Multi-spin errors in the optical control of a spin quantum memory

TL;DR

This paper investigates multi-spin errors in optical quantum memory systems based on charged quantum dots in a cavity, proposing methods to suppress errors and achieve high-fidelity quantum gates within decoherence times.

Contribution

It introduces a technique to suppress multi-spin interactions in quantum dot arrays, enabling high-fidelity detuning-based quantum gates.

Findings

Multi-spin interactions cause errors in quantum gates.

Local control of exciton energy suppresses multi-spin errors.

High-fidelity conditional phase shift gates are achievable.

Abstract

We study a quantum memory composed of an array of charged quantum dots embedded in a planar cavity. Optically excited polaritons, i.e. exciton-cavity mixed states, interact with the electron spins in the dots. Linearly polarized excitation induces two-spin and multi-spin interactions. We discuss how the multi-spin interaction terms, which represent a source of errors for two-qubit quantum gates, can be suppressed using local control of the exciton energy. We show that using detuning conditional phase shift gates with high fidelity can be obtained. The cavity provides long-range spin coupling and the resulting gate operation time is shorter than the spin decoherence time.