Adiabatic Elimination of Gaussian Subsystems from Quantum Dynamics under Continuous Measurement

TL;DR

This paper introduces a method for adiabatic elimination of Gaussian bosonic transducers in quantum systems under continuous measurement, improving readout fidelity even at finite temperatures.

Contribution

It develops a general adiabatic elimination technique for Gaussian bosonic transducers, including finite temperature effects, applicable to various quantum measurement setups.

Findings

Enhanced readout of superconducting qubits in circuit QED with thermal transducers

Effective elimination of optomechanical transducers in quantum measurements

Method handles finite temperature, broadening practical applicability

Abstract

An ever broader range of physical platforms provides the possibility to study and engineer quantum dynamics under continuous measurements. In many experimental arrangements the system of interest is monitored by means of an ancillary device, whose sole purpose is to transduce the signal from the system to the measurement apparatus. Here, we present a method of adiabatic elimination when the transducer consists of an arbitrary number of bosonic modes with Gaussian dynamics while the measured object can be any quantum system. Crucially, our approach can cope with the highly relevant case of finite temperature of the transducer, which is not easily achieved with other methods. We show that this approach provides a significant improvement in the readout of superconducting qubits in circuit QED already for a few thermal excitations, and admits to adiabatically eliminate optomechanical transducers.