Controlling photon polarisation with a single quantum dot spin

TL;DR

This paper demonstrates the control of photon polarization using a single quantum dot spin within a high-Q cavity, enabling deterministic, spin-dependent polarization rotations crucial for quantum communication and computing.

Contribution

The study introduces a cavity-enhanced spin-photon interface that achieves large, controllable polarization rotations with a single quantum dot, advancing scalable quantum node development.

Findings

Achieved polarization rotations of ±π/2 and π on the Poincaré sphere.

Environmental noise does not limit rotation amplitude but slightly reduces polarization purity.

Controlled spin-induced rotations enable manipulation of photon polarization in most of the Poincaré sphere.

Abstract

In the framework of optical quantum computing and communications, a major objective consists in building receiving nodes that implement conditional operations on incoming photons, using the interaction with a single stationary qubit. In particular, the quest for scalable nodes motivated the development of cavity-enhanced spin-photon interfaces with solid-state emitters. An important challenge remains, however, to produce a stable, controllable, spin-dependant photon state, in a deterministic way. Here we use a pillar-based high-Q cavity, embedding a singly-charged semiconductor quantum dot, to demonstrate the control of giant polarisation rotations induced by a single electron spin. A complete tomography approach is used to deduce the output polarisation Stokes vector, conditioned by a single spin state. We experimentally demonstrate rotation amplitudes such as $\pm \frac{\pi}{2}$ and $\pi$ in the Poincar\'e sphere, as required for applications based on spin-polarisation mapping and spin-mediated photon-photon gates. In agreement with our modeling, we observe that the environmental noise does not limit the amplitude of the spin-induced rotation, yet slightly degrades the polarisation purity of the output states. We find that the polarisation state of the reflected photons can be manipulated in most of the Poincar\'e sphere, through controlled spin-induced rotations, thanks to moderate cavity birefringence and limited noise. This control allows the operation of spin-photon interfaces in various configurations, including at zero or low magnetic fields, which ensures compatibility with key protocols for photonic cluster state generation.