Three stage decoherence dynamics of electron spin qubits in an optically active quantum dot

TL;DR

This paper reveals that electron spin qubit decoherence in quantum dots involves three distinct stages, including a previously overlooked coherent dephasing process, refining the understanding of decoherence mechanisms in solid-state quantum systems.

Contribution

It demonstrates that decoherence involves an additional coherent dephasing stage, challenging the traditional two-stage phenomenological model for spin qubits in quantum dots.

Findings

Identification of a third decoherence stage involving coherent dephasing.

Observation of non-monotonous relaxation of spin polarization.

Refinement of the decoherence model for electron spin qubits.

Abstract

The control of discrete quantum states in solids and their use for quantum information processing is complicated by the lack of a detailed understanding of the mechanisms responsible for qubit decoherences. For spin qubits in semiconductor quantum dots, phenomenological models of decoherence currently recognize two Basic stages; fast ensemble dephasing due to the coherent precession of spin qubits around nearly static but randomly distributed hyperfine fields and a much slower process of irreversible relaxation of spin qubit polarization due to dynamics of the nuclear spin bath induced by complex many-body interaction effects. We unambiguosly demonstrate that such a view on decoherence is greatly oversimplified; the relaxation of a spin qubit state is determined by three rather than two basic stages. The additional stage corresponds to the effect of coherent dephasing processes that occur in the nuclear spin bath that manifests itself by a relatively fast but incomplete non-monotonous relaxation of the central spin polarization at intermediate timescales. This observation changes our understanding of the electron spin qubit decoherence mechanisms in solid state systems.