Inhomogeneous critical current in nanowire superconducting single-photon detectors

A superconducting thin film with uniform properties is the key to realize nanowire superconducting single-photon detectors (SSPDs) with high performance and high yield. To investigate the uniformity of NbN films, we introduce and characterize simple detectors consisting of short nanowires with length ranging from 100nm to 15{\mu}m. Our nanowires, contrary to meander SSPDs, allow probing the homogeneity of NbN at the nanoscale. Experimental results, endorsed by a microscopic model, show the strongly inhomogeneous nature of NbN films on the sub-100nm scale.Comment: 10 pages, 4 figure

Series-nanowire photon number resolving detector counting up to 24 photons

A 24-pixel photon-number-resolving-detector (PNRD) based on superconducting nanowires in a series configuration is demonstrated. Distinct output levels corresponding to the detection of 0-25 photons are observed, due to the high signal-to-noise ratio

Photon counting with a 24-pixel SSPD based photon number resolving detector

In this work we present the fabrication and the electro-optical characterization of a 24-pixel photon-number-resolving-detector, based on superconducting nanowires in a series configuration. In this configuration, the electrical responses of each firing pixel sum up into a single readout pulse whose height is proportional to the detected photon number. This device can resolve up to twenty-five distinct output levels corresponding to the detection of n = 0 - 24 photons. Due to its large dynamic range, high sensitivity, high speed and wide wavelength range, this device has potential for linear detection in the few tens of photons range

Photon-counting and analog operation of a 24-pixel photon number resolving detector based on superconducting nanowires

We investigate the transition from the photon-counting to the linear operation mode in a large-dynamic range photon-number-resolvingdetector (PNRD). A 24-pixel photon-number-resolving-detector, based on superconducting nanowires in a series configuration, has been fabricated and characterized. The voltage pulses, generated by the pixels, are summed up into a single readout pulse whose height is proportional to the detected photon number. The device can resolve up to twenty-five distinct output levels corresponding to the detection of n = 0-24 photons. Due to its large dynamic range, high sensitivity, high speed and wide wavelength range, this device has potential for linear detection in the few tens of photons range.\u3cbr/\u3eWe show its application in the detection of analog optical signals at frequencies up to few hundred MHz and investigate the limits related to the finite number of pixels and to the pixel's dead time

Integration of single-photon sources and detectors on GaAs

\u3cp\u3eQuantum photonic integrated circuits (QPICs) on a GaAs platform allow the generation, manipulation, routing, and detection of non-classical states of light, which could pave the way for quantum information processing based on photons. In this article, the prototype of a multi-functional QPIC is presented together with our recent achievements in terms of nanofabrication and integration of each component of the circuit. Photons are generated by excited InAs quantum dots (QDs) and routed through ridge waveguides towards photonic crystal cavities acting as filters. The filters with a transmission of 20% and free spectral range ≥66 nm are able to select a single excitonic line out of the complex emission spectra of the QDs. The QD luminescence can be measured by on-chip superconducting single photon detectors made of niobium nitride (NbN) nanowires patterned on top of a suspended nanobeam, reaching a device quantum efficiency up to 28%. Moreover, two electrically independent detectors are integrated on top of the same nanobeam, resulting in a very compact autocorrelator for on-chip g\u3csup\u3e(2)\u3c/sup\u3e(τ) measurements.\u3c/p\u3

Probing the hotspot interaction length in NbN nanowire superconducting single photon detectors

\u3cbr/\u3e\u3cbr/\u3eWe measure the maximal distance at which two absorbed photons can jointly trigger a detection event in NbN nanowire superconducting single photon detector microbridges by comparing the one-photon and two-photon efficiencies of bridges of different overall lengths, from 0 to 400 nm. We find a length of 23 ± 2 nm. This value is in good agreement with the size of the quasiparticle cloud at the time of the detection event.\u3cbr/\u3e\u3cbr/\u3e\u3cbr/\u3eNanowire superconducting single photon detectors (SSPDs)1 are a crucial technology for a variety of applications.2 These devices consist of a thin superconducting film which detects photons when biased to a significant fraction of its critical current. Although details of the microscopic mechanism are still in dispute,3 the present understanding of this process in Niobium Nitride (NbN) SSPDs is as follows:4–13 after the absorption of a photon, a cloud of quasiparticles is created, which is known as a hotspot. This cloud diffuses, spreading out over some area of the wire. This causes the redistribution of bias current, which unbinds a vortex from the edge of the wire, if the applied bias current is such that the current for vortex entry is exceeded. The transition of a vortex across the wire creates a normal-state region, which grows under the influence of Joule heating from the bias current, leading to a voltage pulse and a detection event.1

Quantum tomography of superconducting single photon detectors

Nanowire superconducting single photon detectors (SSPDs) consist of a thin (~ 4 to 6 nm) and narrow (~ 50 to 200 nm) superconducting wire biased close to the critical current. Operating conditions are such that the absorption of one or more photons locally transfers the detector to its normal state, which then results in a detectable electrical pulse. SSPDs are versatile detectors that operate in a wide wavelength range (from UV to mid-infrared) with almost negligible dark counts. They are typically shaped in the form of a meander to cover a sizeable fraction of a sufficiently large 2D surface, but other shapes have also been produced and are often easier to analyse. Until recently, the working principle of SSPDs was badly understood and several competing theory were formulated