Inelastic Backaction due to Quantum Point Contact Charge Fluctuations

TL;DR

This paper theoretically analyzes how nonequilibrium charge fluctuations in a quantum point contact induce inelastic backaction on a nearby double quantum-dot qubit, deriving bounds and expressions for transition rates and distinguishing noise mechanisms.

Contribution

It introduces a theoretical framework linking QPC charge fluctuations to qubit transitions, deriving bounds from the Heisenberg uncertainty principle, and distinguishes noise mechanisms through numerical analysis.

Findings

Charge noise and shot noise backaction mechanisms can be distinguished.

Derived lower bounds on qubit transition rates based on measurement backaction.

Enhanced charge noise sensitivity explained by interference effects similar to Friedel oscillations.

Abstract

We study theoretically transitions of a double quantum-dot qubit caused by nonequilibrium charge fluctuations in a nearby quantum point contact (QPC) used as a detector. We show that these transitions are related to the fundamental Heisenberg backaction associated with the measurement, and use the uncertainty principle to derive a lower bound on the transition rates. We also derive simple expressions for the transition rates for the usual model of a QPC as a mesoscopic conductor, with screening treated at the RPA level. Finally, numerical results are presented which demonstrate that the charge noise and shot noise backaction mechanisms can be distinguished in QPCs having nonadiabatic potentials. The enhanced sensitivity of the charge noise to the QPC potential is explained in terms of interference contributions similar to those which cause Friedel oscillations.