Filter-free single-photon quantum dot resonance fluorescence in an integrated cavity-waveguide device

Abstract

Semiconductor quantum dots embedded in micropillar cavities are excellent emitters of single photons when pumped resonantly. Often, the same spatial mode is used to both resonantly excite a quantum-dot state and to collect the emitted single photons, requiring cross polarization to reduce the uncoupled scattered laser light. This inherently reduces the source brightness to 50%. Critically, for some quantum applications the total efficiency from generation to detection must be over 50%. Here, we demonstrate a resonant-excitation approach to creating single photons that is free of any cross polarization, and in fact any filtering whatsoever. It potentially increases single-photon rates and collection efficiencies, and simplifies operation. This integrated device allows us to resonantly excite single quantum-dot states in several cavities in the plane of the device using connected waveguides, while the cavity-enhanced single-photon fluorescence is directed vertically (off-chip) in a Gaussian mode. We expect this design to be a prototype for larger chip-scale quantum photonics.