Francesco Marsili

Nanowire superconducting single-photon detectors on GaAs for integrated quantum photonic applications

We demonstrate efficient nanowire superconducting single photon detectors (SSPDs) based on NbN thin films grown on GaAs. NbN films ranging from 3 to 5 nm in thickness have been deposited by dc magnetron sputtering on GaAs substrates at 350u2009°C. These films show superconducting properties comparable to similar films grown on sapphire and MgO. In order to demonstrate the potential for monolithic integration, SSPDs were fabricated and measured on GaAs/AlAs Bragg mirrors, showing a clear cavity enhancement, with a peak quantum efficiency of 18.3% at λ=1300u2002nm and T=4.2u2002K.

Single-photon experiments at telecommunication wavelengths using nanowire superconducting detectors

The authors report fiber-coupled superconducting single-photon detectors with specifications that exceed those of avalanche photodiodes, operating at telecommunication wavelength, in sensitivity, temporal resolution, and repetition frequency. The improved performance is demonstrated by measuring the intensity correlation function g(2)(τ) of single-photon states at 1300nm produced by single semiconductor quantum dots.

High efficiency NbN nanowire superconducting single photon detectors fabricated on MgO substrates from a low temperature process

We demonstrate high-performance nanowire superconducting single photon detectors (SSPDs) on bN thin films grown at a temperature compatible with monolithic integration. NbN films ranging from 150 nm to 3 nm in thickness were deposited by dc magnetron sputtering on MgO substrates at 400 degrees C SSPDs were fabricated on high quality NbN films of different thickness (7 to 3 nm) deposited under optimal conditions. Electrical and optical characterizations were performed on the SSPDs. The highest QE value measured at 4.2K is 20% at 1300 nm.High sensitivity ultrafast nanowire superconducting single photon detectors (SSPD) in the near infrared wavelength range have been fabricated with ultrathin (3.5nm) NbN films grown on R-plane sapphire substrates by dc reactive magnetron sputtering in Ar+N2 mixture. These results show for the first time that high performance NbN SSPDs can be realized on different substrates and at lower deposition temperature than previously reported, and opens the way to integration with advanced solid state optical structures. SSPDs have been fabricated by a two mask process using electron beam lithography and reactive ion etching on 3.5nm thick NbN films deposited under optimal conditions on MgO.

Physics and application of photon number resolving detectors based on superconducting parallel nanowires

The parallel nanowire detector (PND) is a photon number resolving (PNR) detector that uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (?100?nm wide, a few nm thick), folded in a meander pattern. PNDs were fabricated on 3?4?nm thick NbN films grown on MgO?(TS = 400??C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. PNDs showed a counting rate of 80?MHz and a pulse duration as low as 660?ps full-width at half-maximum (FWHM). Building the histograms of the photoresponse peak, no multiplication noise buildup is observable. Electrical and optical equivalent models of the device were developed in order to study its working principle, define design guidelines and develop an algorithm to estimate the photon number statistics of an unknown light. In particular, the modeling provides novel insight into the physical limit to the detection efficiency and to the reset time of these detectors. The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed and multiplication noise.

Electrical characterization of superconducting single-photon detectors

Superconducting meanders of NbN thin films have applications as single-photon detectors with high sensitivity in the infrared region. We report here a detailed analysis of the electrical characteristics of such meanders, by studying structures where each wire of the meander is separately contacted. The effect of heating on the superconducting-normal transition of adjacent stripes is evidenced. Moreover, the analysis of the switching current distribution of each wire highlights the high-critical current uniformity achieved by our meander process.

Superconducting parallel nanowire detector with photon number resolving functionality

We present a new photon number resolving detector (PNR), the Parallel Nanowire Detector (PND), which uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (≈100 nm wide, few nm thick), folded in a meander pattern. Electrical and optical equivalents of the device were developed in order to gain insight on its working principle. PNDs were fabricated on 3–4 nm thick NbN films grown on sapphire (substrate temperature T S = 900°C) or MgO (T S = 400°C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. The photoresponse shows a full width at half maximum (FWHM) as low as 660 ps. PNDs showed counting performance at 80 MHz repetition rate. Building the histograms of the photoresponse peak, no multiplication noise buildup is observable and a one-photon quantum efficiency can be estimated to be η ∼ 3% (at 700 nm wavelength and 4.2 K temperature). The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed, and multiplication noise. †Present address: COBRA Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.

High quality superconducting NbN thin films on GaAs

A very promising way to increase the detection efficiency of nanowire superconducting single-photon detectors (SSPDs) consists in integrating them with advanced optical structures such as distributed Bragg reflectors (DBRs) and optical waveguides. This requires transferring the challenging SSPD technology from the usual substrates, i.e. sapphire and MgO, to an optical substrate like GaAs, on which DBRs and waveguides can be easily obtained. Therefore, we optimized the deposition process of few-nm thick superconducting NbN films on GaAs and AlAs/GaAs-based DBRs at low temperatures (substrate temperature T-S = 400 degrees C), in order to prevent As evaporation. NbN films ranging from 150 to 3 nm in thickness were then deposited on single-crystal MgO, GaAs, MgO-buffered GaAs and DBRs by current-controlled DC magnetron sputtering (planar, circular, balanced configuration) of Nb in an Ar + N-2 plasma. 5.5 nm thick NbN films on GaAs exhibit T-C = 10.7 K, Delta T-C = 1.1 K and RRR = 0.7. The growth of such high quality thin NbN films on GaAs and DBRs has never been reported before.

Photon-number-resolving superconducting nanowire detectors

In recent years, photon-number-resolving (PNR) detectors have attracted great interest, mainly because they can play a key role in diverse application fields. A PNR detector with a large dynamic range would represent an ideal photon detector, bringing the linear response of conventional analogue detectors down to the single-photon level. Several technologies, such as InGaAs single photon avalanche detectors (SPADs), arrays of silicon photomultipliers, InGaAs SPADs with self-differencing circuits and transition edge sensors have shown photon number resolving capability. Superconducting nanowires provide free-running single-photon sensitivity from visible to mid-infrared frequencies, low dark counts, excellent timing resolution (<60 ps) and short dead time (~10 ns), at an easily accessible temperature (2–3 K), but they do not inherently resolve the photon number. In this framework, PNR detectors based on arrays of superconducting nanowires have been proposed. In this article we describe a number of methods and device configurations that have been pursued to obtain PNR capability using superconducting nanowire detectors.

Superconducting nanowire photon number resolving detector at telecom wavelength

We demonstrate a photon-number-resolving (PNR) detector, based on parallel superconducting nanowires, capable of resolving up to 5 photons in the telecommunication wavelength range, with sensitivity and speed far exceeding existing approaches.

Erratum: Single photon experiments at telecom wavelengths using nanowire superconducting detectors [Appl. Phys. Lett. 91, 031106 (2007)]

Keywords: avalanche photodiodes ; superconducting photodetectors Reference EPFL-ARTICLE-172849doi:10.1063/1.3323107View record in Web of Science Record created on 2011-12-16, modified on 2016-08-09