Purcell-Enhanced, Directional Light-Matter Interaction in a Waveguide-Coupled Nanocavity

TL;DR

This paper demonstrates a tunable, spin-dependent, directional photon coupling in a waveguide-coupled nanocavity with quantum dots, achieving high Purcell enhancement and contrast, and models the system's behavior for potential nanophotonic circuit applications.

Contribution

It introduces a novel electrically tunable nanocavity system that enables highly directional, spin-dependent photon emission with enhanced Purcell effect, surpassing previous waveguide-only systems.

Findings

Achieved Purcell factor of 10.8±0.7 and directional contrast of 88±1%.

Demonstrated electrical tuning of emission contrast from 2% to 96%.

Developed models explaining the system's directionality and asymmetry.

Abstract

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 (${10.8\pm0.7}$) and peak directional contrast (${88\pm1\%}$), 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.