Programmable Interference between Two Microwave Quantum Memories

Abstract

Interference experiments provide a simple yet powerful tool to unravel fundamental features of quantum physics. Here we engineer a driven, time-dependent bilinear coupling that can be tuned to implement a robust 50∶50 beam splitter between stationary states stored in two superconducting cavities in a three-dimensional architecture. With this, we realize high-contrast Hong-Ou-Mandel interference between two spectrally detuned stationary modes. We demonstrate that this coupling provides an efficient method for measuring the quantum state overlap between arbitrary states of the two cavities. Finally, we showcase concatenated beam splitters and differential phase shifters to implement cascaded Mach-Zehnder interferometers, which can control the signature of the two-photon interference on demand. Our results pave the way toward implementation of scalable boson sampling, the application of linear optical quantum computing protocols in the microwave domain, and quantum algorithms between long-lived bosonic memories.