Advanced photon counting applications with superconducting detectors

Superconducting nanowire single photon detectors (SNSPDs) have emerged as mature detection technology that offers superior performance relative to competing infrared photon counting technologies. SNSPDs have the potential to revolutionize a range of advanced infrared photon counting applications, from quantum information science to remote sensing. The scale up to large area SNSPD arrays or cameras consisting of hundreds or thousands of pixels is limited by efficient readout schemes. This thesis gives a full overview of current SNSPD technology, describing design, fabrication, testing and applications. Prototype 4-pixel SNSPD arrays (30 x 30 µm2 and 60 x 60 µm2) were fabricated, tested and time-division multiplexed via a power combiner. In addition, a photon-number resolved code-division multiplexed 4-pixel array was simulated. Finally, a 100 m calibration-free distributed fibre temperature testbed, based on Raman backscattered photons detected by a single pixel fibre-coupled SNSPD housed in a Gifford McMahon cryostat was experimentally demonstrated with a spatial resolution of approximately 83 cm. At present, it is the longest range distributed thermometer based on SNSPD sensing

Large Area Superconducting Nanowire Single Photon Detector Arrays

Superconducting Nanowire Single Photon Detectors (SNSPDs) are a promising emerging technology for high efficiency single infrared photon detection. Excellent signal-to-noise ratio, high efficiency and good timing resolution can currently be achieved in small single pixel SNSPDs (area smaller than 14×14 μm2). This small area is a severe practical limitation for emerging infrared photon counting applications requiring multimode fibre or free space optical coupling. In this paper we demonstrate fabrication and full optical testing of an array of 2×2 SNSPDs, using nanowires in parallel configuration, covering an active area of 30 × 30 μm2. We report a system detection efficiency (~ 2.6 % @ λ=1550 nm) and low timing jitter (FWHM ~ 70 ps). Moreover, advanced nano-optical characterization, using an innovative cryogenic miniature confocal microscope, enabled us to confirm the high uniformity of patterned nanowires across the entire sensitive area of the SNSPD array

Direct Downhole Temperature Measurement and Real Time Pressure -Enthalpy Model Through Photon Counting Fibre Optic Temperature Sensing

Temperature, pressure and enthalpy data is very important and valuable, both during geothermal drilling and in well operation. We research the possibility of direct downhole measurement of temperature, free calibration, which will result in a real time pressure and enthalpy reporting model. We report on the development of a downhole geothermal brine pressure and enthalpy model, applied to the state-space T-p-X delineations and density (ρ) correlations in flowing gas, liquid and two-phase systems, using the H2O–NaCl geothermal brine thermodynamic formulation. The model was implemented in C programming, running in the NI Lab Windows/CVI user interface. The model is highly dependent on our fibre optic temperature sensor system for a direct temperature measurement. We are working to extend the range of an existing calibration-free fibre optic temperature sensing technique based on photon counting measurements by Raman backscatter (previously developed in collaboration with the US National Institute of Standards and Technology). We aim to extend the range of the system to kilometre length, by increasing the optical power per pulse and reducing the repetition rate of the excitation laser. We will employ superconducting single photon detectors with improved efficiency (5%) housed in a practical, closed-cycle cooling system