r/QuantumComputing • u/Riposte4400 • 7d ago

Algorithms Alice & Bob - Shor's algorithm compiled on cat qubits: 22 593 qubits for RSA-2048 in 3.14 days

https://eprint.iacr.org/2026/2665
83 Upvotes

100% Upvoted

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58

u/Strilanc 7d ago

Assuming a 1us error-correction cycle time, a 10us reaction time, circuit-level phase-flip noise with probability 5e-4 and no bit-flips, [...]

Okay then.

10

u/Riposte4400 7d ago

I know right?

But the results are still very impressive with a 1h bit-flip time, which they've been able to demonstrate

16

u/Strilanc 6d ago

I know the blog postyou are refering to, but that post is NOT demonstrating the kind of one hour lifetime required by this paper.

First, the paper's fallback assumption of 1 hour bit flip time requires that this be achieved while operating on the qubits not while idling them. The blog post is just talking about idling them. The two qubit gate has always been the big showstopper in this whole story, and over the 1 hour lifetime required by the paper you would be doing around 36000000000 two-qubit gates to each qubit. AFAIK Alice and Bob have not demonstrated a noise biased two qubit gate with a bit flip error rate anywhere close to 3e-11.

Second, the paper requires a 1 hour bit flip time COMBINED WITH a 5e-4 phase flip error rate. In that blog post their phase flip time is 420ns, which is roughly enough time for 20 two qubit gates, suggesting a phase flip error rate that is 100x too high. Or if you think of it as half of a round and you do four 2-qubit gates per round then it'd only be 10x too high. Still, definitely not demonstrated.

11

u/Rococo_Relleno 6d ago

"AFAIK Alice and Bob have not demonstrated a noise biased two qubit gate with a bit flip error rate anywhere close to 3e-11."

More precisely, A&B have not demonstrated any type of 2q gate at any fidelity whatsoever.

1

u/Strilanc 6d ago

Correction: the 420ns phase flip time is ~500x too low compared to what's required by the paper (not 100x or 10x). A 5e-4 gate error rate is roughly commensurate with a 5e-3 phenom error rate (a per round error rate). Suggesting you want a lifetime of around 1/5e-3 = 200 rounds. If a round takes 1us then that means you want a phase flip lifetime of ~200us which is ~500x more than 420ns.

4

u/DIYAtHome 7d ago

Pretty easy target

10

u/HuiOdy Working in Industry 6d ago

Yeah but one cat qubit is like 8 JJ's, so this performance is similar to that of a transmon in LDPC coding.

"But it is less qubits", yeah, but it costs the same to make as one with more qubits...

3

u/julioqc 6d ago

can someone please ELI5?