Boson Sampling in the Frequency Domain

We present a scheme to perform Boson sampling using frequency modes that results in significantly reduced losses and experimental complexity as compared to existing spatial mode implementations. Boson sampling is computationally intractable on a classical computer but can be efficiently performed using a linear optical network. Our scheme uses Bragg-scattering four wave mixing (BS-FWM), a third-order nonlinear process to achieve coherent interaction between a large number of frequency modes mediated by strong classical pumps and has distinct advantages over spatial mode implementations. While spatial beam splitters couple only nearest neighbors, it is straightforward to create highly delocalized non-nearest neighbor couplings using BS-FWM, leading to complex unitary interaction with fewer resources. Moreover, the interaction takes place in a single nonlinear fiber, resulting in fixed loss independent of the number of modes. To demonstrate experimental feasibility, we show Hong-Ou-Mandel interference between correlated photons of distinct frequencies, using BS-FWM as a frequency beam splitter. We believe our scheme addresses multiple challenges to scale Boson Sampling to the regime of 20-30 photons, which could provide confirmation for quantum speedup over classical simulations.