedicate a an entire episode kind of 0:01:59.560 --> 0:02:04.960 quantum computing one oh one and really talk about the 0:02:05.000 --> 0:02:09.119 principles behind it, the history behind it, what it might 0:02:09.160 --> 0:02:12.280 be used for, why it's such a big deal in 0:02:12.280 --> 0:02:15.080 the first place. So this is our full episode on 0:02:15.080 --> 0:02:17.400 the topic, and I'm going to reference some of the 0:02:17.440 --> 0:02:21.080 things I've learned while I've been at this conference. Let's 0:02:21.160 --> 0:02:23.800 do what I love to do. This is like a 0:02:23.840 --> 0:02:26.240 good old traditional episode of tech stuff. We're gonna dive 0:02:26.280 --> 0:02:30.320 into the history of quantum computing and quantum mechanics and 0:02:30.400 --> 0:02:33.520 quantum theory. So this all begins before the computer age. 0:02:34.400 --> 0:02:37.840 We have to discuss the history of quantum mechanics itself. Now, 0:02:38.600 --> 0:02:42.120 I'm not going to go into exhaustive detail, because to 0:02:42.200 --> 0:02:46.760 do that would require an entire podcast series, not just 0:02:46.800 --> 0:02:49.960 an episode, but a series of episodes to kind of 0:02:49.960 --> 0:02:53.720 talk about all of the developments in quantum mechanics. And 0:02:53.720 --> 0:02:56.919 not only that, but it's a messy history filled with 0:02:57.360 --> 0:03:01.760 a lot of scientific debate and our humans and uh 0:03:02.120 --> 0:03:07.440 experiments and counter experiments, thought experiments, aim calling. There was 0:03:07.480 --> 0:03:10.919 some adultery in there too. I mean, it's it reads 0:03:10.919 --> 0:03:13.839 like a soap opera at times, and and like I said, 0:03:13.840 --> 0:03:18.000 it's just it's so deep and dense that to really 0:03:18.120 --> 0:03:21.600 cover it would require multiple episodes. So this is kind 0:03:21.600 --> 0:03:25.120 of like a an introductory a bird's eye view of 0:03:25.160 --> 0:03:28.600 the history of quantum mechanics. So let's talk about the 0:03:28.639 --> 0:03:33.000 developments around the turn of the last century, the twentieth century. 0:03:33.040 --> 0:03:36.080 In nineteen hundred, it only been a couple of years 0:03:36.080 --> 0:03:38.920 and scientists had even discovered the existence of electrons at 0:03:38.920 --> 0:03:42.160 that point. No one was even sure in nineteen hundred 0:03:42.480 --> 0:03:46.480 if electrons were even part of the atom. They didn't 0:03:46.480 --> 0:03:50.320 know our electrons actually a component of atoms or are 0:03:50.360 --> 0:03:52.880 they something else? So do they coexist with atoms but 0:03:52.920 --> 0:03:56.280 they're not bound to atoms? They weren't sure. In nine hundred, 0:03:56.760 --> 0:04:00.200 there was general agreement that atoms were in fact a 0:04:00.320 --> 0:04:04.280 kind of a fundamental particle, but beyond that, there wasn't 0:04:04.320 --> 0:04:07.960 a whole lot of agreement on them. No one was 0:04:08.000 --> 0:04:11.680 really sure what made the atoms of one element different 0:04:11.760 --> 0:04:15.040 from another, and therefore they weren't sure why elements were 0:04:15.080 --> 0:04:17.920 different in the first place. They could identify elements, they 0:04:17.920 --> 0:04:22.800 could identify the qualities of elements, but they couldn't explain 0:04:22.920 --> 0:04:27.000 why they were different from each other. Well, in there 0:04:27.080 --> 0:04:30.640 was a smarty pants physicist, Max Planck, who was trying 0:04:30.640 --> 0:04:34.800 to work out some reasons behind a curious observation that 0:04:34.839 --> 0:04:38.599 people had noticed for centuries but didn't They couldn't explain it. 0:04:38.920 --> 0:04:41.960 And that was the nature of heat radiation and the 0:04:42.080 --> 0:04:45.560 light that it can produce. So let's say that you're 0:04:45.560 --> 0:04:48.960 a blacksmith and you've got some iron, and you put 0:04:49.080 --> 0:04:51.719 in the forge and you heat the forge up. Eventually 0:04:51.760 --> 0:04:54.560 that iron, as it grows hot, will begin to glow, 0:04:55.000 --> 0:04:57.479 and it first will kind of glow red, and then 0:04:57.480 --> 0:04:59.599 that red will get brighter and brighter, kind of turned 0:04:59.600 --> 0:05:02.159 into an orange. And if it gets hot enough, it'll 0:05:02.320 --> 0:05:05.600 glow white. If you could get it hot enough before 0:05:05.600 --> 0:05:08.720 it melted, you could make it even glow blue. These 0:05:08.760 --> 0:05:12.680 different colors would represent different energy states, but no one 0:05:12.720 --> 0:05:14.640 knew that at the time. No one was able to 0:05:14.680 --> 0:05:19.960 explain why iron would change color as it got hotter. 0:05:20.880 --> 0:05:23.000 So Plank was working on this problem. He was trying 0:05:23.040 --> 0:05:25.359 to figure out, well, what is what explains us, or 0:05:25.400 --> 0:05:28.719 what at least describes this, and eventually came up with 0:05:28.760 --> 0:05:33.159 a formula that fit the observations he made in experiments. 0:05:33.720 --> 0:05:37.720 He had figured out a formula that that seemed to fit, 0:05:37.880 --> 0:05:41.760 But why did it fit? Why did that formula describe 0:05:41.800 --> 0:05:44.800 what was happening? He couldn't tell. He wasn't sure, No 0:05:44.839 --> 0:05:47.320 one was sure at first. He kept working on it, 0:05:47.560 --> 0:05:51.840 so eventually Plank figured out that the atoms could apparently 0:05:52.040 --> 0:05:56.640 only take on certain quantities of energy, So it could 0:05:56.680 --> 0:06:00.480 take a certain amount of energy, and then any above 0:06:00.520 --> 0:06:03.240 that it could not accept until it got to the 0:06:03.279 --> 0:06:07.279 next specific allowable energy level. So you could think of 0:06:07.279 --> 0:06:11.679 it as steps of energy. You could accept a certain amount, 0:06:12.560 --> 0:06:16.520 and then you could step up and accept a new 0:06:16.760 --> 0:06:20.760 larger amount, but anything in between those two steps didn't 0:06:21.040 --> 0:06:24.520 fit the formula. And this was very curious. It wasn't 0:06:24.560 --> 0:06:28.240 something that was continuous, right, This idea of steps of 0:06:28.360 --> 0:06:34.040 energy levels was really perplexing at the time. You might 0:06:34.120 --> 0:06:38.200 think of it more like a continuous string, but it wasn't. 0:06:38.440 --> 0:06:42.279 It was this broken series of steps. So this really 0:06:42.320 --> 0:06:45.120 got people wondering what the heck was going on. Um, 0:06:45.440 --> 0:06:49.280 how could materials take on specific increments of energy rather 0:06:49.360 --> 0:06:52.880 than any arbitrary amount. Planck didn't know. He didn't know 0:06:53.000 --> 0:06:55.600 why it was happening. He only knew that it was 0:06:55.839 --> 0:07:00.159 happening based upon his observations, and that the explanation he 0:07:00.240 --> 0:07:04.279 had fit what he observed. He just couldn't explain why 0:07:04.360 --> 0:07:09.200 it worked. He announced his findings on December four, nineteen hundred. 0:07:09.240 --> 0:07:11.560 Now some people trace that as the origin of the 0:07:11.600 --> 0:07:15.320 study of quantum mechanics, though of course at that time 0:07:15.360 --> 0:07:19.960 it wasn't yet called quantum mechanics. It did, however, formulate 0:07:20.000 --> 0:07:23.560 the foundation of what some would refer to as old 0:07:23.800 --> 0:07:28.840 quantum theory. Now that theory stated that these acceptable energy 0:07:28.920 --> 0:07:34.560 increments were specific quantities, right quantities of energy, and that 0:07:34.640 --> 0:07:38.480 any phenomena that would only accept certain values of a 0:07:38.520 --> 0:07:43.440 physical quantity fell into this category, and it typically was 0:07:43.520 --> 0:07:48.400 stuff on the atomic scale, tiny tiny scale, not classical scale, 0:07:48.800 --> 0:07:52.120 which seemed to follow the rules of classical physics. These 0:07:52.160 --> 0:07:54.840 things didn't seem to follow the rules of classical physics. 0:07:54.880 --> 0:07:58.280 The rules were different for some reason. So scientists said 0:07:58.280 --> 0:08:03.800 that the values of this physical quantity of energy, uh, 0:08:04.240 --> 0:08:08.000 we're said to be quantized. That's the values of this 0:08:08.120 --> 0:08:11.200 energy is quantized. It was generally believed that you'd have 0:08:11.240 --> 0:08:14.480 to do lots of experiments and make lots of observations 0:08:14.520 --> 0:08:17.880 to kind of suss out the rules for that quantization 0:08:18.600 --> 0:08:21.280 or perhaps even uncover a set of universal rules that 0:08:21.320 --> 0:08:25.480 would work in all situations. So there were scientists like 0:08:25.720 --> 0:08:29.080 Albert Einstein who seized on this notion, and they began 0:08:29.120 --> 0:08:32.640 to apply this idea to other areas of study. He, 0:08:33.160 --> 0:08:36.480 for example, Einstein, that is, proposed that the total energy 0:08:36.559 --> 0:08:40.360 of a beam of light was quantized. Several other big 0:08:40.400 --> 0:08:43.480 thinkers were looking into similar fields. But then the First 0:08:43.520 --> 0:08:48.760 World War broke out and that really slowed down progress 0:08:48.960 --> 0:08:52.240 in the sciences because a lot of the leading scientists 0:08:52.280 --> 0:08:55.400 at the time we're all in Europe, so obviously Europe 0:08:55.400 --> 0:08:59.320 being heavily affected by World War One meant that a 0:08:59.400 --> 0:09:02.160 lot of that work was put on hold. However, at 0:09:02.160 --> 0:09:05.920 the war's conclusion, things picked up again at that stage 0:09:06.000 --> 0:09:09.200 after World War One, but before World War Two, you 0:09:09.280 --> 0:09:13.680 had scientists like Max Bourne and Werner Heisenberg who were 0:09:14.160 --> 0:09:19.959 extending our understanding of the quantized world. Now Born and Heisenberg, 0:09:20.160 --> 0:09:26.880 along with Pascal Jordan's, wrote an extremely complicated but consistent 0:09:27.320 --> 0:09:33.800 theory of quantum mechanics. Meanwhile, you had another smarty pants 0:09:33.880 --> 0:09:38.160 Irwin Schrodinger or Irvin if you prefer, that would be 0:09:38.200 --> 0:09:41.760 of Schrodinger's cat fame. He was working on his own 0:09:41.880 --> 0:09:46.440 theory to describe quantum mechanics, and for a while, those 0:09:46.480 --> 0:09:49.240 two theories were the focus of a pretty nasty war 0:09:49.760 --> 0:09:53.600 within physics in which both sides were kind of disparaging 0:09:53.640 --> 0:09:58.000 the ideas of the other side. And essentially one group 0:09:58.040 --> 0:10:01.120 is saying, you guys are full of it. My theory 0:10:01.360 --> 0:10:04.440 describes what's actually happening Here's is a mess, and the 0:10:04.440 --> 0:10:09.120 other side saying, nah, our theory is far more descriptive 0:10:09.200 --> 0:10:12.199 of what is actually going on your theory is nonsensical. 0:10:12.720 --> 0:10:18.160 But then in Schrodinger and Carl Eckert, who was working 0:10:18.200 --> 0:10:24.480 completely independently of Schrodinger, both proved that these two seemingly 0:10:24.720 --> 0:10:28.320 different approaches were actually describing the same thing. They were 0:10:28.360 --> 0:10:32.000 just doing it from completely different points of reference. So 0:10:32.880 --> 0:10:35.679 on the surface they superficially seemed like they were at 0:10:35.679 --> 0:10:39.040 odds with one another, but underneath that it turned out 0:10:39.080 --> 0:10:42.400 they were. They were in alignment. As one book I 0:10:42.520 --> 0:10:46.120 read on the subject said, it's like comparing how you 0:10:46.160 --> 0:10:50.160 add Arabic numerals to how you add Roman numerals. The 0:10:50.200 --> 0:10:53.360 two processes look very different from each other, but if 0:10:53.360 --> 0:10:56.640 you do them each correctly for the same two values, 0:10:56.840 --> 0:10:59.800 you'll always arrive at the same answer, no matter what 0:11:00.200 --> 0:11:03.040 method you use. Now that's not to say that everything 0:11:03.080 --> 0:11:06.720 was smooth sailing from that point forward. Many scientists had 0:11:06.800 --> 0:11:11.400 problems with aspects of quantum mechanics, such as it's probabilistic nature. 0:11:11.559 --> 0:11:15.640 That is, much of quantum mechanics concerns itself with probabilities 0:11:15.920 --> 0:11:19.200 rather than certainties. In fact, lots of things and quantum 0:11:19.200 --> 0:11:23.839 mechanics become inherently uncertain the more you try and nail 0:11:23.880 --> 0:11:28.160 it down, the more uncertain other elements will become. That's 0:11:28.200 --> 0:11:33.160 partly what Heisenberg's uncertainty principle states. Heisenberg was specifically talking 0:11:33.200 --> 0:11:38.520 about a quantum particles position versus its momentum. Heisenberg stated 0:11:38.559 --> 0:11:41.920 that the more precisely you measure one of those two values, 0:11:42.120 --> 0:11:45.240 the less you can know about the other one. So 0:11:45.400 --> 0:11:50.679 if you measure a quantum particles position with great precision, 0:11:51.040 --> 0:11:54.679 you won't know very much about its momentum, and vice versa. 0:11:54.760 --> 0:11:57.760 And that this is just a fundamental feature of our universe, 0:11:58.000 --> 0:12:01.920 so it's tough if you don't like it. The probabilistic 0:12:01.960 --> 0:12:05.679 side of a quantum mechanics is tied also to measurement. 0:12:06.160 --> 0:12:09.000 This was a central focus of a debate between two 0:12:09.000 --> 0:12:13.480 great physicists, Neil's Bore and of course Albert Einstein. Einstein 0:12:13.600 --> 0:12:17.040 was not keen on the probabilistic nature of quantum theory. 0:12:17.600 --> 0:12:22.200 Uh He has often been attributed the phrase God does 0:12:22.240 --> 0:12:25.000 not play dice with the universe, although that is a 0:12:25.040 --> 0:12:28.120 paraphrasing of what he said. And then Niel's Bore was 0:12:28.160 --> 0:12:32.640 paraphrases saying God doesn't care what you think he's doing. 0:12:33.400 --> 0:12:35.680 Um so that was kind of the back and forth. 0:12:35.720 --> 0:12:38.800 Although both of those statements were paraphrase, neither of those 0:12:38.840 --> 0:12:41.840 were actually what the scientists were saying, just kind of 0:12:41.920 --> 0:12:46.080 was a an interpretation of what they said. Quantum mechanics 0:12:46.120 --> 0:12:51.000 experiments wouldn't really produce a definite solution. So we're used 0:12:51.040 --> 0:12:54.360 to things like calculations coming up with a specific answer. 0:12:54.440 --> 0:12:58.200 Right even let's just take simple arithmetic. If you say 0:12:58.200 --> 0:13:02.079 two plus two equals for then you know you realize that, 0:13:02.160 --> 0:13:03.880 all right, well, that that makes sense to pless two 0:13:03.880 --> 0:13:06.320 equals for that's a that's a certain value. It's a 0:13:06.360 --> 0:13:11.120 definite answer. Whereas with quantum mechanics you would get results 0:13:11.160 --> 0:13:14.400 that would be listed in terms of probabilities, not in 0:13:14.600 --> 0:13:18.240 terms of here is the answer. You would get a 0:13:18.280 --> 0:13:23.679 probabilistic distribution of possible values. So that means every single 0:13:23.760 --> 0:13:27.120 value you would get would get assigned a probability, and 0:13:27.200 --> 0:13:29.720 if you were to measure a quantum state, that would 0:13:29.720 --> 0:13:32.520 actually cause it to collapse into one of those probable 0:13:32.640 --> 0:13:38.040 values that it possibly could have been. This is also 0:13:38.200 --> 0:13:42.760 related to that concept of quantum tunneling I mentioned earlier 0:13:42.800 --> 0:13:47.079 this week. The idea of an electron could potentially inhabit 0:13:47.200 --> 0:13:51.319 one of any positions that are within a certain field, 0:13:51.840 --> 0:13:54.840 and because there's that probability, it means that sometimes the 0:13:54.840 --> 0:13:58.319 electron will inhabit that position. And if that position happens 0:13:58.360 --> 0:14:00.360 to be on the other side of a barrier, just 0:14:00.400 --> 0:14:04.120 because the zone the electron could exist in happens to 0:14:04.160 --> 0:14:07.280 overlap that barrier, then that means sometimes the electron is 0:14:07.360 --> 0:14:08.920 on the other side of the barrier, even though it 0:14:08.920 --> 0:14:13.280 did not physically pass through the barrier. It's it's part 0:14:13.280 --> 0:14:18.920 of the weird nature of quantum mechanics and probabilistic distribution. Again, 0:14:18.960 --> 0:14:23.000 it's not a certainty, it's a probability. Another concept of 0:14:23.080 --> 0:14:26.080 quantum theory that ends up being very important with quantum 0:14:26.120 --> 0:14:31.400 computers is that of superposition. This is a pretty tricky concept, 0:14:31.440 --> 0:14:35.880 as it is so counterintuitive that it prompted Schrodinger to 0:14:35.880 --> 0:14:39.560 create what he thought was an absolutely bonkers example so 0:14:39.600 --> 0:14:42.120 that he could illustrate how whacka doodle this idea was 0:14:42.240 --> 0:14:45.720 on the macro scale. But today that example is widely known, 0:14:46.120 --> 0:14:48.360 or at least it's known by name. That would be 0:14:48.400 --> 0:14:52.520 Schrodinger's cat. So what is superposition and what the heck 0:14:52.600 --> 0:14:58.000 was that famous thought experiment. Well, superposition refers to quantum 0:14:58.000 --> 0:15:04.000 particles as inhabiting all sable states simultaneously. So a state 0:15:04.080 --> 0:15:08.240 is really just a feature, something that the quantum particle possesses. 0:15:08.840 --> 0:15:12.400 So let's take electron spin as an example. All right, 0:15:12.480 --> 0:15:15.720 So electrons can spin in different directions, and for this 0:15:15.760 --> 0:15:19.320 particular example, let's just talk about spinning up or spinning down. 0:15:19.680 --> 0:15:22.120 So electron can spin up or it can spin down. 0:15:22.160 --> 0:15:25.760 According to some versions of quantum theory and its quantum state, 0:15:26.240 --> 0:15:29.000 that electron can be said to be both spinning up 0:15:29.040 --> 0:15:33.120 and down simultaneously. It's both states at the same time. 0:15:33.360 --> 0:15:36.960 It inhabits them while it's in this quantum state. But 0:15:37.600 --> 0:15:41.200 when you measure the electrons spin, when you observe it, 0:15:41.600 --> 0:15:45.880 the quantum state collapses down into one of the two 0:15:45.920 --> 0:15:49.360 possible states. So you're never going to observe an electron 0:15:49.520 --> 0:15:53.680 spinning up and down simultaneously because the act of observing 0:15:54.040 --> 0:15:58.040 changes that which is observed at the quantum level. This 0:15:58.120 --> 0:16:01.520 is the argument some people make that you know, measuring 0:16:01.560 --> 0:16:04.680 doesn't matter because if you measure, you have changed the 0:16:04.720 --> 0:16:06.840 thing that you were measuring. Now, that is true on 0:16:06.880 --> 0:16:09.200 the quantum scale, but as you move up to the 0:16:09.200 --> 0:16:13.000 classical scale, it's not really something you need to concern 0:16:13.040 --> 0:16:18.440 yourself with. So, uh, you can't confuse quantum mechanics with 0:16:18.520 --> 0:16:24.920 classical mechanics. It they are rules that define two different universes, 0:16:25.000 --> 0:16:28.880 really the quantum level and then the classical level. So 0:16:29.800 --> 0:16:32.000 it's not like classical physics need to be thrown out 0:16:32.040 --> 0:16:34.920 the door. They still apply just two things that are 0:16:34.960 --> 0:16:37.600 on the classical scale. When you get to the quantum scale, 0:16:37.640 --> 0:16:39.400 that's when you have to look at quantum mechanics, and 0:16:39.400 --> 0:16:44.120 that's when you start seeing these seemingly weird and counterintuitive rules. 0:16:44.880 --> 0:16:47.840 And I say seemingly because the only reason they seem 0:16:47.880 --> 0:16:50.560 weird to us is because we cannot observe them directly. 0:16:51.120 --> 0:16:54.240 We don't exist on the quantum level um and in 0:16:54.600 --> 0:16:56.760 the way that we can perceive it. We can just 0:16:57.040 --> 0:16:58.880 work out the math and figure it out, and then 0:16:58.880 --> 0:17:02.400 we can design experiments, and through those experiments we can 0:17:03.600 --> 0:17:07.160 we can actually look for evidence that supports these theories. 0:17:07.200 --> 0:17:10.080 And in fact, that has happened over time. People have 0:17:10.720 --> 0:17:14.280 designed experiments to test these ideas and found through the 0:17:14.320 --> 0:17:18.199 results of the experiments that those ideas seemed worthy, they 0:17:18.240 --> 0:17:23.199 seemed valuable, and and real. Now, Schrodinger's cat is a 0:17:23.240 --> 0:17:26.879 way of exaggerating this superposition effect, kind of in an 0:17:26.920 --> 0:17:29.399 effort to show how crazy it sounds. So here's the 0:17:29.400 --> 0:17:32.919 thought experiment. Let's say you've got a cat, and you 0:17:32.960 --> 0:17:35.919 put the cat in a metal case. Inside that case 0:17:36.000 --> 0:17:39.680 with the cat is a device that contains a radioactive particle. Now, 0:17:39.680 --> 0:17:46.040 that radioactive particle could undergo radioactive decay within the next hour, 0:17:46.960 --> 0:17:51.320 or equally, it could not decay within an hour. So 0:17:51.359 --> 0:17:54.240 there's an equal chance that it could decay or that 0:17:54.320 --> 0:17:58.640 it could remain whole within the span of an hour. 0:18:00.000 --> 0:18:03.360 If the particle does decay, the energy it gives off 0:18:03.440 --> 0:18:07.240 will cause a glass vial containing a poison to break, 0:18:07.600 --> 0:18:09.879 and that will release the poison in the cage and 0:18:10.040 --> 0:18:13.400 kill the poor kitty cat. The whole experiment is completely 0:18:13.440 --> 0:18:16.719 sealed away. The cat is unable to interfere with the device, 0:18:16.800 --> 0:18:20.080 because if you interfere with a quantum state and then 0:18:20.200 --> 0:18:23.480 it decoheres, the whole experiment falls apart. So you have 0:18:23.560 --> 0:18:26.240 to have this is a thought experiment anyway, but you 0:18:26.280 --> 0:18:27.760 have to have it set up in a way so 0:18:27.800 --> 0:18:30.600 that the cat's not going to interfere with the quantum state. 0:18:30.760 --> 0:18:33.480 So an hour goes by with the cat inside this 0:18:33.520 --> 0:18:37.199 cage and the radioactive element in there as well. And 0:18:37.240 --> 0:18:39.760 the question you have to ask yourself before you open 0:18:39.960 --> 0:18:43.199 up the cage is is the cat dead or is 0:18:43.240 --> 0:18:47.960 it alive? Now? According to the super position theory and 0:18:48.000 --> 0:18:51.200 Schroedinger's interpretation of that theory, you would have to say 0:18:51.240 --> 0:18:54.240 that the cat is both alive and dead at the 0:18:54.320 --> 0:18:57.439 same time. That exists in this quantum state where it 0:18:57.520 --> 0:19:00.439 is alive and dead. It is only when you open 0:19:00.480 --> 0:19:03.880 the cage and you look in and you are essentially 0:19:03.920 --> 0:19:07.160 measuring the system this way, because you're making an observation 0:19:07.760 --> 0:19:10.479 that the entire system will collapse into one of the 0:19:10.520 --> 0:19:14.400 two possible outcomes, And at that point the cat makes 0:19:14.440 --> 0:19:18.040 the transition into either being perfectly fine or very much 0:19:18.080 --> 0:19:22.560 an ex kitty cat joining the choir invisible, running up 0:19:22.560 --> 0:19:25.840 the curtain, kicking the bucket, shuffling off the mortal coil. 0:19:25.880 --> 0:19:28.239 You get the idea. This is where you get all 0:19:28.240 --> 0:19:31.560 those jokes about the cat being half dead. But here's 0:19:31.560 --> 0:19:36.080 the crazy thing. While Schroedinger's thought experiment did make superposition 0:19:36.160 --> 0:19:41.320 sound really bonkers, experiments supported the notion of superposition. Now Granted, 0:19:41.640 --> 0:19:44.920 we're talking about effect on the quantum level, not something 0:19:44.960 --> 0:19:48.880 that's observable in our macro world. Schrodinger would argue that 0:19:48.960 --> 0:19:53.560 because the the whole premise of the experiment relied upon 0:19:53.560 --> 0:19:57.040 a quantum particle, whether it decayed or not, it doesn't 0:19:57.119 --> 0:20:01.920 violate this. The consequences of the at quantum event would 0:20:01.960 --> 0:20:05.280 be on the macro level, but that the actual event 0:20:05.359 --> 0:20:08.800 itself would still be in the quantum level. Uh. There's 0:20:08.800 --> 0:20:11.280 some people who dispute that, so it kind of becomes 0:20:11.280 --> 0:20:14.560 a philosophical argument. But the point is that the experiment 0:20:14.640 --> 0:20:18.520 started to support this idea of superposition, and it's one 0:20:18.560 --> 0:20:20.720 of the few, one of a couple of principles of 0:20:20.760 --> 0:20:24.080 quantum mechanics that makes quantum computing such a potentially powerful 0:20:24.119 --> 0:20:27.879 tool and a possible revolution in computing in general. The 0:20:27.960 --> 0:20:31.159 other big concept in quantum theory that is of particular 0:20:31.200 --> 0:20:35.480 importance with quantum computers is called entanglement. Now, this is 0:20:35.520 --> 0:20:40.400 the strong correlation between two quantum particles that link those 0:20:40.440 --> 0:20:43.600 two particles together, no matter how much physical distance might 0:20:43.680 --> 0:20:48.760 separate the particles. So you could take two entangled particles, 0:20:48.920 --> 0:20:50.440 and if you could do it in a way where 0:20:50.440 --> 0:20:53.640 you're not disturbing the entanglement. You could move one particle 0:20:53.720 --> 0:20:56.000 to the other side of the universe from the first 0:20:56.000 --> 0:20:59.840 particle and they would still remain entangled. Einstein would call 0:21:00.040 --> 0:21:04.240 this spooky action at a distance, and entangling particles means 0:21:04.280 --> 0:21:07.359 that these two particles are always going to complement one 0:21:07.400 --> 0:21:11.600 another in some way. So let's take electrons again. Let's 0:21:11.600 --> 0:21:15.160 say you entangle to electrons so that their spin is correlated, 0:21:15.640 --> 0:21:19.240 and if one electron is spinning up, the entangled partner 0:21:19.320 --> 0:21:21.919 is always spinning down. This is just one example of 0:21:21.920 --> 0:21:25.160 a way you could entangle particles so that means no 0:21:25.200 --> 0:21:29.399 matter how much distance separates these electrons, if electron A 0:21:29.520 --> 0:21:31.800 is spinning up, then electron B is spinning down. If 0:21:31.840 --> 0:21:34.680 electron A starts to spin down, then electron B will 0:21:34.680 --> 0:21:37.760 start to spin up, and he'll do it exactly at 0:21:37.800 --> 0:21:41.800 the same time. There's like no delay, and this will 0:21:41.840 --> 0:21:44.720 happen no matter how far apart those electrons are. It 0:21:44.840 --> 0:21:48.160 seems impossible, and yet that is in fact what seems 0:21:48.200 --> 0:21:52.400 to be happening with entanglement. However, once you observe one 0:21:52.440 --> 0:21:55.399 of those two electrons, then the entanglement is broken and 0:21:55.480 --> 0:21:58.919 you will know at the moment of observation, the moment 0:21:59.000 --> 0:22:02.280 of measurement, what that other electron was doing, But you 0:22:02.320 --> 0:22:05.720 don't know what it's doing anytime after the moment of observation. 0:22:05.840 --> 0:22:10.480 You can only say, at this precise moment, the other electron, 0:22:10.520 --> 0:22:15.360 wherever it may be, was doing this particular activity. At 0:22:15.400 --> 0:22:19.320 that point, the system decoheres, and so it gives you 0:22:19.359 --> 0:22:23.720 information but nothing. Some people have argued that this is 0:22:23.720 --> 0:22:26.960 a way that you could potentially have faster than like communication. 0:22:27.000 --> 0:22:29.919 Others argue no, because all it does is tell you 0:22:30.000 --> 0:22:35.480 information that previously existed. The information didn't travel, just your 0:22:35.760 --> 0:22:39.600 realization of what that information was occurs to you. It's 0:22:39.880 --> 0:22:43.359 another fine distinction that gets into philosophical arguments, and its 0:22:43.400 --> 0:22:46.199 outside the scope of this particular podcast, but it is 0:22:46.240 --> 0:22:50.639 a fascinating discussion. So together, super position and entanglement are 0:22:50.720 --> 0:22:53.359 two of the factors that really make quantum computers so 0:22:53.440 --> 0:22:57.240 potentially revolutionary. And it's weird to say potentially, because today 0:22:57.240 --> 0:23:00.840 they are actual working Quantum computers just have a somewhat 0:23:00.880 --> 0:23:03.760 limited scope right now, but they're getting better all the time, 0:23:03.800 --> 0:23:07.240 and in fact, some of the prototypes are really impressive 0:23:07.320 --> 0:23:11.639 already before we get to actual quantum computers. There's a 0:23:11.760 --> 0:23:15.320 little more history I need to cover. In nineteen seventy three, 0:23:15.640 --> 0:23:19.920 Alexander Hollevo argued that for any given number of cubits, 0:23:19.960 --> 0:23:23.560 which are quantum bits, you could not possibly carry more 0:23:23.640 --> 0:23:28.080 information than that same number of classical bits. So, in 0:23:28.119 --> 0:23:31.840 other words, if you have eight quantum bits, those eight 0:23:31.920 --> 0:23:35.000 quantum bits could carry only as much information as a 0:23:35.040 --> 0:23:38.439 classical bite, bite being eight bits, and of course a 0:23:38.480 --> 0:23:40.960 bit being a basic unit of information, either a zero 0:23:41.080 --> 0:23:46.119 or a one. However, the eight cubits through superposition could 0:23:46.160 --> 0:23:51.199 represent all possible states of that bite. So it's not 0:23:51.280 --> 0:23:56.159 carrying more information, it's just carrying Uh. It's hard to 0:23:56.320 --> 0:23:58.320 hard to put this in a way that makes sense. 0:23:58.640 --> 0:24:00.639 It's not carrying more information than a bite, it's just 0:24:00.680 --> 0:24:05.000 carrying every single variation of information that bite could represent. Again, 0:24:05.040 --> 0:24:08.359 anotherir fine distinction. This gets really fuzzy and wibbly wobbly 0:24:08.400 --> 0:24:11.119 timey y me to me. In the early eighties, people 0:24:11.160 --> 0:24:14.920 begin to theorize about the possibility of quantum computing and 0:24:15.480 --> 0:24:19.080 talking about how you might use quantum particles to represent bits. 0:24:19.160 --> 0:24:21.640 So again, like electrons, you could use electrons in their 0:24:21.680 --> 0:24:25.600 spin And this is a quantum quality that electrons have, 0:24:26.200 --> 0:24:28.240 and if you were able to put those into a 0:24:28.280 --> 0:24:31.200 quantum state, you could use the electron spin to represent 0:24:31.520 --> 0:24:34.720 what would normally be a bit in a classical computer. 0:24:35.280 --> 0:24:38.480 That's just one possible example, mind you, because you could 0:24:38.640 --> 0:24:41.440 use all sorts of different stuff to represent these bits. 0:24:41.520 --> 0:24:45.520 You could use photons and their polarization if you wanted to, 0:24:46.160 --> 0:24:51.400 or other quantum particles and other qualities. In Richard Fineman 0:24:51.480 --> 0:24:54.320 presented a talk in which he lamented the fact that 0:24:54.400 --> 0:24:59.520 classical computer systems would be incapable of simulating the evolution 0:24:59.520 --> 0:25:02.159 of a quant um system, because quantum systems would just 0:25:02.160 --> 0:25:05.879