Qubits as devices to detect the third moment of current fluctuations

TL;DR

This paper proposes using controllable two-level quantum systems (qubits) to detect the third moment of current fluctuations by analyzing their decay behavior, with a derived Master Equation linking the decay oscillations to the third moment.

Contribution

It introduces a theoretical framework and experimental proposal for using qubits as detectors of the third moment of current fluctuations, extending previous methods to higher-order noise detection.

Findings

Derived a Master Equation valid to third order in system-environment coupling.

Showed that qubit decay exhibits oscillations proportional to the third moment.

Discussed an experimental setup to observe these effects.

Abstract

Under appropriate conditions controllable two-level systems can be used to detect the third moment of current fluctuations. We derive a Master Equation for a quantum system coupled to a bath valid to the third order in the coupling between the system and the environment. In this approximation the reduced dynamics of the quantum system depends on the frequency dependent third moment. Specializing to the case of a controllable two-level system (a qubit) and in the limit in which the splitting between the levels is much smaller than the characteristic frequency of the third moment, it is possible to show that the decay of the qubit has additional oscillations whose amplitude is directly proportional to the value of the third moment. We discuss an experimental setup where this effect can be seen.