An on-chip cross-waveguide QD spin-photon interface and its applications

Quantum dot (QD) systems containing electron spins may hold a role in a future photonic quantum circuit as a means of storing a quantum state in a spin superposition. In general, the spin superposition state maps directly to a photon emitted out of the plane (k_z) with the photon in a polarization superposition. In waveguides, however, this is more difficult: one requires a waveguide mode that is able to transmit both TE_x and TE_y modes in coherent superposition. We have already demonstrated a cross-waveguide design, as shown in Fig 1(a), that converts spin superposition states to a path encoding when the QD is located close to the waveguide centre.