Tino Röhlicke

Time-Correlated Single Photon Counting (TCSPC) and continuous time tagging of photon arrival times are very powerful tools in many areas of applied physics [1]. In optical quantum science, they are widely used for the characterization of non-classical light emitters and the detection of coincident photon arrival events. In light of the recent quantum technology initiatives, these timing devices play a central role as crucial technological building blocks. Here, we present a new scalable concept of multi-channel event timers with up to 64 channels, 5 ps digital resolution and accurate long-distance synchronization capabilities using the White Rabbit fiber network protocol [2]. We demonstrate a relative timing precision of about 40 ps to 50 ps r.m.s. over several kilometers distance in network topologies of different complexity and with different fiber lengths, with and without additional network traffic. One set of results measuring across 5 different devices in a simple star-topology using one White Rabbit switch is shown in Fig. 1 as an example. The new event timers have an extremely short dead time of <650 ps, which keeps up with the quick progress of development in the area of superconducting nanowires and other single photon detectors with short recovery times. The event timers feature two data interfaces to the host: a USB interface and a low-latency interface to external FPGAs, on which custom algorithms for real-time data processing can be implemented. In particular, the FPGA interface is presently being employed in a demonstrator of a high speed QKD system as part of the QuPAD project, funded by the German Federal Ministry of Eduaction and research, contract number 13N14953. The new design also provides several valuable features such as adjustable timing offsets for each input channel at full resolution, four external marker inputs for imaging and other synchronization tasks, as well as in/outputs for hardware driven experiment control, as established in various trendsetting instruments developed earlier [3-4]. References [1] P. Kapusta, M. Wahl, and R. Erdmann (eds.), Advanced Photon Counting - Applications, Methods, Instrumentation, (Springer International Publishing, 2015) [2] J. Serrano, P. Alvarez, M. Cattin, E. G. Cota, P. M. J. H. Lewis, T. Włostowski et al., "The White Rabbit Project", Proc. ICALEPCS TUC004, Kobe, Japan (2009). [3] M. Wahl, T. Roehlicke, S. Kulisch, S. Rohilla, B. Kraemer and A.C. Hocke, "Photon arrival time tagging with many channels, sub-nanosecond deadtime, very high throughput, and fiber optic remote synchronization", Rev. Sci. Instrum. 91, 013108 (2020). [4] M. Wahl, H.-J. Rahn, T. Roehlicke, R. Erdmann, G. Kell, A. Ahlrichs, M. Kernbach, A.W. Schell, and O. Benson, "Integrated multichannel photon timing instrument with very short dead time and high throughput ", Rev. Sci. Instrum. 84, 043102 (2013).

Emerging quantum technologies, such as quantum key distribution, increase the demand for reliable tools that enable single-photon generation, manipulation and sensing on an increasingly large scale. In the framework of integrated photonics, these needs can be fulfilled by patterning highly stable photonic devices on monolithic silicon chips in CMOS compatible processes. In this work we show how advanced single-photon detection capabilities are achieved on a silicon chip, realizing a 4x4 array of waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). Our detectors are fabricated from highly uniform superconducting NbTiN thin films in a U-shape geometry atop of silicon nitride strip waveguides [1]. The nanophotonic circuitry is interfaced with scalable 3D polymeric out-of-plane fiber-to-chip couplers [2] featuring high broadband transmission in the telecom regime. In order to address each detector individually via a separate fiber-optic channel, we precisely align a 16-channel 2D fiber array to the 4x4 coupler matrix. We evaluate the performance of our waveguide-integrated SNSPD array in a cost-efficient closed-cycle cryostat at 3.5 K. We find dark count rates below 10 Hz combined with a superior system detection efficiency of up to 50 % at 30 MHz count rate for telecom-wavelength photons. In addition, we achieve 120 ps timing jitter with a simple two-stage room-temperature amplification approach. Our detector arrays pave the way for parallelized multi-channel single-photon detection and will therewith enable ultra-fast quantum key distribution. Furthermore, our approach allows for integrating sophisticated nanophotonic devices with waveguide-coupled single-photon detectors providing additional variability and functionality.