4,155 words · auto-generated from the episode video
56:43up precision on the other. Yes. And to think about like why would you want to do this? Let's go back to let's go into like a example like LIGO, the gravitational wave observatory, right? Where we want to measure the position of our spin of our mirrors really well, right? So I want to measure um how far apart one leg is another right? I want to do that. Now the way I do that is through interferometry where what I'm really trying to measure is the amplitude of the light that's coming when it goes from on one arm versus the other arm and it comes back it interferes. If both the arms are exactly the same length then the light is going
57:23to cancel and I'm going to get zero brightness. Mhm. >> But if there's a slight offset, then I'm going to get a tiny amount of brightness in my detector because the light is not exactly canceling out. >> The only thing I care about is the amplitude. >> Right. >> Right. >> Yes. Yes. >> And and I I couldn't care about let's say the frequency of the light. >> Mhm. >> Because I know that the laser is my frequency. >> Right. >> Right. Right. >> So this is just like something that I've I'm I'm sort of doing a back of the envelope here. Obviously there's other things, but that's the idea. Yes. >> What if you only care about one thing in LIGO? The only thing I care about is the amplitude of the light. >> Yep. >> Right. Yes. >> Because then I can make this >> this kind of gravitational wave drawing.
58:05>> That makes sense. >> Okay. >> Yes. >> So the challenge is there's incompatibility between different observations. For example, what I was saying with the position and momentum, Heisenberg says you can't measure both at the same time. And the other thing is what if I want to measure at two different spots in space? Okay, that is what so what ends up happening is you've got like two different spots in space. What you can do is instead use entanglement. This is your quantum action at a distance. Spooky action at a distance, right? This won the Nobel Prize a few years back in um in physics. We always use Alice and Bob
58:46for these um experiments. I don't know why there's even a quantum company called Alice and Bob because that is what we use to show entanglement and teach entanglement. You get a pair of particles, you send one particle to Alice, you send the other particle to Bob and then you ask one of them to measure their particle and that's immediately going to affect in some sense the measurement that Alice has. >> Okay? Because these two particles because they're entangled, they're connected to each other across space and time through some weird mechanism that's like kind of faster than speed of light, but like not really, but there's nuances. But what ends up happening is if I measure the spin of here, that's
59:26going to affect the the spin here. At least that's what it looks like. The two are correlated even across these distances. Okay? Mhm. >> And what these guys figured is well actually what we could do is maybe use this >> to then up our game in terms of measuring different things at different locations. >> Mhm. >> Okay. >> Mhm. >> They use something. You see what I'm saying? >> Yeah. >> Like >> we'll get into it. The first Bose Einstein condensate, that's what they used. The first Bose Einstein condensate was in the late 1990s in Boulder. They made it. This is kind of sometimes colloquially called the fifth state of matter. What you end up doing is cooling
1:00:06atoms down to just above absolute zero such that all of these individual atoms behave like a single entity. They behave like a single quantum wave packet. >> Yes. >> Okay. They're just riding on top of each other. What these guys did, Lee and others in 2026 in this particular paper is they created a Bose Einstein condensate and then they spatially split that macroscopic entangled state and made a bunch of different atomic sensors that were entangled with each other. Made an array and then they could per could estimate whatever thing they were trying to estimate across these different
1:00:47things while still maintaining entanglement. You guys, you guys, this is I I just I cannot get over how creative >> Yeah. >> some people are in at the edges of our understanding >> and being so clever because I can already I can already see where this is going. But let me let's continue because I'm curious about a couple of details but I think you're going to get to them around around how because ultimately what we're trying to be able to do is not only before we talked about increasing precision in one dimension >> we because of the Heisenberg uncertainty
1:01:27principle we can't know two observable states with high precision and this is sort of been the boogeyman that everyone's been trying to work around >> and this is see appears to be a very clever way to hijack >> yes >> the limitations using quantum. >> Yes. And that multiple parameter is what's interesting, right? Because what you could do is say, "Hey, what if I just measure the position over here with the momentum over here?" >> Yeah. Exactly. >> Cuz those two I you never said >> you didn't you know what I mean? >> That's what's happening. >> Yes. That Okay. Got it. Okay. >> So So how did they do it? They they've got this thing called the atomic chip. It's microfabricated gold wires that create this these very steep magnetic
1:02:09field gradients. Okay. And with those very steep magnetic field gradients, you can trap rubidium 87 atoms and you can use those rubidium atoms as a two-state cubid system because the the outer at the outer electron of that rubidium atom, the spin of that could be either with the nucleus or opposite the nucleus. The same way we talk about the hydrogen hypersplitting, this is the rubidium hyperfine ground state. >> And that's a two-level system. You can tightly confine that thing and you can have the atom transfer between you know either the electron spinning this way or spinning this way by sending in a radio frequency pulse. >> This is our zero or one.
1:02:49>> So you've got you've got a kind of cubit here, right? And you can tightly confine this this cloud of atoms near that chip surface. And when you tightly confine it at really low temperatures, you get a Bzon stone condensate. >> Okay, great. That's no longer that cutting edge anymore, which is kind of crazy to think about, right? That in like 20 years it's like, oh yeah, okay, fine. You made a beat Bose Einstein kind of say, great. >> Yeah, cool. Good for you. >> Yeah. Next, what you do is you split them apart. Okay. So now using your radio frequency, >> what you can do is toggle that atom and very slowly turn this single potential well, which is where the atoms are
1:03:30sitting. You can start making a little hill in the middle >> and the atoms are going to split into two two wells. >> Okay, you got to do this very very slowly. >> Okay, you got to do this extremely slowly. Adiabatically is what we call it. And when we get there, we're going to create these radio frequency dressed potentials where you have multiple little wave packets of atoms. So a single atom is now being split up into multiple different clouds that are still entangled because we did it slowly enough that the entanglement of that original Bose Einstein condensate is splitting. And just as a quick note just for my recollection about Bose Einstein
1:04:12condensates, the idea there was, you know, when what you were able to do is you create one sort of macro object >> that maintains all the parameters as one sort of holistic thing as opposed to like indiv. >> It's one wave function. Yeah. >> Which has its own inherent value. Yeah. >> Uh in and of itself. Yes. And so now we're building on top of that concept to take that like macro like this one wave function across multiple >> component parts and we're now splitting it where they are maintaining entanglement. >> Yeah. >> Um which is then going to be our next but I just want like I'm correctly understanding the idea behind the Bose
1:04:53Einstein condensate. >> Exactly. Yeah. It's one wave function that we're now splitting into I guess two wave functions but the two- wave functions because they were derived from the first one and we're doing it slowly enough the entanglement is still very strong >> okay right and now what we can do >> with those multiple clouds of atoms >> is we can measure one quantity here >> we can measure another quantity here another quantity here so on and so forth but because they are entangled these are not independent dependent variables and so the noise is not independent. This is what's crucial. Okay, if they were independent, what would happen if they were independent? Let's say I've got um
1:05:34atoms atom cloud A and atom cloud B. Okay, I measure some parameter on atom cloud A. That's going to be let's say you know A plus or minus some number because that plus or minus number is an error. >> Yes, >> with B I'm going to measure plus or minus some number, right? If I wanted to calculate let's say a difference between what is A and what is B and things like that those errors would be independent and when I calculated that sum or that difference the error would only go down by one over the roo<unk>2. >> Okay. >> Okay. Because they're independent. >> Yes. >> Now when I measure a plus or minus something and b plus or minus something that plus or minus is not independent. They're related. Mhm.
1:06:14>> So what I could do is measure something like a + b and a minus b. Or if I have three things, I can measure a plus b plus c, a minus b plus c, a minus b minus c. I could measure all of these different combinations. And the noise in that total measurement is going to be smaller than if I would have measured the two independently. That is the key. >> Oh my. Does that make sense? >> Yes. Yes. We're doing like >> number magic here. >> Yeah. Yeah. >> We're like measuring combinations of states rather than individual states. And whereby we do that because the noise is correlated because the stuff is entangled. >> Yes. >> The total noise is smaller
1:06:55>> is smaller on on the aggregate comput on the aggregate measurement as opposed to the individual measurement. >> Fascinating. which goes back to now now I'm thinking about that original chart we looked at with the circle and the oval >> and the implications on the level of precision because the noise is now >> smaller because we're make we have this aggregate measurement that >> allows us to decrease noise >> this >> does that kind of make sense >> it it does and this feels very cool because in theory >> let me pause let me let you continue >> yeah so let's see let's see how they actually did it right so they as I said they've got um they've got a single wave function >> with the boss and condensate. Now let's
1:07:37see what they do with just two clouds. So when they do two clouds, they've got this local microwave that you know splits it into two clouds. There you can actually see the sort of two clouds right next to each other about like a few um tens of microns to hundreds of microns apart. Yes. >> Right. And what we're going to do is measure some parameter which effectively means we're measuring like a phase of the wave function. It's like an angle difference between the two things. like we're measuring an angle at all times, >> okay? >> Um on something called a block sphere, but we don't have to get into that. We're measuring some parameter. Okay, the two parameters are correlated. And that's why when you look at, you know, if we were to measure phase 2 versus phase 1, the the clouds are not
1:08:18completely circles. They're spin squeezed. They're these ellipses, right? >> One direction is the sum >> theta um like phase one plus phase 2. The other direction is the difference phase 1 minus phase 2. What you can measure is let's say on one end we measure the sum which is the axis perpendicular to the ellipse. So that's the squeezed axis the part that's like shorter on that ellipse. We measure that >> and then what I can do is rotate the second one. >> Mhm. >> So that now I'm >> the the squeezed axis is on the difference part >> and now I measure the difference. >> Okay. That's another key thing. They
1:08:58they could rotate and manipulate these things such that whatever axis they wanted to do, that's the one that would be squeezed. Okay? So, you've got this ellipse and you're like, I want to measure here now. Let's rotate now. I want to measure here. So, they're able to do both. It's not at the same time. So, you're still not cheating. Yes. Right. Heisenberg is still happy. >> Yes. >> But at different times, you're getting these measurements. >> You've measured the sum in one. You've measured the difference in the other. So, now with the sum, I can find the average value of this parameter. >> Yep. with the difference I can find the gradient I can find what is the difference between here and here right and I'm still keeping Heisenberg happy >> but because of this entanglement and all of the fancy tricks that I've done >> yes >> each measurement now of the sum and the
1:09:38difference >> I've beaten the standard quantum limit >> right >> right because I'm not measuring independent >> I'm not measuring phase one and phase two and then I'm taking the the difference I'm actually just measuring the difference >> yes right through through through this mechanism of the atomic sensors in the Bose Einstein condensate which gives you >> a level which gives you >> uh this mechanism by which to be able to measure where now the uh aggregate measurement has less noise than the independent measurements. >> And because you can now also rotate in the way that you described it, we can get a level of precision across multiple
1:10:20observable states >> instead of having to choose one or the other. So in the LIGO example you talked about earlier examples we just care about one >> you know thing which is the the mirrors with this conceptually you can now expand that to say we care about two things and we can now get a level of precision above the SQL >> closer to the Heisenberg limit which is theoretically the actual limit of observational precision >> yeah we can't get better than that but we'd like to get as close to that as possible and here what we're doing is we're measuring the actual equal let's say difference, right? We're measuring 4 - 3 equals 1. Before we were measuring four, three, and then we'd have to do
1:11:00the math to be like, okay, 4 - 3 is 1. Here we're just measuring one. >> Mhm. >> And the plus or minus on that one is much smaller than we would have done otherwise >> because the four and the three would have had their own individual error. And so the noise at the when you get to the the >> conclusion is much higher. We're actually observing the conclusion with Okay. Very very very fascinating. And now with three we can do all three combinations, right? With three I can do the plus+ plus - plus plus - so on and so forth. And the >> diagonals that you see is what they're actually doing, right? Like what what are you actually measuring? This needs to be a proof of concept, right? It's not like they're measuring some magnetic field that's changing because if you
1:11:40were to do that as a first experiment, >> you'd be like, well, how do you know you even measured it correctly? >> Correct. Yeah. Yeah, that makes sense. >> So what you do? What do you do? You actually encode the parameter. you engineer in and you encode the parameter and then you say can I measure >> what I encoded >> so you ultimately know what the result is prior to measurement such that it's controlled >> yeah because this is a controlled experiment this is a proof of concept right you need to show that it works on stuff that you already know the ground truth for and that's what shows in the in the diagonal it's like they're trying to for the off diagonal stuff it's like you you encode something but you're trying to measure in some other state like you encoded plus+ minus but then you try to measure plus+ you're not able to do that because that wasn't the point but That's and that's kind of the point of that diagonal. Along the diagonal,
1:12:22you get this um boost in sensitivity. Okay, that's the negative decb. The negative dB is how much more boost do you have over the quantum limit? You're getting like five dB, which is like a 3x improvement >> improvement. Right. >> Right. And that makes sense. The point is, you know, the you in order to be able to con sufficiently prove and convince that this is true. You need to be a be able to show that it measures something we have a discrete value for. >> Yeah. Yeah. Yeah. It's like something you've engineered that you know the ground truth for and then you're like, "Okay, I was able to do this. Now I can go and use this to measure other stuff." >> Yeah. Right. Yeah. That makes sense. >> And the applications for this are very cool. Okay. So, for one, you can measure
1:13:02magnetic fields really, really precisely. Mhm. >> You can create kind of like a vector camera that images the full magnetic vector field. So you have the X component, the Y component, and the Z component >> of some material, let's say. >> You can create this sensor now >> and measure inside that material the magnetic fields >> in each direction. You can do this like trick where it's like, okay, now I care about X. Let's measure X. Now I care about Y. Let's measure Y. I mean again you're not going to do it simultaneously but if you do it a thousand times and you have reasonable assumptions about how constant the magnetic field is you can get to pretty nice precision right you can just repeat the experiment over and over again um internal you can have
1:13:44a quantum internet of clocks >> okay so you know with by entangling atoms at different sites in a kind of lattice what you can do is have a distributed clock network >> where there's a clock here there's a clock here extremely precise based on this two levels splitting and and then you can measure gravitational red shifts >> at the millimeter scale. Meaning I have my Bose Einstein condensate here. >> I raise it by 1 millm. If I raise it by 1 millimeter, it's going to feel the Earth a little bit less. >> Mhm. >> By a millimeter. >> Yeah. >> If it feels the Earth a little bit less, time is going to be sped up a little bit
1:14:25more. And you can actually measure that by having the clock decide where it is on a millimeter scale. Right? And finally, if you're like interested in dark matter, there's this one um you know theory of dark matter and of like if you want to measure gravitational waves, when a gravitational wave comes through, the each different part of the sensor is going to feel the gravitational wave at different time points. So you can measure it that way. If you've got a dark matter particle or a dark matter quantum wave that goes through, you're going to get a jitter. And so the the more sensitive we can get, the better we can measure these really really tiny things. >> Because the point is at each points of the measurement apparatus, you're going
1:15:06to have up to a 3x uh increase in level of precision, which when we're talking about gravitational wave detection is extremely valuable. >> Yes, it's extremely valuable. And I mean for their proof of concept, you know, when they when they went from two at the level of two, I think they got about a 3x precision. When they got to three, they didn't have a 3x. It was only like maybe, you know, 50 10% or something like that, which is fair, right? Which is fair. Um, >> but it's a proof of concept, right? The we need a large number of atoms. Right now, they've only got about 5,000 atoms in this Bose Einstein condensate. If you had something like, you know, 10 to the 6, a million atoms, then you could start competing with classical sensors, right?
1:15:48And then if you have even more, now you're really going gang buster. >> Yes. Yes. >> With your with your improvement. You're really hitting that Heisenberg uncertainty limit, right? >> This is quite this is quite quite nice. >> So it's it's a it's a proof of concept. We're we're transitioning to this multiparameter quantum metrology, >> right? >> Mhm. >> And it's going from theory to experimental reality. And I was reading about it. It's like even the theory of this was not really well founded, >> but they're running with it and they're showing that the experiment kind of works. It's very very cool. >> This again is out of the physics department at the University of Basil >> as well as the laboratory Castell Brussel at the University of Sorbon in France. The Europeans
1:16:30doing well. A quantum >> the French doing well. >> The French doing well this we have had a lot of French >> uh French stories in the last couple of episodes. Um, very fascinating. Um, especially because like we talk about all the time, the Heisenberg uncertainty of principles is one of those things to me that's still so weird. >> Um, the analogy I always kind of bring up when we talk about it is like, and this is probably the common analogy in video games, uh, you reach the edge of the level, the map, the edge of where the developers built the map, >> and you can't >> can't go beyond the edge. >> Like that's the limit. >> Yeah. >> And it's just the limit. Yeah. >> And that's it. >> And that's it. >> And you can never know what's outside the limit or and it's a crude analogy,
1:17:12but um >> it's very weird. >> It's it's just very weird. >> It's it's it's a central tenant of of quantum mechanics. It's what makes it so different from classical mechanics. >> Right. Right. >> Right. Uh beautiful. We always love a good solid physics story. We are going to end with our final story of the day which is uh about Alpha K. >> Yeah. uh which is this local adaptive mapping uh that's specific for cancer research. This was in nature communications from the H. Lee Moffett Cancer Center and Research Institute integrated mathematical oncology. Uh this one there's a lot of concepts we've
1:17:54talked about that have helped me kind of gro this concept uh I think a little bit better because you know I didn't understand what gradients and gradient descent was before and things like that and there seems to be conceptually some some overlap here and so now I have a mental model for us to work with but what do we have going on here in this sort of new