Ultra-compact on-chip optical quantum circuit based on structured Si quantum logic gates

Quantum circuits are common platforms for quantum computing and quantum information processing. However, the sizes of conventional quantum circuits are too large to be suitable for on-chip circuits. We present an intelligent reverse design methodology using a sequential quadratic program (SQP) for designing ultra-compact optical quantum logic gate (QLG) cells on chips. The single-qubit gates, including the Hadamard (H) gate and the Pauli-X gate, are designed whose sizes are 0.75 μm × 1.5 μm and 3.74 μm × 1.15 μm, respectively. Meanwhile, the two-qubit gates, including the controlled-NOT (CNOT) gate and the SWAP gate, are constructed from fundamental cells with footprints of 4.15 μm × 1.9 μm and 3.65 μm × 7.10 μm, respectively. The gates are the currently smallest QLGs reported by far. Furthermore, an optical quantum circuit has been integrated by cascading these logic gates, whose size is 10.18 μm × 4.15 μm, which is about several orders smaller than that of previous optical quantum circuits. It is expected that it can provide a new way to realize large-scale optical quantum circuits via the inverse design method.