Valley splitting and the hidden clue

3:10:37>> And >> that's kind of like Lincoln in in in Lincoln movie. He was like um to my knowledge there's no Confederate negotiators in Washington DC. Right. And then the the the the Confederate sympathizer in Congress was like that doesn't mean anything. >> Yeah. [laughter] That's a lawyer's dodge. It's kind of what this feels like. >> Okay. >> Doesn't doesn't really mean anything, >> right? Right. >> Here's to here's to underscore that point about about how they're trying to dodge this. >> You know, as you can see, I'm no longer employed at HRL. So, >> this is just stuff that is public, right? I just read off stuff that's in the paper. >> It's in the paper. >> It's in the paper. That's all I just I just read it off. In 2021,

3:11:18they showed valley splitting splitting results. Um, in this paper on the left hand side, um, on the red, the red shows a distribution of valley splitting energies that go anywhere from 300 microeleron volts all the way down to like 10 to 30. >> Mhm. >> Okay. Now, crucially, valley splitting is a difference between energies. So, it's always going to be positive. What this should remind you of is a gausian that's centered at zero. >> Mhm. >> Okay. that they've just like made positive, right? So what this is saying is sometimes we get really good energy splitting where it's really high and so my electrons can be localized in one state and sometimes it's really bad sometimes maybe good sometimes maybe you know

3:11:58>> Jaro Gatuso was I think the gaffer at Latio now where uh the transfer when this is funny Mussolini's greatgrandson now plays for Latio which is the same club that >> Gatuso is the the coach at. I love that video. Like that's [laughter] such a good video. It's so applicable in so many life situations. And this is one of them, right? The valley splitting traditionally it's kind of a crapshoot. >> Okay. >> Um in this paper, the one that's in Nature in the supplement, they have like a 70page supplement that they've uploaded. Um cuz there was a lot of work that was done. Um >> let's look at this latest result. It shows a value splitting of 1.8 mill electron volts. The other one was 300.

3:12:40So that would be.3. Yeah, >> we're going from.3 which was the best that they had to now 1.8 and one. >> These are they're saying typical values of the valley splitting. >> Crucially, they don't show a distribution. >> Yep. >> Right. What they say is that given our error rate is so low, you can tell that it's mostly >> going to be around these values. >> Okay. Okay. >> Okay. >> It is no longer a problem. >> And this is highlighted by the reviewers. You can again this is a nature paper so you can read the reviewer report >> and the reviewer says that the author state um in a certain line that the conventional concerns such as valley splitting are no longer limiting attributing this to quantum well which

3:13:21is engineered to increase valley splitting. >> Mhm. >> Okay. And then he says if confirmed this would represent a significant advance for electron spin cubits. Okay. If this is true this is a big deal. Why is it shoved in the supplement is [laughter] kind of what he's saying right? And then he says the current evidence he says the current evidence is not enough and um you need to show like you know I would expect for example a statistical analysis of valley splitting across devices. So it's like maybe give me a distribution >> right >> you know he's basically saying like how you do that >> right and part of the argument might be well now that we're going private it's partly proprietary >> and that's exactly the response the response from I'm not [laughter] telling

3:14:03you >> that cuz that's kind of the juice. Yeah. >> I mean that is the juice. >> Yeah. Yeah. Um it certainly shows that it's possible which is great for the spin community in general, right? Because it's not an insurmountable like you know 2 plus 2= 5 problem. It is certainly possible and um the response there to the reviewers is we have instead substantiated our claim that value splitting is not an impediment um with circumstantial evidence like the lack of multiple frequencies in your exchange oscillations. Basically, all of these other little things are saying that if valley splitting was still a problem, I would notice it in all of these other plots. >> There's derivative judgments you can make that would that identify it whether it's there or not.

3:14:43>> Yeah. And it's clearly not there. And unfortunately, the proprietary um nature of that information prevents a complete discussion >> of those aspects. >> We got them. >> Yeah. So, >> we got them. >> It It's kind It's kind of interesting, right? It's like another aspect like it sometimes goes under the radar. um just putting it in the supplement, but the reviewer noticed and he brought it up and that's like the that's like a a real I mean based on the history we've talked about, right? That's been the historical reason why the neutral people or the whoever the trapped ions people have been like this is not going to happen because you have to tell me how

3:15:23when we have uh na silicon naturally occurring silicon between isotope 28 and 29 and they have these six valleys >> uh which means that you are going to have this like exponentially exploding calculation you have to do because you can't control the entanglement the thingy is the the way you wanted to. Uh that's like you can't you have to solve that problem before I'm going to pay attention. Yeah. >> And they just kind of Yeah, we solved it, but that's in the >> it's in the supplement. >> It's in the supplement. Right. And it's funny because like the the isotopic enrichment part, that's an open secret. That's how you do it, right? It's just like >> yeah, you just that's a fundamental physics argument. You remove a bunch of

3:16:04magnetic spins from your substrate and then you're no longer going to have the valley splitting part. But that's that's a different, >> right? Yeah, >> it's a little different. That's >> it's a little different. >> Uh but that's proprietary >> proprietary, >> right? But it certainly means that it's possible. There's a chance. And that I think spells great things for the spin cubits community in general. >> Speaking of proprietary, we can get to our our audit. >> Our audit, which is also >> which is also proprietary from first principles audit. [laughter] So what are the strengths for silicon? Well, silicon is a miracle material, right? I mean, now that you if you isotopically enrich it, um, you don't apparently the valley

3:16:46splitting is no longer a thing. The negatives are no longer a thing. Charge noise is no longer a thing. If you fab it in a really nice way like like HRL has done, it's no longer a thing. Um, so seems to me like cubid quality, it's pretty high. >> Quite nice. >> Quite nice. Quite nice. Um, let's go into control. >> Mhm. You see how I'm just breezing through these like Yeah. Pretty nice. >> Yeah. Yeah. I mean, well, we've already explained. >> Yeah. We I I already explained in in in great three and a half hour long detail. >> Yeah. >> So, it's very well established. >> Yeah. That the cubic quality here is is pretty great. It's quite nice. >> Spin cubits DFS in this case, even with lostenzo where you have the magnetic field and like the like a single

3:17:27microwave thing, still it's just the spins going up and down. You can pack them together. You can use exchange which is DC only to to make them talk. It's great. Right. >> Back to basics. >> Now for control >> the gate speeds are really fast. >> Um exchange only gates execute in 1 to 10 nonds. So the same stuff that we liked about superconducting circuits which is [clears throat] the fact that I can run shores pretty quickly in a matter of hours rather than a month or a year. I can still do that here, right? As long as I have enough cubits to to go around. They're actually faster in some cases with superconducting circuits. Um, and they use only bassband.

3:18:07>> The gates are all bassband. It's all DC. >> There's no AC. So, there's no AC leakage everywhere. And I can I can, you know, isolate it from the system. Although, that'll get into scalability part. So, let me not go there. >> Now, what are the negatives with control? >> Mhm.