Trapped-ion quantum computers

1:27:29>> So, next up, trapped ions. Quantum just had its IPO $15 billion. >> Quant Quantinuum. >> Yeah, Quantinuum. >> I love that. >> Um it debuted on the NASDAQ. IPO. >> Yeah. Um it's another one is ion Q that's based out of Maryland. These two companies do trapped ions. Lots of UCLA physics people actually um are involved with Quantinum. Their chief quantum architect is Anthony Ransford who told me himself that he's a fan of the podcast. >> Uh shout out Anthony. Shout out Bruins. Bruins Nation. >> Yeah. Yeah. But you still got to go through the audit. [laughter] Hopefully hopefully you still you still agree to come on the podcast. >> We shall see. >> So what is the cubit? Okay.

1:28:11>> Now, this is not a man-made circuit. They are using an actual literal atom. >> All right. Um, usually it's something like uturbium or barerium. >> Um, what they do and in this case it's barerium, right? Barryium's got these two ion, two electrons on its outer shell. You remove one of them, then it becomes a positive ion because now there's more protons in the nucleus than there are electrons around it. And now the whole thing has a positive electrical charge. Now, because of that charge, you can now move it around using electromagnetic fields. Um, >> there's a key way to do this, though. You can't use a static electric field. You can't just put a bunch of like electrodes at certain voltages and trap them because the ion's going to figure

1:28:52out a way to to to just like shoot out. So, instead, you have to oscillate the electric fields. Um, you can find in one direction and these two other directions, you like, you know, you go positive, negative, and then you switch from negative positive. And this back and forth is sort of massaging the ions to stay in a certain spot. And that is [clears throat] how you um confine a bunch of ions in a single location. This is called a pole trap. >> And this is basically how we're trying to create the cubit states. >> Yes. Yeah. We're trying Well, first you got to localize it. Right. Right. Right. Right. >> Right. With the transmons, it's like, oh, it's on a circuit like it's like right there. Right. >> Right. But with with atoms now, I got to put them I got to keep them in a spot.

1:29:34And so the way you keep them in a spot is using this oscillating electromagnetic field that like oscillates at a certain frequency. >> It's funny because before we were talking about oscillation from like the microwaves and how it coming back to that same idea. You have to maintain the state via oscillating somehow >> somehow. Yeah. It's there's harmonic oscillators are everywhere >> in in physics to be honest. Um so that that's how you like keep the ion in a certain spot. Okay, the cubid states, the zero and the one. These are two very specific stable energy levels of the atom's outermost electron. Um, we've seen this photo before of the hydrogen hyperfine transition. This was sent on the Pioneer probes and the Voyager

1:30:14probes where the electron on the outside of the hydrogen is either parallel to the spin of the proton or it's antiparallel to the spin of the proton. And the difference between those two is 1420 megahertz. Um, and that's sort of that set the time on the pioneer record that we sent out for the aliens if they wanted to decipher where we're from and how to locate Earth and things like that. This is called a hyperfine transition. It's when the electron is parallel to the nuclear spin versus opposite the nuclear spin. The trapped ion people, at least in quantum, they're using these two as their zero and one. >> Okay. >> Okay. That's their zero and one. And the way you um interact between them is

1:30:56using lasers. >> Laser beam, >> right? And um the energy scale between these guys is about 12 GHz. So it's in the microwave frequencies. >> Um and that temperature is equivalent to about 600 ml. >> Okay. >> Okay. So the the temperature difference or the energy difference between your 0 and one in this case is less than a Kelvin. >> Okay. >> It's it's larger than the superconducting So larger than superc conducting but still less than a kelvin. >> Yeah. My my point is here this stuff still operates at room temperature though. >> Okay. >> The question is why? Um it's because it's you suspend it in a vacuum. >> If you put it in a vacuum then nothing is interacting with it. There's no atoms that are jiggling around that are like

1:31:37poking it hopefully, right? if the vacuum is good enough and all of the electrons I mean sorry all of the photons because remember at any given temperature there's not just degrees of freedom at the with the atoms that are moving around but also there's degrees of freedom with photons and the electromagnetic field and so in this room itself in our for example in our body there are photons that are jiggling around at around infrared because we are at about 300 Kelvin now there's going to be a bunch of photons that are poking this ion thing right at 300 Kelvin. It just so happens though that a lot of those photons are in the infrared. [clears throat] >> And those infrared photons are very different from the energy gap between

1:32:19the zero and the one. So they just sort of >> coast through. >> Coming back to our rungs of the ladder. They're not in the at the range that matters for us in what we're looking at the rungs of the ladder. >> Exactly. Yeah. Uh that was a question that I had when I was researching this. It's like, okay, fine. Like, it's a vacuum, but like you're still you have an ambient heat bath of photons. How come how come that doesn't destroy you? Well, it's because these guys just aren't sensitive to that. The rungs of the ladder are very different from the the poking that's happening, right? >> Mhm. >> Okay. So, um, how do you talk to them? Well, you use lasers. You line up a chain of these glowing ions in a trap so that you've got chains of ions. Um, single cubit gates are done using

1:33:00precisely tuned laser beams on the individual ions. Um, and then two cubit gates are where it gets kind of wild. Okay. >> Okay. So, two cubit gates are done using effectively sound waves in your ion mesh. >> Okay. >> Okay. Um, these things are charged, right? Which means if I move one guy the positive it's positively charged so it's going to repel everything else >> because we've removed the two uh one of the outer shells. >> So it's like just a barryium plus. >> Okay. >> And um and we use the remaining outer shell as the hyperfine right got it. >> Um but if I move one of these barium atoms that's going to cause a coolum repulsion and electrostatic repulsion on the other one because you know like charges um

1:33:43do not attract repel that's the word. Um, and so if I if I move one of these guys, that's going to move one of these guys that's going to move one of these guys, right? And those phonon modes, those sound waves are how you start entangling and doing two cubit gates. It's kind of interesting, right? >> That's interesting. >> That's interesting. >> Yeah. Yeah. I I thought it was pretty cool because now now it's just another means of Is this now I'm trying to think about it. This is how we measure. This is the measure the >> No, this is how this is how we do two cubic gates. So, how we entangle them, how we get them to talk to one another is using sound waves. We read them out and measure them using the lasers.

1:34:23Again, it's it's effectively imaging. It's like you you poke it with and and you try to see is it in a this state or this state. Is it zero or the one? >> That's interesting. But the the the way in which we're having them entangle or interact is via sound waves. >> With sound waves. >> That's interesting. Isn't that cool? Yeah, that's that's quite nice. >> Yeah. It's called the um mulmer sorenson gate. >> Okay. >> Okay. >> Okay. >> Um and and that's it's the jiggling >> of of the sound waves between these ions that's actually doing this. So, okay. How does this hold up with the FFP criteria? And this is a chip that that shows right in the center. You've got this line. >> Yeah. Yeah. Right in the middle. Okay. Okay. Okay. >> Um Okay. So, how does it hold up with the FFP criteria? The strength.

1:35:07This is mother nature's ultimate cubit in some sense because every single cubit is identical. Before with the superconducting thing, you know, you got to manufacture it. Each thing is going to be different kind of by design because you want the resonant frequencies to be different. Here everything is exactly equal and as long as I can point my laser accurately, >> right? >> I can be like, okay, talk to this guy now talk to this guy and so on and so forth, right? So every single cubit is actually the same. There's no like two-level system causing headaches that are in the background. Um the other thing is the coherence time is pretty ridiculous on these guys. >> How long again coherence time being how long it remembers the zero and one so you can then ch manipulate or read.

1:35:49>> Yeah. >> And I ultimately mess with and mess with it. Ultimately we want as long of a coherence time as possible. >> Yeah. This thing can get to 10 hours. >> Okay. That's >> right. I So I I I take an ion. >> Yeah. >> I put it in the zero state. I come back several hours later and it'll still be in the zero state. >> That's that's quite nice. >> That's quite nice. >> That's quite nice. >> Right. >> Okay. [laughter] >> That No, that >> that's that's quite nice. >> That's a big That's a big deal cuz that's that's a totally different category than what we were talking about with superconducting cubits. Yeah. >> In terms of coherence. >> Yeah. Yeah. They're like they were they were happy with a millisecond, >> right? This we're we're just in >> here. We're we're doing hours. >> Okay. >> But >> okay, >> there's a caveat. >> Okay. with the superconducting um a

1:36:31millisecond was great because the gate times were nanconds. Yeah. >> Right. >> Here the gates are really really slow. Okay. >> Because we're using sound. >> Yeah. And sound waves are >> sound waves are kind of slow and there's actually an upper limit to how fast you can do these gates and it has to do with how fast the the p traps are going. like you know the the the the thing I was showing you earlier with the electromagnetic fields like kind of maintaining these ions in a geographic position. >> Those things are are creating like a sort of bowl that is like it's it's really a saddle. You know those saddles it's like creating a saddle that is rotating around. The rotation rate of that saddle is kind of like an upper

1:37:13limit on how fast my gates can be >> because the the the ions are moving around in that saddle. Right? If you try to like it's kind of like imagine if you're like um two people on a swing, >> right? And and you're swinging back and forth. >> That swinging back and forth, let's say, is the electromagnetic saddle that is keeping you there, but you're trying to communicate using the beam that is connecting you. >> Mhm. >> Um in the playground, right? You're trying to communicate with the person next to you based on like how you can vibrate the beam above you that is holding you together. >> Yeah. Yeah. >> There's going to be a limit to how fast you can make it. And and part of the then what this means is because that gate time is now slower.

1:37:53>> Yeah. >> Um you know even though our coherence time is very long, you can just do less. >> Yeah. >> Right. Like the >> Yeah. Yeah. Like the coherence time is way longer but you can do less with the same amount of just physical time in the lab. >> Right. Right. Right. >> Right. Right. And so just because you have you would ideally want a longer coherence time and really short gate time. And so we're like yeah we have long coherence. But we're now having a much longer from as compared to superconducting cubits longer gate time. So you can just basically cycle to do stuff less frequently. Is that >> Yeah. Yeah. Yeah. So it's like it's like the scale of the quantum circuit that you're trying to implement might actually be the same, >> right? Yeah. >> Cuz both of the things have scaled,

1:38:34>> right? Exactly. Exactly. Exactly. Okay. Yeah. Yeah. Yeah. >> So um so that so that's that's one of the caveats, right? Um