Distillation of Indistinguishable Photons

A reliable source of identical (indistinguishable) photons is a prerequisite for exploiting interference effects, which is a necessary component for linear optical based quantum computing, and applications thereof such as Boson sampling. Generally speaking, the degree of distinguishability will determine the efficacy of the particular approach, for example by limiting the fidelity of constructed resource states, or reducing the complexity of an optical circuits output distribution. It is therefore of great practical relevance to engineer heralded sources of highly pure and indistinguishable photons. Inspired by magic state distillation, we present a protocol using standard linear optics which can be used to increase the indistinguishability of a photon source, to arbitrary accuracy. In particular, in the asymptotic limit of small error $\epsilon$, to reduce the error to $\epsilon' < \epsilon$ requires $O((\epsilon/\epsilon')^2)$ photons. We demonstrate the scheme is robust to detection and control errors in the optical components, and discuss the effect of other error sources.