Single-photon detectors and nanoscale superconducting devices are two major candidates for realizing quantum technologies. Superconducting-nanowire single-photon detectors (SNSPDs) comprise these two solid-state and optic aspects enabling high-rate (1.3 Gb s −1 ) quantum key distribution over long distances (>400 km), long-range quantum communication (>1200 km), as well as space communication (239 000 miles). The attractiveness of SNSPDs stems from competitive performance in the four single-photon relevant characteristics at wavelengths ranges from UV to the mid-IR: high detection efficiency, low false-signal rate, low uncertainty in photon time arrival, and fast reset time. However, to date, these characteristics cannot be optimized simultaneously. In this review, the mechanisms that govern these four characteristics are presented, and it is demonstrated how they are affected by material properties and device design as well as by the operating conditions, allowing aware optimization of SNSPDs. Based on the evolution in the existing literature and state of the art, it is proposed how to choose or design the material and device for optimizing SNSPD performance, while possible future opportunities in the SNSPD technology are also highlighted.

Superconducting quantum interference devices (SQUIDs) are used for applications ranging from sensitive magnetometers to low-temperature electronics and quantum computation. We introduce a planar nano SQUID that was made with a single lithographic step out of NbN films as thin as 3 nm on a Si chip. The fabrication process of weak links that are 45 nm in width, and 165 nm in length, which were designed to account for overcoming current crowding are presented. Operation at a temperature range of 20 mK to 5 K as well as at 1 T parallel, and 10 mT perpendicular magnetic fields is demonstrated, while potential operation higher than 8 T has also been shown. The broad range of applicability of a single device as well as its scalability are promising for on-chip integrability that may open new technological possibilities, including in quantum and electro-optical circuiting. Text:Superconductors are materials that exhibit quantum behavior at the macroscopic scale and hence are attractive in the current race for quantum technologies. Likewise, the lack of resistance in these materials facilitates them for low-power devices, while it also allows them to demonstrate high sensitivity to lowpower electromagnetic radiation, which in turn is advantageous for detection technologies. Prominent examples include logic devices, 1,2 gamma and x-ray photon sensors 3-6 and IR single-photon detectors. 7-9

Controlling both the amplitude and phase of the quantum order parameter in nanostructures is important for next-generation information and communication technologies.The long-range coherence of attractive electrons in superconductors render these materials as a nearly ideal platform for such applications. To-date, control over has remained limited to the macroscopic scale, either by adjusting untunable materials properties, such as film thickness, stoichiometry and homogeneity or by tuning external magnetic fields. Yet, although local tuning of is desired, the lack of electric resistance in superconductors, which may be advantageous for some technologies hinders convenient voltage-bias tuning. Likewise, challenges related to nanoscale fabrication of superconductors encumber local tunability of .Here, we demonstrate local tunability of , obtained by patterning with a single lithography step a Nb nano superconducting quantum interference device (nano-SQUID) that is biased at its nano bridges. Our design helped us reveal also unusual electric characteristics-effective zero inductance, which is promising for quantum technologies and nanoscale magnetic sensing.Finally, we accompanied our experimental results by a semi-classical model, which not only is extending the applicability of our devices, but is also useful for describing planar nano-SQUIDs in general.

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