An efficient singlet-triplet spin qubit to fiber interface assisted by a photonic crystal cavity

We introduce a novel optical interface between a singlet-triplet spin qubit and a photonic qubit which would offer new prospects for future quantum communication applications. The interface is based on a 220 nm thick GaAs/Al-GaAs heterostructure membrane and features a gate-defined singlet-triplet qubit, a gate-defined optically active quantum dot, a photonic crystal cavity and a bot-tom gold reflector. All essential components can be lithographically defined and deterministically fabricated, which greatly increases the scalability of on-chip in-tegration. According to our FDTD simulations, the interface provides an overall coupling efficiency of 28.7% into a free space Gaussian beam, assuming an SiO2 interlayer filling the space between the reflector and the membrane. The performance can be further increased to 48.5% by undercutting this SiO2 interlayer below the photonic crystal.