Emission and Absorption quantum noise measurement with an on-chip resonant circuit

TL;DR

This paper demonstrates on-chip quantum noise measurements in a superconducting resonant circuit, distinguishing emission and absorption noise, and directly measuring quasiparticle tunneling noise with frequency dependence.

Contribution

It introduces a method using a superconductor-insulator-superconductor junction to separately measure emission and absorption noise in a superconducting circuit.

Findings

Absorption noise relates to zero point fluctuations at low temperature.

Emission noise appears at higher temperatures.

Quasiparticle tunneling noise shows strong frequency dependence.

Abstract

Using a quantum detector, a superconductor-insulator-superconductor junction, we probe separately the emission and absorption noise in the quantum regime of a superconducting resonant circuit at equilibrium. At low temperature the resonant circuit exhibits only absorption noise related to zero point fluctuations whereas at higher temperature emission noise is also present. By coupling a Josephson junction, biased above the superconducting gap, to the same resonant circuit, we directly measure the noise power of quasiparticles tunneling through the junction at two resonance frequencies. It exhibits a strong frequency dependence, consistent with theoretical predictions.