Optical photon detection in Al Superconducting Tunnel Junctions

TL;DR

This paper demonstrates the fabrication and testing of aluminium superconducting tunnel junctions capable of high-sensitivity optical photon detection with low leakage and high responsivity, suitable for quantum sensing applications.

Contribution

It introduces a fabrication process for low-leakage, homogeneous aluminium superconducting tunnel junctions with high responsivity and charge amplification for optical photon detection.

Findings

Low leakage currents (~100 fA/um2) achieved

Charge amplification factors >100 demonstrated

Total resolving power of 13 for 500 nm photons

Abstract

We report on the successful fabrication of low leakage aluminium superconducting tunnel junctions with very homogeneous and transparent insulating barriers. The junctions were tested in an adiabatic demagnetisation refrigerator with a base temperature of 35 mK. The normal resistance of the junctions is equal to ~7 uohm cm2 with leakage currents in the bias voltage domain as low as 100 fA/um2. Optical single photon counting experiments show a very high responsivity with charge amplification factors in excess of 100. The total resolving power (including electronic noise) for 500 nm photons is equal to 13 compared to a theoretical tunnel limited value of 34. The current devices are found to be limited spectroscopically by spatial inhomogeneities in the detectors response