Highly efficient spin qubit to photon interface assisted by a photonic crystal cavity

Abstract

Interfacing semiconductor with photonic qubits plays an important role in quantum networks. We model a photon to spin qubit interface based on an optically active gate-defined quantum dot embedded in a two-dimensional photonic crystal cavity constraining its emission profile with a low enough quality factor for emission wavelength tuning. By matching the cavity-mode k-vector and reciprocal lattice of the crystal, vertical emission is obtained. A reflector below the cavity increases not only the light extraction efficiency, but also tailors the extracted beam profile to match that of a single mode fiber, into which photons emitted by the quantum dot are coupled with a probability above 50%. The efficiency is primarily limited by metal electrode absorption. In addition to trapping the exciton, the electrode system embedded inside the cavity allows trapping, manipulation and readout of a pair of electrons encoding a spin qubit in a singlet-triplet configuration, whose quantum state can be transferred to and from the exciton by utilizing an existing protocol. Experimental realization of these devices is currently in progress with first results in regard to fabrication also reported.