Neutral-atom quantum computers

1:50:59that are actually trying to do neutral atoms. Qera, Pascal, Atom Computing, or atomic is a new one um that came out of Caltech actually and it raised like $300 million on low cubit quantum computing. Their idea is that they actually don't need that many cubits. >> Okay. >> Um, their physical to logical cubit ratio is very low. >> Okay. >> Okay. That's the that's the claim they're making. >> Okay. >> Um, but let's let's try to get behind the PR hype here. Okay. So, what is a cubit? >> So, like like trapped ions, the cubit is a real pristine atom, but it's not ionized. U most of the time it's like a rubidium atom or a cesium atom. These

1:51:39are coincidentally the same atoms that are used in atomic clocks >> and for a very good reason because they're highly tunable um highly precise. the transitions are like highly precise and you can manage them very well with like lasers. Um there's no electric charge and because they're neutral we can't confine them using that paw trap trait right with the electrostatic um fields. >> So instead you trap it in midair using optical tweezers. I shouldn't say midair really it's mid vacuum >> right um but you trap it with an optical tweezer. It's a highly focused laser beam where because of the physics of the laser beam being focused, the neutral atom wants to live at the focus of that

1:52:21laser beam. There's like a dipole force that happens that restores like every time the atom moves away, there's a dipole force that restores it back. >> The cubid states are 0 and one. And again, it's the hyperfinine clock states. >> Is it? So, it's just we basically can point at it and be like, "Stay right here." >> Mhm. Yeah. There's like a laser. You concentrate it. You make it stay right there and it's the same super stable spin transitions that are used in atomic clocks. It's like a tractor beam. It is kind of actually a tractor beam is like Yeah. Uh [laughter] that's exactly right. It's a it's a it's a tractor beam. >> Um >> now the problem um actually before we get into the problem, how do we talk to it? Well, we

1:53:03use lasers. Just like trapped ions, we use lasers. Single cubit gates are driven by two photon um ramen laser pulses. We don't have to get into it. Two cubit gates are a bit different. Now instead of using sound waves like we did with trapped ions, >> we are going to use something called a Ryberg state. >> Okay? >> And the Ryberg blockade. Here's the idea. >> You pump a laser into it >> so that the electron that's on the outside gets knocked to a really high energy level. >> Okay? [clears throat] >> Okay. Like imagine you're taking um an electron that's in the orbit of like Earth near the nucleus and you're knocking it all the way out to Pluto. >> Oh, yes. That's quite quite some distance.

1:53:43>> You've increased the size of the atom by a massive amount like almost by a factor of a million >> because now the orbit of the electron >> is like it's like out where Pluto is >> kind of right now because this atom is now very big and its neighboring atoms are still the same size. Let's say it's going to start having effects on the neighboring atom. The neighboring atom is going to start getting nudged. That physical volume is going to start nudging this atom and that massive shift is going to make the other atom shift its energy levels. >> Yeah. >> Okay. And then whatever laser can no longer excite the other atom.

1:54:26>> This is how you do entangling effectively. You're making them talk based on something called a Vanderwal's force which is like volume like becoming fat and making the volume do the talking. So again so previously we use sound as the basically the vector by which we you know had the communication between the cubits. Now we're seeing this like very like fast almost instantaneous uh massive change in volume has these derivative impacts on the other cubits in the system and like that's what's communicating. Then we're going to make it go from the current size to very very big in a very particular way because we then know how that volume change is

1:55:07going to impact the other cubits and then we re that's the way to communicate >> the zero one the two to communicate in this two cubit >> plus states >> plus states. Yeah. Yeah. It's how how you make the cubits talk to one another is >> blow it up and then because this thing is blowed up the other stuff is going to be like whoa and that's your entangling and that's your two cubit gates. >> Interesting. Interesting. I mean, I wouldn't do it that way, but whatever. >> Look, you know, >> interesting. >> Um, so one of the problems here though is that um so with the with the trapped ions right >> because it was an ion hyperfine frequency and like the difference between the zero and the one is very far

1:55:48away from the infrared stuff that we see at room temperature. Right >> here though, the thing is not ionized. It's just at a really high Pluto orbit. And there was this goes back to the rungs of the ladder. >> Yeah, the rungs of the ladder. Before the rungs of the ladder were very big. So then if infrared came in eh doesn't matter here though because you're now at a at Pluto's orbit. >> Yeah. >> Um Pluto plus one is actually kind of nearby. >> Yeah. >> So the infrared bath that I'm in might actually start knocking you into these other registers >> in a way that entrapped ions it did not. >> It did not. Right. So that's a problem that they need to deal with. Okay. >> Um, oh, let's go into cubic quality now. Let's go into the FFP audit. Um, the strength here,

1:56:30>> you [snorts] can pack thousands of them into a tiny 2D or 3D array. >> Okay. >> Okay. You can have a bunch of these optical tweezers and you can make a grid. Like this is kind of cool. You've got a grid of neutral atoms [clears throat] >> that are all together, >> right? That are like packed in. And each of those is a single atom that you're looking at that's like that's like suspended in a checkerboard pattern >> in a sunbeam. >> It's kind of cool. Um and each of these each of these is spaced just like five or four or five microns apart. >> Okay. So it's quite small. >> So it's quite small, right? Yeah. And the physical [clears throat] density is quite large, right? That that's actually pretty cool architecturally. >> Architecturally, right? And now a lot of these a lot of these groups, they report

1:57:11fidelities that are really high. 99.5% gate fidelity. like the the way that they're moving these things around, it's like very very accurate. But you read the fine print.