Continuous quantum measurement: inelastic tunnelling suppresses current oscillations

TL;DR

This paper demonstrates that inelastic tunnelling in a charge qubit's detector suppresses coherent oscillations and causes relaxation, highlighting the role of inelastic processes in quantum measurement dynamics.

Contribution

It formally shows that in the sub-Zeno limit, inelastic tunnelling dominates, reducing detector efficiency and inducing decoherence, which was not predicted in previous models.

Findings

Coherent oscillations are suppressed in the sub-Zeno limit.

Inelastic tunnelling reduces detector efficiency and causes relaxation.

Different bias regimes show distinct power spectral behaviors.

Abstract

We study the dynamics of a charge qubit, consisting of a single electron in a double well potential coupled to a point-contact (PC) electrometer, using the quantum trajectories formalism. Contrary to previous predictions, we show formally that, in the sub-Zeno limit, coherent oscillations in the detector output are suppressed, and the dynamics is dominated by inelastic processes in the PC. Furthermore, these reduce the detector efficiency and induce relaxation even when the source-drain bias is zero. This is of practical significance since it means the detector will act as a source of decoherence. Finally, we show that the sub-Zeno dynamics is divided into two regimes: low- and high-bias in which the PC current power spectra show markedly different behaviour.