Coherence limitations in the optical control of the singlet-triplet qubit in a quantum dot molecule

TL;DR

This paper investigates the limitations of optical control in a singlet-triplet qubit within quantum dot molecules, analyzing control schemes, imperfections, and decoherence effects to optimize quantum operations.

Contribution

It provides a detailed quantitative analysis of control imperfections and decoherence in optical qubit manipulation, highlighting trade-offs and optimal conditions.

Findings

Non-adiabatic evolution causes control errors.

Spectral selectivity limits fidelity.

Decoherence from phonons and radiative processes impacts performance.

Abstract

We analyze the optically driven dynamics of a qubit implemented on a singlet-triplet subspace of two-electron states in a self-assembled quantum dot molecule. We study two possible control schemes based on the coupling to an excited (four-particle) state either by two spectrally separated laser pulses or by a single spectrally broad pulse. We quantitatively characterize the imperfections of the qubit operation resulting from non-adiabatic evolution and from limited spectral selectivity in a real system, as compared to the ideal adiabatic Raman transfer of occupation in the $\Lambda$-system. Next, we study the effects of decoherence induced by the coupling to the phonons of the surrounding crystal lattice and by radiative recombination. As a result, we are able to identify the optimization trade-offs between different sources of errors and indicate the most favorable conditions for quantum control of the singlet-triplet qubit in the two optical control schemes.