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E-book Technology and readout for scaling up superconducting nanowire single-photon detectors
Detecting single photons, the quanta of the electromagnetic eld, is of great signicance inscience and engineering. Aside from allowing to detect electromagnetic radiation with thehighest, quantum-limited sensitivity, it also enables numerous experiments in fundamentalphysics. Because of its universal quality, there is a wide range of applications for single-photondetectors in elds like optical communication, astronomy, spectroscopy, ranging, radiometry,and medical imaging [1].The rst device able to detect single-photons was the photomultiplier tube (PMT) which takesadvantage of the photoelectric effect and electron multiplication. Nowadays, semiconductor-based single-photon avalanche diodes (SPAD) for the visible and near-infrared spectrum areestablished as well. They are easy to operate and require, if any, only modest cooling. However,SPADs suffer from high dark-count rates in a trade-off with the detection eciency [2,3] and, most importantly, a limited bandwidth due to the semiconductors’ comparativelylarge bandgap on the order of1 eVat room temperature. Single-photon detectors based onsuperconductors do not have this limitation because of the much smaller energy gap of onlyfew meV (although not directly comparable because of different detection mechanisms). Fortheir operation, however, they have to be cooled below or close to the critical temperature,typically in the range of few Kelvin.One of the most promising detectors in this category, the superconducting nanowire single-photon detector (SNSPD), is based on a current-carrying superconducting nanostripe [4, 5].When biased close to its switching current, the absorption of a single photon is sucientto drive a part of the nanostripe into the normal state, which can be registered as a voltagepulse across the detector. The SNSPD response offers no inherent energy resolution but is,at the same time, largely insensitive to readout noise. Due to continued efforts in detectordevelopment, SNSPDs have been demonstrated with count rates above2 GHz[6], systemdetection eciencies of?98 %[7], a timing jitter below3 ps[8], and dark-count rates belowone per hour [9]. Another key feature of SNSPDs is their suitability for wavelengths farbeyond the visible range [10, 11]. In particular, detecting photons in the mid-infrared range(3to10)?mis of interest for novel applications, e.g., in astronomy [12] or molecular science [13,14], but is not covered by other types of single-photon detectors.
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