Retrieving qubit information despite decoherence

TL;DR

This paper demonstrates that, under certain symmetry conditions, information about a qubit's initial state can be retrieved from its long-term behavior despite decoherence caused by telegraph noise.

Contribution

It introduces a method to recover qubit information from persistent currents and occupations even in the presence of decoherence due to telegraph noise.

Findings

Partial decoherence allows information retrieval at long times.

Flux dependence encodes the initial quantum state.

Small deviations lead to slow exponential decay with measurable signatures.

Abstract

The time evolution of a qubit, consisting of two single-level quantum dots, is studied in the presence of telegraph noise. The dots are connected by two tunneling paths, with an Aharonov-Bohm flux enclosed between them. Under special symmetry conditions, which can be achieved by tuning gate voltages, there develops partial decoherence: at long times, the off-diagonal element of the reduced density matrix (in the basis of the two dot states) approaches a non-zero value, generating a circulating current around the loop. The flux dependence of this current contains full information on the initial quantum state of the qubit, even at infinite time. Small deviations from this symmetry yield a very slow exponential decay towards the fully-decoherent limit. However, the amplitudes of this decay also contain the full information on the initial qubit state, measurable either via the current or via the occupations of the qubit dots.