Full-counting statistics and quantum information of dispersive readout with a squeezed environment

TL;DR

This paper develops a comprehensive full-counting-statistics framework for dispersive quantum readout with squeezed environments, revealing exponential enhancement of measurement information and robustness against nonlinearity, advancing continuous quantum measurement techniques.

Contribution

It introduces a novel full-counting-statistics approach for dispersive readout, enabling direct calculation of cumulants and analysis of measurement information in nonlinear quantum systems.

Findings

Fisher information exponentially increases with squeezing parameter.

The framework approaches the quantum Fisher information limit.

Robustness of measurement information against residual nonlinearity.

Abstract

Motivated by the importance of dispersive readout in quantum technology, we study a prototypical dispersive readout setup that is probed by a squeezed vacuum in a time-reversal-symmetric fashion. To this end, we develop a full-counting-statistics framework for dispersive readout and analyze its measurement information, accompanied by a generalized mean-field approach suitable to deal with non-unitary dynamics. Distinct from conventional input-output theory, our full-counting-statistics approach enables the direct calculation of arbitrary-order cumulants for the measured cumulative (i.e., time-integrated) photonic distribution while maintaining applicability to nonlinear systems. The corresponding Fisher information exhibits an exponential dependence on the squeezing parameter and a robustness against residual nonlinearity, which can even approach the quantum Fisher information, setting an upper limit. This work introduces a conceptually streamlined and computationally efficient framework for continuous quantum measurements, making it well suited for widespread adoption in quantum technologies.