Strong non-reciprocal and non-linear transport of photons mediated by a single quantum emitter

Reciprocity and linearity are the most basic and intuitive properties of light and breaking them via a coherent light-matter interaction is of great interest in fundamental physics and applications. Here, we present a system showing both a highly non-reciprocal and non-linear response using a semiconductor quantum dot in a tunable microcavity [1]. Non-reciprocity, the dependence of transmission on the propagation direction, occurs by chirally coupling photons to a quantum dot in a one-sided, polarisation-degenerate cavity and tuning the coupling strength between the cavity and the quantum dot to the critical point. In our experiment, transmission of light in the forward direction is suppressed by a factor of 7 compared to the backward direction. The “atom-like” energy structure of a quantum dot naturally leads to non-linearity at the single-photon level with a saturation power of around 240 pW. Furthermore, we show how the tunable nature of the open microcavity enables its implementation as a diode for single-photons, surpassing any other reported quantum system with respect to non-reciprocal transmission.

[1] N. Tomm et al., arXiv:2007.12654