[CQT-467] Add three-qubit gates CCX and CSWAP - #711
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September 8, 2026 08:38
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I added ThreeQubitGate with CCX (alias CCNOT) and CSWAP, a ThreeQubitGateDecomposer into CZ and single-qubit gates, and cQASM v1 export of the Toffoli gate.
The CCX decomposition uses 6 CZ gates, which Shende and Markov (2008) prove is minimal. CSWAP uses 8, but that's an upper bound only: the Fredkin CNOT-cost is still open. Both preserve global phase exactly.