Superconducting single-photon detector for the visible and infrared spectral range

Abstract

We present results on dark count rates and spectral sensitivities of superconducting single-photon detectors in the visible and near-infrared spectral range. The active detector element is a nanometre-sized (a few nanometres thick and less than 100 nm wide) meander line carrying a supercurrent. The superconducting materials are NbN and Nb, respectively. The NbN detector exhibited a flat spectral sensitivity up to about 2.4 mm. Fluctuations of the superconducting order parameter are considered as a major source of dark count events. A simple model and its limitations to explain the observed dark count rates is discussed. IntroductionSuperconducting devices make some of the most sensitive detectors for a variety of physical quantities, e.g. transition-edge bolometers for radiation [1] or superconducting quantum interference devices for magnetic flux [2]. Essentially, this is due to the special quantum nature of the superconducting state and the low operating temperatures reducing intrinsic noise to a minimum. Single-photon detectors are by definition the most sensitive quantum radiation detectors and once again superconductors open up new possibilities for improvements in detector characteristics compared to their classical counterparts, e.g. photomultiplier tubes [3] or semiconducting quantum detectors [4,5].It is thought that photons absorbed by supercurrent carrying detectors of the type which are presented here cause a normal conducting perturbation that subsequently can be detected as a voltage transient. Various details of the associated theoretical model [6] still have to be verified experimentally. However, the detectors have already been demonstrated to be characterized by ultrafast response times resulting in maximum count rates up to 10 GHz and reasonably high quantum efficiency at very low dark count rates [7]. Conceivable applications could include such diverse areas as future astronomy projects or X-ray spectroscopy. In astronomy there is great need for detectors having background limited sensitivity in the infrared and submillimetre spectral range and X-ray

Spectral cut-off in the efficiency of the resistive state formation caused by absorption of a single-photon in current-carrying superconducting nano-strips

“…The spectral dependence should repeat the temperature dependence of the dark count rate at a fixed bias current. Available experimental data 2,13 qualitatively confirm this conclusion.…”

“…Depending on the cross-section dark counts in one-dimensional superconductors may originate from the spontaneous formation of either classical 10 or quantum 11 phase-slips. When the cross-section confining the current path extends over the coherence length, dark counts can appear due to discrete fluctuations of the superconducting order parameter 12,13 and/or number fluctuations in the gas of bundled magnetic vortices 14 . It has been observed in many experiments that the dark count rate strongly depends on the bias current.…”

On the genesis and evolution of Integrated Quantum Optics

“…Such detectors have shown an efficiency of up to 50% at the telecom wavelengths for a noise comparable to that of the Si-APDs [174][175][176]. However, the implementation of these devices is still challenging, both in terms of manufacturing and reproducibility, and complicated, both in terms of handling and operational expenses (liquid helium cooling).…”

Noise of a Superconducting Photon Detector

“…However, as the device size becomes comparable to the superconducting coherence length in one or more dimensions fluctuation effects play an increasingly important role [1] in the noise performance of the device. A recently proposed single-photon detection mechanism in a nano-wide superconducting strip [2] have been shown to have attractively low noise [3] but the temperature and current variations of the noise level in such a detector [4] are to a large extent inconsistent with an intuitive hot-spot model [2], [5]. In this paper we report on the temperature and current-dependence of dark count rates for a superconducting photon detector and discuss these results with respect to fluctuations of the chemical potential and the current-assisted unbinding of vortex-antivortex pairs related to the Kosterlitz-Thouless transition in thin superconducting films.…”