Voltage Fluctuations in ac Biased Superconducting Transition-Edge Sensors

TL;DR

This paper analyzes the fundamental noise sources in ac voltage biased superconducting transition-edge sensors, revealing that excess noise arises from Johnson noise of quasiparticles and nonlinear Josephson effects.

Contribution

It provides a detailed explanation of the excess noise in TESs as equilibrium Johnson noise and Josephson frequency harmonics, advancing understanding of noise mechanisms in these sensors.

Findings

Excess noise is explained by Johnson noise of quasiparticles.

Fluctuations at Josephson frequency significantly affect voltage noise.

Noise depends on bath temperature, resistance, and geometry of TES.

Abstract

We present a detailed analysis of the fundamental noise sources in superconducting transition-edge sensors (TESs), ac voltage biased at MHz frequencies and treated as superconducting weak links. We have studied the noise in the resistive transition as a function of bath temperature of several detectors with different normal resistances and geometries. We show that the excess noise, typically observed in the TES electrical bandwidth, can be explained by the equilibrium Johnson noise of the quasiparticles generated within the weak link. The fluctuations at the Josephson frequency and higher harmonics contribute significantly to the measured voltage noise at the detector bandwidth through the nonlinear response of the weak link with a sinusoidal current-phase relation.