The article by CQP Researchers Dr Jonathan Matthews, Beccie Whittaker, Professor Jeremy O'Brien and Dr Peter Turner; discusses how generating and characterizing randomness is fundamentally important in both classical and quantum information science.

They report on the experimental demonstration of ensembles of pseudorandom optical processes comprising what are known as t-designs, showing that in practical scenarios, certain finite ensembles of two-mode transformations—1- and 2-designs—are indistinguishable from truly random operations for 1- and 2-photon quantum interference, but they fail to mimic randomness for 2- and 3-photon cases, respectively.

Making use of the fact that t-photon behaviour is governed by degree-2t polynomials (in the parameters of the optical process), to experimentally verify the ensembles' behaviour for complete bases of polynomials, has ensured that average outputs will be uniform for arbitrary configurations. It is in this sense that a t-design is deemed to be a potentially useful pseudorandom resource.

You can read the whole article here.