Quantum correlation of light scattered by disordered media

We study theoretically how multiple scattering of light in a disordered medium can spontaneously generate quantum correlations. In particular we focus on the case where the input state is Gaussian and characterize the correlations between two arbitrary output modes. As there is not a single all-inclusive measure of correlation, we characterise the output correlations with three measures: intensity fluctuations, entanglement, and quantum discord. We find that, while a coherent input state can not produce quantum correlations, any other Gaussian input will produce them in one form or another. This includes input states that are usually regarded as more classical than coherent ones, such as thermal states, which will produce a non-zero quantum discordWe are grateful to M. Paternostro, D. Browne, and M. Williamson for insightful discussions. JA acknowledges support by EPSRC (EP/M009165/1). JB acknowledges support from the Leverhulme Trust’s Philip Leverhulme Prize. IS acknowledges support from EPSRC (EP/L015331/1) through the Centre of Doctoral Training in Metamaterials (XM2)