Coherent Optical Control of a Quantum-Dot Spin-Qubit in a Waveguide-Based Spin-Photon Interface

Spin-photon interfaces based on an (In,Ga)As quantum dot coupled to a waveguide are a promising avenue toward scalable quantum information processing, but coherent control of the spin state is challenging, because of the complicated near-to-far-field polarization transformation induced by the waveguide. The authors search for a particular polarization of light that excites a circular dipole in the quantum dot, and use this polarization for the coherent control of an electron's spin. They obtain a coherence time of 2.2 ns, comparable to the typical value in bulk media. The authors' method for polarization-controlled excitation can be readily applied to other nanophotonic structures, too.