Purcell-enhanced, directional light–matter interaction in a waveguide-coupled nanocavity

We demonstrate electrically tunable, spin-dependent, directional coupling of single photons by embedding quantum dots (QDs) in a waveguide-coupled nanocavity. The directional behavior arises from direction-dependent interference between two cavity modes when coupled to the device waveguides. The small mode volume cavity enables simultaneous Purcell enhancement (10.8 ± 0.7) and peak directional contrast (88 ± 1%), exceeding current state-of-the-art waveguide-only systems. We also present a scattering matrix model for the transmission through this structure, alongside a quantum trajectory-based model for predicting the system’s directionality, which we use to explain the observed asymmetry in directional contrast seen in QD devices. Furthermore, the nanocavity enables wide-range electrical tuning of the emitter’s directional contrast. We present results showing precise tuning of a QD emission line from a directional contrast of 2% to 96%. In combination, these characteristics make this cavity-waveguide approach promising for use as a building block in directional nanophotonic circuits.