Quantum-limited charge detection with two quantum point contacts

TL;DR

This paper proposes a scheme using two quantum point contacts in series to achieve quantum-limited charge detection, surpassing single contact limitations and enhancing sensitivity through multiple reflections.

Contribution

It introduces a novel configuration of two quantum point contacts for quantum-limited detection, which was not feasible with a single contact, and analyzes conditions for optimal performance.

Findings

Quantum-limited detection is achievable with two quantum point contacts in series.

Multiple reflections enhance detection sensitivity.

Single quantum point contact cannot achieve quantum-limited detection under the same conditions.

Abstract

We present a scheme for tuning two quantum point contacts as a quantum-limited charge detector. Based on the scattering matrix approach, we analyze a general condition of quantum-limited detection with a single-channel quantum detector possessing time-reversal symmetry. From this analysis we find that quantum-limited detection can be easily realized with two quantum point contacts connected in series, which is not possible if only a single quantum point contact is used. We also discuss the sensitivity enhancement due to multiple reflections of the two point contacts.