Superconducting nanowire single-photon detectors for advanced photon-counting applications
Natarajan, Chandra Mouli
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The ability to detect infrared photons is increasingly important in many elds of scienti c endeavour, including astronomy, the life sciences and quantum information science. Improvements in detector performance are urgently required. The Superconducting Nanowire Single-Photon Detector (SNSPD/SSPD) is an emerging single-photon detector technology o ering broadband sensitivity, negligible dark counts and picosecond timing resolution. SNSPDs have the potential to outperform conventional semiconductor-based photon-counting technologies, provided the di culties of low temperature operation can be overcome. This thesis describes how these important challenges have been addressed, enabling the SNSPDs to be used in new applications. A multichannel SNSPD system based on a closed-cycle refrigerator has been constructed and tested. E cient optical coupling has been achieved via carefully aligned optical bre. Fibre-coupled SNSPDs based on (i) NbN on MgO substrates and (ii) NbTiN on oxidised Si substrates have been studied. The latter give enhanced performance at telecom wavelengths, exploiting the re ection from the Si=SiO2 interface. Currently, the detector system houses four NbTiN SNSPDs with average detection e ciency >20% at 1310 nm wavelength. We have employed SNSPDs in the characterisation of quantum waveguide circuits, opening the pathway to operating this promising platform for optical quantum computing for the first time at telecom wavelengths.