Quantum Noise, Effective Temperature, and Damping in a Superconducting Single-Electron Transistor

TL;DR

This study measures the quantum noise of a superconducting single-electron transistor (S-SET) in a microwave resonator, revealing how its damping and effective temperature depend on bias conditions, with implications for quantum device control.

Contribution

It provides the first direct measurement of quantum noise in an S-SET and introduces an effective bath model to describe its damping and temperature behavior.

Findings

S-SET damping is proportional to differential conductance.

Effective temperature varies with bias, below ambient near certain resonances.

Negative differential conductivity observed when blue detuned.

Abstract

We have directly measured the quantum noise of a superconducting single-electron transistor (S-SET) embedded in a microwave resonator consisting of a superconducting LC tank circuit. Using an effective bath description, we find that the S-SET provides damping of the resonator modes proportional to its differential conductance and has an effective temperature that depends strongly on the S-SET bias conditions. In the vicinity of a double Cooper pair resonance, when both resonances are red detuned the S-SET effective temperature can be well below both the ambient temperature and the energy scale of the bias voltage. When blue detuned, the S-SET shows negative differential conductivity,