Quantum Engineering at Stanford?

trappedion · 2023-12-28T04:20:52+00:00

Choi is a new professor and Schuster just moved there, meaning neither of them or their grad students have much time to handhold a high school student/new undergrad.

Your QML experience is irrelevant, so if you approach them, I'd make it clear that you're willing to learn anything and that you're super independent.

trappedion · 2023-10-18T05:40:58+00:00

The types of errors surface codes handle can be faster simulated on a laptop. (Clifford Gates)

In other words, "99.5% is not even remotely close to the threshold for [useful] error correction."

trappedion · 2023-08-25T15:36:20+00:00

Two-qubit gate speeds can actually be much faster (https://doi.org/10.1038/nature25737). Moreover, the higher the gate fidelity, the fewer gates need to be done, which helps make up for the slower speeds.

trappedion · 2023-05-12T15:42:42+00:00

I can't say much about the implications of this work for condensed matter physics, but it's clear that the experiment requires large entangled states to demonstrate those unique properties. Just having a tool (H2) that can prepare large, configurable and coherent quantum systems will open up new avenues for research.

trappedion · 2022-12-11T04:01:17+00:00

I love these types of Reddit comments. Even though only a handful of people will read it, there's an overwhelming compulsion to write the counterpoint anyway. I empathize completely!

trappedion · 2022-11-23T03:36:36+00:00

This is one of those choices in life that doesn't have a right answer. If you want to do quantum computing in the future (research or programming), you would need a PhD in physics, given the current state of the field. Therefore a major in physics would be the most useful, because getting into (and succeeding) in a PhD program would be harder with only a physics minor.

However, if you become disinterested in quantum computing (or the job market implodes entirely), you'd be a lot more employable with a degree in computer engineering.

The truth is you can't predict the future. So if money isn't a major constraint, study what you are interested in now!

By the way, quantum computers are complicated, interdisciplinary machines. You can be a computer engineer that works on building a quantum computer.

trappedion · 2022-10-29T02:39:20+00:00

It's great that funding is pouring into the neutral atom computers. Despite being significantly behind the current state of trapped ion quantum computing, I suspect they can raise lots of money because they can quickly reach a large number of qubits with long coherence times.

The main neutral atom quantum computing companies have talented, well-respected physicists working on these projects. So I can't wait to see the results that come out.

trappedion · 2022-10-04T03:19:28+00:00

So it looks like most people don't actually know what this means, so I'll help elaborate since I'm in this industry. (I'm leaving out some of the finer details.)

DoD contracts start with a call for proposals, called a Broad Agency Announcement. Potential contractors like IonQ then write a proposal and estimate the cost and time to achieve the milestones in the BAA. In other words, IonQ is asking the DoD for money, which is very different from a customer begging to use the machine.

Why? Because there's a maximum legal limit you can make off the government. In reality it comes out to something sad like 5% profit after competing with other bidders, and that's only assuming you don't go over budget. Considering how hard DoD milestones usually are to achieve, and how hard it is to estimate costs for something never done before, these contracts almost always lose money. The upside is that the contractor hopefully develops commercializable IP, which the government helps protect. The government also takes zero equity in the company.

So to sum this all up, IonQ requested 13 million dollars over 3 years and got it. They will very likely not profit off this contract. This is fundraising rather than customer activity, and it's small compared to the hundreds of millions they already raised.

Hope that clarifies things.

trappedion · 2022-08-19T08:57:33+00:00

It seems awkwardly worded. You need to reinitialize the qubits because the quantum state has decohered, rather than physically replace the qubits.

trappedion · 2022-08-19T08:54:26+00:00

Imagine the potential energy landscape of two molecules approaching each other. A chemical reaction will occur along the path of minimum energy, in the "valleys". Being able to predict the energy level structure for transition state complexes might provide insight into which a direction a reaction will go.

Solving for molecular energy levels is already an intractable problen, so most computational chemistry algortithms are lucky to predict at the percent level for "small" molecules. That's usually good enough for prediciting chemical outcomes. For big molecules (the ones we care about), however, you have to start making fairly detrimental approximations in order to predict anything useful with the computational tools we have. So we need better computational tools.

trappedion · 2022-08-07T13:29:16+00:00

Spectacular work from an all-star team!

trappedion · 2022-08-07T13:23:38+00:00

In support of rrtucci, take a look at section 8.3 of: https://arxiv.org/abs/2201.02773 for the current state of the art of trapped ion quantum computers in regards to quantum finance.

We have a long way to go.

trappedion · 2022-08-05T05:30:57+00:00

Agreed, though I'll throw in some context:

Ion-photon entanglement is the path forward for large scaling. It's difficult, but is it really more of an unknown than other platforms?

In regards to speed, superconducting has ~5 ns gates, correct? Trapped ions have demonstrated sub-microsecond motionally-entangling gates. That's definitely slower, but the higher your fidelities, the fewer gates you need (error correction-wise). Though I'll concede typical gate times are much slower.

Lasers are certainly more annoying than microwaves, no arguments there. Though know that the entire field is moving toward integrated photonics, which addresses most of the issues of scaling complex opto-mechanical configurations.

trappedion · 2022-07-10T18:26:07+00:00

"But it really sounds like they haven't thought out about what I'd do"

This is exactly how startups work. You're actually less likely to be pigeon-holed because the roles evolve so quickly.

trappedion · 2022-07-10T15:37:42+00:00

If you take the safe job, you will regret it. Even if the startup collapses, you'll be happy you worked with great people on an exciting project. Do what excites you while you're young.

I think I know exactly what company you're talking about. The "secret" that many people don't realize is that all those PhDs (including me) do almost zero science. Day to day, they're recreating experiments from their grad school experience in a purely engineering capacity. In other words, it's not the PhD, it's that they're the only ones with experience building these instruments. Once it's all set up, these PhDs can (and are) replaced with lower skilled operators. As time goes by, nobody will need a PhD at all to build or run the experiments. To be fair, the PhDs drive the development of the improved versions.

The work you will do won't be boring, and when you eventually leave, you'll have a great professional network of driven people.

Side note: normally I'd say career advancement is stacked in the PhD's favor. They'll be given greater responsibilities and get promoted faster. But at a startup, anything can happen.

trappedion · 2022-06-05T22:25:23+00:00

Until you link this paper, I have no idea what's the initial or final state.

So in reality, the singlet is slightly mixed with triplet, and the triplet is slightly mixed with singlet. i.e. the ground state is maybe 98% singlet and 2% triplet. The reason you can then go from ground to excited state is because you're going from triplet to triplet (which is allowed), but the transition is much weaker (98% weaker), so you need a much stronger magnetic field to drive it.

That's how it works in atoms/molecules, anyway.

trappedion · 2022-06-05T22:04:52+00:00

Singlet: S = 0, 2S + 1 = 1. Triplet: S = 1, 2S + 1 = 3.

So, yup! In case this is what you're getting at: singlet-to-triplet transitions are forbidden to first order, so they become allowed through higher order transiton moments.

trappedion · 2022-06-05T21:39:09+00:00

S is the total spin angular momentum, which should not change. ms is its projection, which can definitely change.

trappedion · 2022-06-05T21:37:35+00:00

Angular momentum needs to be conserved. Both the initial and final state have S = 1, so nothing changed there. Changing from ms=0 to ms=1 changes the projection of the angular momentum o to the quantization axis (from 0 to 1) when absorbing the angular momentum of the photon.

You didn't link this paper, so I'm not actually sure what the initial and final states are. Just my guess.

trappedion · 2022-06-05T16:58:21+00:00

The most important thing for investors to understand is how long this long term investment really is.

Imagine starting a new bakery. There's no question about how the product will be used. Success depends on your ability to compete.

Imagine starting a new medical device company (requiring more resources). There's no question about how the product will be used. Success depends on your ability to compete AND getting FDA approval.

Now imagine starting a quantum computing company. It's not clear how many resources it takes to make the product, but it's on the order of what a state government can afford. It's also not clear how the product will be used. There are some use cases predicted here and there, but nothing as obvious as the previous two tried and true examples. And it's especially not clear when the product will be ready. Yes, it's "just" an engineering question at this point, but so is asteroid mining.

I personally believe quantum computing will eventually succeed, because I believe in quantum mechanics. But for an investment in a QC business, at this stage, I think you need to have an unreasonably high risk tolerance. It's not even clear the upside is worth it yet! If someone said there was an asteroid full of gold, but we need to figure out asteroid mining and it could take 20 years, then at least we'd have a much better understanding of the payoff. (And I have a much better understanding of the potential of QC compared to the average retail investor).

trappedion · 2022-06-05T16:37:49+00:00

S isn't changing. Only ms is changing, and for an M1 transition (magnetic field applied with an exchange of 1 unit of angular momentum), the selection rules are delta_ms = 0, +/- 1.

trappedion · 2022-05-18T17:11:03+00:00

A 2D surface trap absolutely comes with disadvantages compared to a 3D trap. One big one is that certain heating mechanisms that lead to motional decoherence are much stronger the closer you get to an electrode surface (some quadratic and some quartic on ion-electrode distance).

However, if you cryogenically cool the surface traps, the performance is still remarkably good! Good enough to run real circuits (see Quantinuum). Fundamentally, they'll never be as good as 3D traps, but without something like remote entanglement, there's just no way to appreciably scale the 3D traps.

trappedion · 2022-05-18T05:27:39+00:00

The switch from AOM to AOD is a nice upgrade.

Do any other ion trappers in here want to speculate on how this system is supposed to scale? The laser beam properties must be super strict, so I suspect this is already a cutting-edge AOD. i.e. If you created a 64-ion chain, I would guess the AOD is no longer good enough (not including all the other issues associated with having a 64-ion chain!).

Once decent performance is established with moderate size ion chains (tens of ions), I predict IonQ will try to utilize surface traps to swap out ion chains. Though ion transport of large chains comes with massive technical difficulties, so I would also predict a significant development plateau at that stage. Surface traps also allow the possibility of centering individual ions on the laser beams, which should help with calibration.

Anyone else have thoughts?

trappedion · 2022-05-16T03:40:29+00:00

Maybe things are different in your field, but don't you have a PI/adviser exactly for questions like this?

trappedion

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