Interfacing a quantum dot spin with a photonic circuit

TL;DR

This paper presents a method to interface quantum dot spins with photonic circuits by mapping spin states to path-encoded photons using orthogonal nanowires, advancing scalable quantum photonic networks.

Contribution

It introduces a novel on-chip spin-photon interface using orthogonal nanowires, enabling scalable integration of quantum dot spins with photonic circuits.

Findings

Spin states are mapped to path-encoded photons in nanowires.

Circular polarisation states are directly mapped to orthogonal nanowires.

The mapping efficiency depends on the quantum dot's nano-positioning.

Abstract

A scalable optical quantum information processor is likely to be a waveguide circuit with integrated sources, detectors, and either deterministic quantum-logic or quantum memory elements. With microsecond coherence times, ultrafast coherent control, and lifetime-limited transitions, semiconductor quantum-dot spins are a natural choice for the static qubits. However their integration with flying photonic qubits requires an on-chip spin-photon interface, which presents a fundamental problem: the spin-state is measured and controlled via circularly-polarised photons, but waveguides support only linear polarisation. We demonstrate here a solution based on two orthogonal photonic nanowires, in which the spin-state is mapped to a path-encoded photon, thus providing a blue-print for a scalable spin-photon network. Furthermore, for some devices we observe that the circular polarisation state is directly mapped to orthogonal nanowires. This result, which is physically surprising for a non-chiral structure, is shown to be related to the nano-positioning of the quantum-dot with respect to the photonic circuit.