Physics and application of photon number resolving detectors based on superconducting parallel nanowires

TL;DR

This paper presents the design, fabrication, and characterization of superconducting parallel nanowire detectors capable of resolving photon numbers with high speed and sensitivity, offering improvements over existing detectors.

Contribution

It introduces a novel superconducting nanowire-based PNR detector with detailed modeling, demonstrating superior performance and providing insights into physical detection limits.

Findings

Counting rate of 80 MHz

Pulse duration as low as 660 ps

No observable multiplication noise buildup

Abstract

The Parallel Nanowire Detector (PND) is a photon number resolving (PNR) detector which uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (100 nm-wide, few nm-thick), folded in a meander pattern. PNDs were fabricated on 3-4 nm thick NbN films grown on MgO (TS=400C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. PNDs showed a counting rate of 80 MHz and a pulse duration as low as 660ps full width at half maximum (FWHM). Building the histograms of the photoresponse peak, no multiplication noise buildup is observable. Electrical and optical equivalent models of the device were developed in order to study its working principle, define design guidelines, and develop an algorithm to estimate the photon number statistics of an unknown light. In particular, the modeling provides novel insight of the physical limit to the detection efficiency and to the reset time of these detectors. The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed, and multiplication noise.