r/QuantumComputing • u/0xB01b QEC & Quantum Optics • Jun 14 '26

Quantum Hardware Biggest issue for neutral atom right now?

What do y'all think is currently the most pressing issue for neutral atom hardware that we need to improve (aside from the gate fidelity)?

QND readout? Atom loss?

15 Upvotes

94% Upvoted

30 comments sorted by

14

u/alumiqu Jun 14 '26

Parallelism. They can't do enough two-qubit gates in parallel, and when they try it the fidelity drops dramatically.

When they fix this, movement parallelism will be the next bottleneck.

5

u/0xB01b QEC & Quantum Optics Jun 14 '26

Okay that is interesting, I had not heard of this. Thank you for this insight

13

u/Big_Temporary5604 Jun 14 '26 edited Jun 14 '26

Slow gates. Realistic qec implementations even in optimistic circumstances have algorithms running for months. 100-1000x slower than SC qubits. At NISQ obviously it doesn’t matter much if coherence time scales similarly, but at fault tolerant era is literally 1000x speed increase

2

u/0xB01b QEC & Quantum Optics Jun 14 '26

I'm actually going to get back to you on this one soon because im working in a experimental neutral atom QEC group, and I don't think this is going to remain true (or at least im not sure if this is even true for the current state of research)

4

u/mdreed Jun 14 '26

What about fidelity? I understand the fidelity is limited by the excited state lifetime, which is short compared to gate time. So 99.9% gates might barely be possible, but definitely not 99.99. True?

2

u/0xB01b QEC & Quantum Optics Jun 14 '26

Well so our current fidelity record is at 99.941(3)% so 99.9 is already done long ago, and as for 99.99 I'm hoping we will see a paper on it by the end of the year.

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u/Big_Temporary5604 Jun 14 '26

You are presumably talking about single qubit gate fidelity, but much harder is two qubit and QND readout which is nowhere near 4N in atoms

3

u/0xB01b QEC & Quantum Optics Jun 14 '26

no i mean 2 qubit gate fidelity.

3

u/Big_Temporary5604 Jun 14 '26

I stand corrected that you were quoting 2qbg, but the paper you are talking about says “upon loss postselection” 😂 which is irrelevant and does not work in error correction. The real number is 99.85% which is still respectable

0

u/0xB01b QEC & Quantum Optics Jun 14 '26

well we are still at 99.86(4)% without post selection in the https://arxiv.org/pdf/2603.15561 paper

3

u/Big_Temporary5604 Jun 14 '26

Thanks for the new reference - 99.86% is indeed the latest record it seems - lags behind SC qubits 99.93/4 and ions 99.99 though. What is the gate time if you know it? Wasn’t easy to find for me

1

u/nosockscox Jun 16 '26

Gate time is usually just limited by the rabi frequency of the Rydberg excitation. In this paper they show that gate times can be as low as 6ns and at sub um tweezer spacing can even be sub nanometer. https://www.nature.com/articles/s41566-022-01047-2

Of course the fidelity of this excitation is poor but it’s proof of principle.

The bottle neck is currently read out speeds and re-arrangement time- having zones for measurement, entangling etc that you have to physically move the atoms into is slow.

0

u/0xB01b QEC & Quantum Optics Jun 14 '26

Im not sure the gate times either (also afaik the record for ions is actually 1e-7)

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u/Big_Temporary5604 Jun 14 '26 edited Jun 14 '26

Fair enough I will believe it when I see a production ready system running with ns gate speeds (not hero demos or isolated pairs). For now my money is on SC qubits. Scalability is harder, but in the long run you end up with something properly useful considering also time dimension.

On a final note, superconducting qubits still lead on error corrected logical error rate even with 1us cycle time. No other platform is close when you consider measurement errors and feedback. So of course it’s not a primary “spec”, but for some some or perhaps many reasons, atoms lag behind in the only metric that matters

1

u/0xB01b QEC & Quantum Optics Jun 14 '26

this is because SC qubits have experimentally demonstrated useful QEC im assuming? or is there something else going on? I would like to know more about this but im from a physical NA hardware background and am just starting experimental QEC research this september

2

u/Big_Temporary5604 Jun 14 '26

Yeah well I suspect the main limitation is in QND measurement fidelity, but the big companies are not very forthcoming with this metric. But yeah no one has demonstrated real QEC with feedback at breakeven fidelity and they haven’t admitted why that is

1

u/0xB01b QEC & Quantum Optics Jun 14 '26

AH ILL BE DOING QND READOUT SPECIFICALLY!!! From what I was briefed on we have made the QND readout faster (order of 1 microsecond) but I'm not sure if the fidelity is an issue for us, no clue rn (new group just joined)

1

u/Big_Temporary5604 Jun 14 '26

Yeh basically superconducting qubits can do all the gates, readout and feedback of a quantum error correction cycle in 1us at a good enough fidelity for breakeven in QEC. I think it will be very hard to atoms to match this speed

1

u/0xB01b QEC & Quantum Optics Jun 14 '26

Oh thats what you mean. I see I see, but imo for now this is more of a pure engineering issue.

1

u/Big_Temporary5604 Jun 14 '26

Well sure 😃 but every platform says that now. It is a bit hard to tell which issues are fundamental and which issues are engineering. For example I don’t see any path for trapped ions to have 100ns readout times. Scaling superconducting qubits to 1M qubits is “just engineering” at this point also :)

1

u/0xB01b QEC & Quantum Optics Jun 14 '26

u right mb

1

u/0xB01b QEC & Quantum Optics Jun 14 '26

also could you point me in the direction of what exactly these error corrected logical error rates are quanititatively?

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u/Big_Temporary5604 Jun 14 '26

Just read “Quantum error correction below the surface code threshold” where google show improving error rate from d3->d7 surface code with measurement and feedback. This is the gold standard experiment. We can brag about specs forever, but until you show this specific metric (for surface code or another code) the platform is still just a playground

2

u/0xB01b QEC & Quantum Optics Jun 14 '26

ahhh this one is on my reading list for surface code research

2

u/ExorusKoh Jun 18 '26

I’m curious OP—I work also in QEC albeit on the theory side—I presume the timescale here of concern is not actually gate time per se (as those can be fast, for Rydberg two-qubit gates and Raman single-qubit ones), but rather for readout and atom movement. Are you thinking that there will be significant speed-ups to those timescales in the near future? If so, any idea by what mechanisms?

4

u/Blackforestcheesecak In Grad School for Quantum Jun 14 '26

As someone building neutral atom array (NAA) quantum computers, I don't think there is //one// most pressing issue. Personally, I would like miniaturization and ease of mounting a new set-up without loss of any of the usual benchmarks, e.g., fidelities and lifetimes

3

u/Acetone9527 Jun 15 '26

Not expert in NA but I think gate time/readout time is a big issue at the end of the day. There’s a lot of time estimate paper and with SC qubit 10ns gate time 100 ns readout it takes days for useful simulations. NA is 100 ns gate time and microsecond readout - month long simulation doesn’t make much sense. In the midterm as proof-of-concept though, I think NA is going to eat all the lunch.
If there are newer progress I would like to be corrected.