Superconducting Nanostrip Photon-Number-Resolving Detector for Photon Distribution Reconstruction

Single photon detectors based on superconducting nanostrips demonstrated high performance at 1550 nm, combining high efficiency and low noise. Arranged in arrays, these devices can implement photon-number resolution, expanding the range of applicability of superconducting detectors. A detector of this kind was used in our recent work to implement the annihilation operator and the characterization of quantum states in terms of their photon number distribution. The reconstructed distributions were consistent with the theoretical predictions, exhibiting fidelities higher than 99.9%. In this work, this procedure was repeated with each pixel singularly to define a detector fidelity matrix, evaluating the fidelity among all the possible pixel combinations. In this way, we introduce an additional tool that quantifies not only the quality of the reconstructed photon number distribution when compared to the theoretical expectation, but also the mutual fidelity when different pixels are chosen as independent, and then the fabrication uniformity.