# Josephson photodetectors via temperature-to-phase conversion

## TL;DR

This paper proposes a theoretical design for a superconducting Josephson junction-based detector that converts temperature changes into phase shifts, enabling highly sensitive single-photon detection in the GHz to THz range with potential applications in dark matter research.

## Contribution

It introduces a novel temperature-to-phase conversion mechanism in SNS Josephson junctions for photon detection, with detailed predictions of device performance and feasibility.

## Key findings

- Large signal-to-noise ratio >100 for 10 GHz to 10 THz detection
- Resolving power >100 below 50 mK for THz photons
- Electrical NEP of ~10^{-22} W/√Hz at 50 mK

## Abstract

We theoretically investigate the temperature-to-phase conversion (TPC) process occurring in dc superconducting quantum interferometers based on superconductor--normal metal--superconductor (SNS) mesoscopic Josephson junctions. In particular, we predict the temperature-driven rearrangement of the phase gradients in the interferometer under the fixed constraints of fluxoid quantization and supercurrent conservation. This allows sizeable phase variations across the junctions for suitable structure parameters and temperatures. We show that the TPC can be a basis for sensitive single-photon sensors or bolometers. We propose a radiation detector realizable with conventional materials and state-of-the-art nanofabrication techniques. Integrated with a superconducting quantum interference proximity transistor (SQUIPT) as a readout set-up, an aluminum (Al)-based TPC calorimeter can provide a large signal to noise (S/N) ratio $>100$ in the 10~GHz$\cdots$10~THz frequency range, and a resolving power larger than $10^2$ below 50~mK for THz photons. In the bolometric operation, electrical NEP of $\sim10^{-22}$~W$/\sqrt{\text{Hz}}$ is predicted at 50 mK. This device can be attractive as a cryogenic single-photon sensor operating in the giga- and terahertz regime, with applications in dark matter searches.