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

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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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sub> ) 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> 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.