Back-action noise in strongly interacting systems: the dc SQUID and the interacting quantum point-contact

TL;DR

This paper analyzes the back-action noise and measurement efficiency of a dc SQUID and a quantum point contact in a Luttinger liquid, demonstrating they can reach the quantum limit due to their integrability.

Contribution

It introduces a mapping to a dissipative tight-binding model to explain how these systems achieve the quantum limit despite multiple transport processes.

Findings

Systems can reach the quantum limit even with multiple transport channels

Mapping to a dissipative tight-binding model explains measurement efficiency

Integrability of the systems is key to their quantum-limited performance

Abstract

We study the back-action noise and measurement efficiency (i.e. noise temperature) of a dc SQUID amplifier, and equivalently, a quantum point contact detector formed in a Luttinger liquid. Using a mapping to a dissipative tight-binding model, we show that these systems are able to reach the quantum limit even in regimes where several independent transport processes contribute to the current. We suggest how this is related to the underlying integrability of these systems.