Djm David Bitauld

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 350 °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=1300 nm and T=4.2 K.

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.

Enhanced spontaneous emission in a photonic-crystal light-emitting diode

We report direct evidence of enhanced spontaneous emission in a photonic-crystal (PhC) light-emitting diode. The device consists of p-i-n heterojunction embedded in a suspended membrane, comprising a layer of self-assembled quantum dots. Current is injected laterally from the periphery to the center of the PhC. A well-isolated emission peak at 1.3μm from the PhC cavity mode is observed, and the enhancement of the spontaneous emission rate is clearly evidenced by time-resolved electroluminescence measurements, showing that our diode switches off in a time shorter than the bulk radiative and nonradiative lifetimes.

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.

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.

Waveguide single-photon detectors for integrated quantum photonics

We report the first waveguide single-photon detectors. They are based on superconducting nanowires patterned on top of GaAs/AlGaAs waveguides and are suitable for monolithic integration with single-photon sources and passive quantum optical networks.

NbN nanowire superconducting single photon detectors fabricated on MgO substrates

We report on the fabrication and characterization of high performance nanowire superconducting single photon detectors (SSPD) on MgO substrates. The deposition of the superconducting material (NbN) has been performed by magnetron sputtering at 400°C. This deposition temperature is low enough to be compatible with the fabrication on traditional optical materials like GaAs. First, SSPD meanders covering a surface of 5 × 5 µm2 were characterized. We measured quantum efficiencies up to 20% at 1300 nm. Then, we used a straight 250 µm-long NbN nanowire to perform a spatially resolved measurement of the efficiency. Both efficiency dips and peaks were observed. The dips were correlated to lithographic defects, as confirmed by scanning electron microscopy. Conversely, no evidence of a lithographic origin of efficiency peaks was found.

Nanowire superconducting single-photon detectors integrated with optical microcavities based on GaAs substrates

Nanowire superconducting single photon detectors (SSPDs) are superior detectors of choice for many applications particularly in quantum information and communication technology. SSPDs excellent sensitivity and time resolution are brought about by the ultrafast transition of the very thin and narrow NbN nanowire meander from superconducting to normal state upon absorption of a single photon at near-infrared wavelengths [1]. However, low optical absorption in the ultrathin nanowire structures, puts a limit on the detection efficiency of these devices. A promising approach to improve the photon absorption in SSPDs is integrating them with advanced optical structures [2]. In this work, we report on the successful integration of SSPDs with optical cavity based on GaAs/AlAs distributed Bragg reflector (DBR) to enhance their detection efficiency.

Electrical injection of a photonic crystal nanocavity

The possibility of electrical pumping of a single QD and the integration of such a device in an opto-electronic circuit would be a fundamental step towards achieving an ldquoon demandrdquo single photon source. In this paper we describe the fabrication process and preliminary results of a Light Emitting Diode (LED) integrated with a photonic crystal (PhC) nanocavity on a GaAs membrane. We demonstrate effective electric pumping of the QDs embedded into the membrane by contacting the doped layers (p and n) of the thin membrane, and the excitation of cavity modes of the PhC nanocavity fabricated on it at telecom wavelength.

Enhancement of the recombination rate of InAs quantum dots in a photonic crystal light emitting diode

InAs quantum dots emitting at 1.3 mum and located inside a photonic crystal membrane nanocavity are studied by electrical pumping. An increase of the recombination rate is observed for quantum dots in resonance with the cavity mode.