A Path to Superconducting Nanowire Readout of Xe- based detectors

With near-unity quantum efficiencies (QE), ultra-low dark count rates down to 10-4 Hz/device and exquisite sub-10-ps-timing resolution, Superconducting Nanowire Single Photon Detectors (SNSPDs) with vacuum-ultraviolet (VUV) sensitivity offer a potential step change as a new readout technology for a broad range of scintillator detectors used by the PPAN community (LXe, LHe,

LAr) and have application in many non-PPAN areas, such as UV imaging techniques in the life sciences and as a low-noise readout for quantum technology. Most commercially available SNSPD devices target infrared wavelengths, and whilst some UV models are available they are not optimised

for 178 nm VUV Xe light. This project brings together UK expertise in LXe*detectors with world-class capability in SNSPD design and fabrication, to deliver a proof-of-principle demonstration of a VUV-sensitive SNSPD device and to develop a range of novel applications across PPAN, quantum technology and the life sciences that are enabled by this new capability.

Due to its inherent scalability, dark matter detectors based on the UK*pioneered LXe-technology have led the search for intermediate-mass dark matter for more than a decade. Alongside Xe target mass and stringent

radiopurity requirements, the key driver for improved sensitivity for low*energy signals is the efficiency with which the 175 nm VUV scintillation light is detected. At these wavelengths, traditional readout devices such as VUV*sensitive photomultiplier tubes (PMTs) and Si-photomultipliers (SiPM) achieve 25-35% QE and as such readout with a > 90% QE SNSPD would be a

significant improvement. The typical requirement of a triple-coincidence scintillation signal detected across multiple photosensors means this would result in an order of magnitude increase in signal efficiency for low mass dark matter and 8-Boron solar neutrinos.

The key objectives of this project are to demonstrate the viability of a VUV*sensitive SNSPD device and to establish the feasibility and develop cases that leverage this new capability, including their use for readout of compact Xe*based particle detectors, VUV fluorescence spectroscopy, and ion-trap quantum computers. The project will follow a staged approach to characterise existing SNSPD detectors developed by Prof.

Hadfield's group at the University of Glasgow: first, demonstrate the performance of the SNSPD to a VUV signal using double-coincident VIS (400 nm) events as a proxy; then the characterisation of VUV transmittance in solarisation-resistant optical fibres using VUV SiPM devices; which will enable coupling the SNSPD device, first to a monochromatic light source and then to a Xe scintillation cell for complete characterisation.