Case Studies on oqft.com

Choosing an Error Target for a 2048-Qubit OQFT, Each Tenfold Tightening Costs 24 to 32 Layers

Fri, 13 Nov 2026 00:00:00 +0000

OQFT asks for one number besides the register size: the error target, --eps. It’s the average squared error you’re willing to accept over all inputs. Pick it too loose and Shor’s algorithm misses more often. Pick it too tight and you pay in depth. This case study puts numbers on that trade for a 2,048-qubit register, the size a 2048-bit RSA key calls for.

We ran oqft stats -n 2048 at four targets, from 0.1 down to 0.0001, and recorded the block width OQFT chose for each.

How Block Width Sets the Error of an Optimistic QFT, Measured on 16 Qubits

Fri, 13 Nov 2026 00:00:00 +0000

The block width is the one knob inside an optimistic QFT. Narrow blocks make a shallow circuit that fails often. Wide blocks fail rarely but cost more depth. OQFT normally picks the width for you from the error target, but on a register small enough to simulate you can force it with --block-width and watch what happens.

We took a 16-qubit register, forced every width from 2 to 8, and ran 300 random inputs through the simulator for each, with the same seed every time so the run can be repeated. For each input oqft check measured the squared error against the exact QFT, and flagged any above 0.1.

OQFT Depth Crossover, the Optimistic QFT Beats the Textbook Circuit From 68 Qubits On

Fri, 13 Nov 2026 00:00:00 +0000

The optimistic QFT is built for big registers. Everyone working with it knows that. The less obvious question is where “big” starts, because below some size the textbook circuit is simply shallower, and a compiler that swaps in OQFT everywhere would make small circuits worse.

So we ran oqft stats at an error target of 0.01 for every register size from 32 to 80 qubits, plus a few larger ones, and wrote down depth and gate count for both circuits. Depth counts every gate as one layer, with gates on separate qubits sharing a layer.