Technology and Readout for Scaling up Superconducting Nanowire Single-Photon Detectors

Description

Detecting electromagnetic radiation at the quantum limit is essential for a wide range of applications, and superconducting nanowire single-photon detectors (SNSPDs) are among the highest-performing devices for this task. However, scaling SNSPDs from few-pixel devices to large detector arrays while preserving their beneficial metrics remains challenging. In this work, three advances toward the realization of SNSPD arrays are presented. Atomic layer deposition is employed to enable uniform superconducting niobium nitride films of only few-nanometer thickness suitable for large-area devices. To operate and read out multiple detectors with a reduced number of lines, a frequency-multiplexing scheme is investigated, in particular regarding its effect on the resetting behavior and duty cycle of the detector. Finally, efficient optical coupling from free space and optical fibers onto the active area of the detectors is achieved by directly integrating SNSPDs with free-form polymer structures. Kurzfassung Contents Introduction Superconducting nanowire single-photon detectors Superconducting detectors Operation principle of SNSPDs Hotspot formation Detection mechanism Response dynamics Detection metrics Detection efficiency and spectral dependence Dark-count rate Maximum count rate Other metrics Detector materials State-of-the-art NbN thin film deposition SNSPD arrays Multiplexing schemes Frequency-multiplexed SNSPDs Optical coupling Free-space coupling Fiber coupling On-chip coupling Summary Atomic-layer-deposited NbN thin films Atomic layer deposition of NbN Properties of ALD-NbN Film properties Micro- and nanobridge properties Variation of the ICP-to-sample distance Spatial uniformity of ALD-NbN Morphological uniformity Compositional uniformity and crystal structure Spread of superconducting properties Summary ALD-NbN SNSPDs Detector design and fabrication Detector design Detector patterning Experimental setup Optical detector characterization Bias and photon-rate dependence Spectral dependence Thickness-dependent dark and photon counts Summary Frequency-multiplexed SNSPDs Array design and fabrication Self-resetting behavior Simulation of DC- and RF-biased detectors Synchronized gated detection Experimental setup Phase-sensitive detection efficiency Duty cycle Matched-filter array readout Concept Proof-of-principle experiment Future readout of RF-SNSPD arrays Summary Optical coupling Microlens-integrated RF-SNSPD Microlens concept and fabrication Optical measurements of the microlens gain Optical packaging of SNSPDs with photonic wire bonds Detector design and fabrication Direct laser-writing of the bonds Optical measurements of the PWB coupling efficiency Summary Nanowire characterization with M-KING Layout and fabrication Current-dependent microwave properties Determination of the depairing current Noise current Summary Conclusions and outlook List of Figures List of Tables Nomenclature Bibliography List of Own Publications Peer-reviewed Journals Conferences Danksagung