Inverse-designed universal quantum logic gates for super-compact quantum circuits

Abstract Integrated quantum photonic circuits are a promising approach to realizing future quantum information processing. To achieve large-scale quantum photonic circuits, as many quantum logic gates as possible are expected to be integrated on chips. This requires quantum logic gates to be as small as possible. Here, we report the implementation of super-compact universal quantum logic gates on silicon photonic chips by inverse design. The sizes for the fabricated optical controlled-NOT gate and single-qubit gates (Hadamard gate) on the chip are about one vacuum wavelength, which are the smallest optical quantum gates ever verified in the world. The quantum circuit by these cascaded fundamental gates is shrunk several orders compared to those previous quantum photonic circuits that perform arbitrary quantum processing. Our study paves the way for the realization of large-scale quantum photonic chips with integrated sources for practical quantum information processes.