Title: General protocols for the efficient distillation of indistinguishable photons

Abstract: Highly pure and indistinguishable photons are a prerequisite for use in quantum information processing. We introduce protocols for the distillation of indistinguishable photons that offer a significant improvement over previous work, reducing distinguishability error rates by a factor of $n$, with resource requirements scaling linearly in $n$. We present the protocols, based on the discrete Fourier transform, Hadamard (Sylvester) matrices, and more general Fourier transforms on finite abelian groups, then give both analytical and numerical results regarding their performance. We observe that the same symmetry properties governing suppression laws are instrumental in understanding the behavior of these distillation protocols. We also prove that for the $n$-photon discrete Fourier transform, the suppression laws are exactly characterized by the well-known Zero Transmission Law based on permutation symmetry if and only if $n$ is a prime power.