Quantum detector tomography of a 2x2 multi-pixel array of superconducting nanowire single photon detectors

TL;DR

This paper demonstrates quantum detector tomography on a 2x2 superconducting nanowire single photon detector array, enabling direct extraction of key performance metrics without detailed physical models.

Contribution

It introduces a method to determine detector figures of merit directly from POVM elements, providing a practical approach for characterizing multi-pixel photon detectors.

Findings

Detector efficiency and dark-count probabilities agree with independent measurements.

Cross-talk probability can be intuitively defined operationally.

Proper parameter selection is crucial to avoid data oversmoothing.

Abstract

We demonstrate quantum detector tomography of a commercial 2x2 array of superconducting nanowire single photon detectors. We show that detector-specific figures of merit including efficiency, dark-count and cross-talk probabilities can be directly extracted, without recourse to the underlying detector physics. These figures of merit are directly identified from just four elements of the reconstructed positive operator valued measure (POVM) of the device. We show that the values for efficiency and dark-count probability extracted by detector tomography show excellent agreement with independent measurements of these quantities, and we provide an intuitive operational definition for cross-talk probability. Finally, we show that parameters required for the reconstruction must be carefully chosen to avoid oversmoothing the data.