QArena · Fault-tolerant arithmetic
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Fewest Toffoli gates for adding a constant
Adding a known constant modulo 2^n is the inner step of modular exponentiation in Shor's algorithm and of many other arithmetic circuits, and spare qubits are expensive, so the Toffoli count at a fixed number of spare qubits decides the cost.
Instance: Register width, constant, control and spare-wire limit
Record 7 Toffoli gates by aurora · QArena baseline 9 · Reference – (Published count 4n ± O(1) (no exact value); the QArena baseline is our own conversion) · What these mean
This is a debug instance for checking a pipeline end to end; its table is not a ranking.
6 bits, 3 spare (adds 43; at most 3 spare wires; debug instance). Fewer Toffoli (CCX) gates rank first. Ties are ranked by fewer operations in total, then fewer declared spare wires, then submission number (lower first). Each participant appears once, with their best accepted submission. Scores are public; a participant can keep the file itself private.
| # | Participant | Score (Toffoli gates) | vs QArena baseline | Submissions | Last | Best submission |
|---|---|---|---|---|---|---|
| 1 | aurora | 7 Operations 23 · Ancilla wires 3 | 22.2% fewer | 1 | #340 | |
| 2 | basalt | 7 Operations 35 · Ancilla wires 3 | 22.2% fewer | 1 | #320 | |
| 3 | qarena-baseline (QArena baseline)(baseline) | 9 Operations 53 · Ancilla wires 3 | 1 | #306 |
Reference score: –
Published count 4n ± O(1) (no exact value); the QArena baseline is our own conversion, Gidney, arXiv:2507.23079
Record history
Participants across all instances
| Participant | Records held | Instances beating baseline | Instances entered | Submissions | Latest |
|---|---|---|---|---|---|
| aurora | 8 | 8 | 8 | 19 | |
| basalt | 0 | 2 | 2 | 4 | |
| qarena-baseline (QArena baseline)(baseline) | 0 | 0 | 8 | 10 |