Non-Markovian dynamics and noise characteristics in continuous measurement of a solid-state charge qubit

TL;DR

This paper explores how non-Markovian effects influence the dynamics and noise characteristics of continuous charge qubit measurement, revealing potential improvements in measurement efficiency beyond traditional limits.

Contribution

It demonstrates that non-Markovian memory effects can enhance detector signal-to-noise ratio, surpassing the standard quantum measurement bound.

Findings

Non-Markovian backflow affects qubit relaxation and dephasing.

Memory effects can increase signal-to-noise ratio beyond 4.

Violation of the Korotkov-Averin bound observed.

Abstract

We investigate the non-Markovian characteristics in continuous measurement of a charge qubit by a quantum point contact. The backflow of information from the reservoir to the system in the non-Markovian domain gives rise to strikingly different qubit relaxation and dephasing in comparison with the Markovian case. The intriguing non-Markovian dynamics is found to have a direct impact on the output noise feature of the detector. Unambiguously, we observe that the non-Markovian memory effect results in an enhancement of the signal-to-noise ratio, which can even exceed the upper limit of ``4'', leading thus to the violation of the Korotkov-Averin bound in quantum measurement. Our study thus may open new possibilities to improve detector's measurement efficiency in a direct and transparent way.