Simulating a 12-qubit circuit: measured classical baseline

Reference case

Classical simulation of this circuit takes 14 milliseconds on a laptop CPU. Running it on a fault-tolerant quantum computer would need thousands of physical qubits and would not be faster.

What kind of evidence this is

The classical side of this assessment is a real measurement taken on a named machine on a stated date, not an estimate. Everything on the quantum side is modelled.

This is a reference case published by KetQat. It is not a customer's production evidence and it supports no claim about quantum advantage.

Technically feasible under these assumptions

under the Conservative assumptions

Under this model the computation needs 10,530 physical qubits and 0.000120 s at code distance 9. The computation is technically feasible under this model, but no economic conclusion can be made because no quantum machine-cost assumption was supplied. A surface-code cycle below 1.20e+5 ns would be required to beat the supplied classical runtime.

What is actually stopping this

Magic-state throughput

The binding constraint is magic-state throughput, not logical-qubit capacity: the runtime is set by how fast distilled states arrive rather than by the depth of the logical circuit.

Threshold to cross: below 120,000 nsCycle time needed to beat the classical baseline
Economic conclusion: Not justifiedInsufficient evidence. The missing input is named below.
Evidence confidence: MEDIUM
Kinds of claim, not an average of them.
Largest sensitivity: physical error rate21.2× range in total physical qubits

What to measure next

State the physical qubit capacity of the target device, with a source and a date.
State a quantum machine-cost assumption, even a hypothetical one, so the economic thresholds become computable.
Characterize magic-state factory throughput on the target architecture: it, not logical-qubit count, sets the runtime here.

What is missing

The physical qubit capacity of the device under consideration. Without it, 'does it fit' has no answer.
A dated observation of a real device meeting these physical error rate and cycle time parameters.
A quantum cost model: what a machine-second, or a physical-qubit-second, is assumed to cost, and on whose authority.

What it would take

Total machine: 10,530physical qubits
Runtime: 1.200e-4s
Code distance: 9
Factory share: 46%

Every figure, with its evidence class, assumptions and sensitivity, is under scenarios and evidence.

Can anyone else reproduce this?

Yes. The bundle carries the inputs, the assumptions and the conclusions under one hash, and ketqat-engine intelligence verify recomputes the decisions from those inputs rather than trusting them.

0befaaf67793ece41ed346846774aa8f0dd2ac42b0fd8a9582509b09383fe06d

Download the bundle

Under different assumptions

Resource requirements and threshold conditions for each set of assumptions. No aggregate row is produced: No aggregate row is produced. Scenarios differ in their assumptions, and a mean of results computed under different assumptions is a number none of the models predicts, carrying the apparent authority of all of them. Each row is read on its own terms.
Scenario	Logical qubitsPatches occupied, including routing space.	Total physical qubitsAlgorithm, routing and factory together.	Runtime (s)Under whichever limiter binds.	Code distanceSmallest odd distance meeting the budget.	Factory shareFraction of the machine that is the magic-state factory.	Logical errorAchieved probability of any logical error.	Required cycle (ns)Slowest cycle meeting the target or beating classical.	Required throughputMagic states per second for the runtime target.	EconomicRefused unless a baseline and a cost model both exist.	EvidenceStrength of the inputs behind the row.
ConservativeCONSERVATIVE · revision 1 Technically feasible under these assumptions	35	10,530	1.200e-4	9	46%	0.007	120,000	833.3333	Insufficient evidence	MEDIUM
BaseBASE · revision 1 Technically feasible under these assumptions	35	3,250	1.200e-4	5	46%	0.0029	120,000	833.3333	Insufficient evidence	MEDIUM
OptimisticOPTIMISTIC · revision 1 Technically feasible under these assumptions	35	900	2.400e-5	3	30%	2.880e-4	120,000	833.3333	Insufficient evidence	MEDIUM

How the inputs were obtained

Classical runtime is the measured minimum of five repeats at 12 qubits: 0.0144 s.
Logical counts are derived by parsing the same circuit that was simulated, so both sides describe one workload.

Limitations

A 12-qubit circuit is trivially simulable. This case exists to show a measured comparison and an honest negative result, not to suggest the workload was ever a candidate for quantum computation.
Resource estimates are modelled, not measured. No device was run.
The logical-error prefactor is fitted and its provenance is weak; the alternative published value is reported as model sensitivity on every estimate.
The magic-state factory footprint and throughput are models of the standard construction, not published or measured figures.
The error budget is allocated across the algorithm's own logical qubits; routing patches are charged for space but not against the budget.
One QEC scheme is modelled. Other codes, other layouts, and other hardware modalities are out of scope here.
Nothing in this bundle predicts when any device will meet any condition it states.