Frequency-Encoded quantum multi-photon interference devices
Optical quantum computing and quantum simulation rely on multi-photon interference effects, between many photons in a larger number of optical paths or modes. In particular in Gaussian Boson Sampling protocols, single-mode squeezed states are input to an optical circuit implementing a transformation on the modes, which creates a complex multi-mode squeezed state. Sampling from such a state with single photon detectors is thought to be an intractable problem to simulate with classical computers, and has useful applications, for instance in calculating molecular vibronic spectra and in identifying densely connected sub-graphs of a network. This motivates building quantum-optical devices to implement Gaussian Boson Sampling. However, it is resource intensive to create a usefully large state using many separate squeezed sources and a circuit, and very technically challenging to avoid photon loss and to maintain interferometric stability. Here, I propose to carry out Gaussian Boson Sampling and related experiments by directly generating multi-mode squeezed states encoded in frequency, from a single source with reconfigurable frequency correlations. Using frequency channels to represent the modes is very compact because they can all propagate along the same spatial path, and this also ensures interferometric stability. Directly generating the desired state will avoid having the photons propagate through a lossy circuit, allowing scaling to higher photon numbers, and frequency encoding will make large numbers of modes readily available, surpassing the state-of-the-art in spatially-encoded circuits.