Complete experimental characterization of a superconducting multiphoton nanodetector

TL;DR

This paper introduces a comprehensive method for characterizing superconducting multiphoton nanodetectors, separating nonlinear detection effects from linear losses, crucial for quantum information applications.

Contribution

It provides the first full experimental characterization of a superconducting nanodetector with multiphoton sensitivity, enhancing understanding of its physics and performance.

Findings

Successfully separated nonlinear detection from linear losses.

Demonstrated multiphoton sensitivity regimes.

Provided quantitative physics insights into the detector.

Abstract

We present a complete method to characterize multiphoton detectors with a small overall detection efficiency. We do this by separating the nonlinear action of the multiphoton detection event from linear losses in the detector. Such a characterization is a necessary step for quantum information protocols with single and multiphoton detectors and can provide quantitative information to understand the underlying physics of a given detector. This characterization is applied to a superconducting multiphoton nanodetector, consisting of an NbN nanowire with a bowtie-shaped subwavelength constriction. Depending on the bias current, this detector has regimes with single and multiphoton sensitivity. We present the first full experimental characterization of such a detector.