Robust adiabatic approach to optical spin entangling in coupled quantum dots

TL;DR

This paper demonstrates that an adiabatic, off-resonant laser approach can significantly improve the fidelity of optical spin entangling gates in coupled quantum dots by suppressing decoherence channels, compared to conventional dynamic methods.

Contribution

It introduces an adiabatic scheme for optical spin entangling in quantum dots that reduces decoherence and enhances gate fidelity over traditional dynamic approaches.

Findings

Adiabatic approach achieves gate fidelity of 1% error rate.

Conventional dynamic methods are less suitable for scalable quantum computation.

Predictions are experimentally feasible in the near future.

Abstract

Excitonic transitions offer a possible route to ultrafast optical spin manipulation in coupled nanostructures. We perform here a detailed study of the three principal exciton-mediated decoherence channels for optically-controlled electron spin qubits in coupled quantum dots: radiative decay of the excitonic state, exciton-phonon interactions, and Landau-Zener transitions between laser-dressed states. We consider a scheme to produce an entangling controlled-phase gate on a pair of coupled spins which, in its simplest dynamic form, renders the system subject to fast decoherence rates associated with exciton creation during the gating operation. In contrast, we show that an adiabatic approach employing off-resonant laser excitation allows us to suppress all sources of decoherence simultaneously, significantly increasing the fidelity of operations at only a relatively small gating time cost. We find that controlled-phase gates accurate to one part in 10^2 can realistically be achieved with the adiabatic approach, whereas the conventional dynamic approach does not appear to support a fidelity suitable for scalable quantum computation. Our predictions could be demonstrated experimentally in the near future.