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Optics Express

Cryo-compatible opto-mechanical low-voltage phase-modulator integrated with superconducting single-photon detectors

Fabian Beutel, Thomas Grottke, Martin A. Wolff, Carsten Schuck, Wolfram H. P. Pernice

Published Jun 23, 2022• 15 citations
Publisher

Abstract

Photonic integrated circuits (PICs) have enabled novel functionality in quantum optics, quantum information processing and quantum communication. PICs based on Silicon Nitride (Si3N4) provide low-loss passive components and are compatible with efficient superconducting nanowire single-photon detectors (SNSPDs). For realizing functional quantum photonic systems, the integration with active phase-shifters is needed which is challenging at the cryogenic temperatures needed for operating SNSPDs. Here we demonstrate a cryo-compatible phase shifter using a low-voltage opto-mechanical modulator and show joint operation with SNSPDs at 1.3 K. We achieve a half-wave voltage of 4.6 V, single-photon detection with 88% on-chip detection efficiency (OCDE) and a low timing jitter of 12.2 ps. Our approach allows for operating reconfigurable quantum photonic circuits with low dissipation in a cryogenic setting.

DOI
10.1364/oe.462163

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Photonic integrated circuits (PICs) have enabled novel functionality in quantum optics, quantum information processing and quantum communication. PICs based on Silicon Nitride (Si3N4) provide low-loss passive components and are compatible with efficient superconducting nanowire single-photon detectors (SNSPDs). For realizing functional quantum photonic systems, the integration with active phase-shifters is needed which is challenging at the cryogenic temperatures needed for operating SNSPDs. Here we demonstrate a cryo-compatible phase shifter using a low-voltage opto-mechanical modulator and show joint operation with SNSPDs at 1.3 K. We achieve a half-wave voltage of 4.6 V, single-photon detection with 88% on-chip detection efficiency (OCDE) and a low timing jitter of 12.2 ps. Our approach allows for operating reconfigurable quantum photonic circuits with low dissipation in a cryogenic setting.
Superconducting Nanowire Single Photon Detectors (SNSPD) have set leading performance benchmarks in terms of detection efficiency, low noise operation, speed, and timing accuracy. Besides scaling up the numbers of individually addressable nanowire detector channels, integration with nanophotonic functionalities as well as optical and electrical multiplexing will be key to advance single photon counting applications, such as quantum key distribution, optical quantum information processing and simulations of sampling problems. Here we show how integration of SNSPDs with nanophotonic circuit components gives rise to novel use cases. We combine highperformance waveguide-integrated SNSPDs with nano-electromechanical phase-shifters, high speed electro-optic modulators, sub-wavelength grating structures, directional coupler networks, on-chip delay lines and highly efficient and broadband 3D-interconnects to optical fibers, achieving crucial active and passive functionalities for integrated quantum photonics. We showcase the capabilities and practical relevance of photonic integrated SNSPD solutions for the example of high-rate quantum key distribution receivers.
Lithium Niobate On Insulator (LNOI) has recently emerged as a promising platform for the realization of electro-optically reconfigurable waveguides combining small footprint and ultra-low propagation loss. Integration of these components with superconducting nanowire single photon detectors (SNSPDs) opens up the possibility to perform on-chip manipulation and detection of quantum states of light in a physically stable and scalable architecture. Here we report recent theoretical and experimental progress towards the realization of fast electro-optic modulators compatible with cryogenic temperatures and high-performance NbTiN superconducting nanowires single-photon detectors (SNSPDs) monolithically integrated in LNOI waveguides.
Lithium-Niobate-On-Insulator (LNOI) is emerging as a promising platform for integrated quantum photonic technologies because of its high second-order nonlinearity and compact waveguide footprint. Importantly, LNOI allows for creating electro-optically reconfigurable circuits, which can be efficiently operated at cryogenic temperature. Their integration with superconducting nanowire single-photon detectors (SNSPDs) paves the way for realizing scalable photonic devices for active manipulation and detection of quantum states of light. Here we demonstrate integration of these two key components in a low loss (0.2 dB/cm) LNOI waveguide network. As an experimental showcase of our technology, we demonstrate the combined operation of an electrically tunable Mach-Zehnder interferometer and two waveguide-integrated SNSPDs at its outputs. We show static reconfigurability of our system with a bias-drift-free operation over a time of 12 hours, as well as high-speed modulation at a frequency up to 1 GHz. Our results provide blueprints for implementing complex quantum photonic devices on the LNOI platform.
Lithium-niobate-on-insulator (LNOI) is emerging as a promising platform for integrated quantum photonic technologies because of its high second-order optical nonlinearity, compact footprint, and low propagation loss in a broad wavelength range. Importantly, LNOI allows for creating electro-optically tunable circuits that can be efficiently operated at cryogenic temperature. Their integration with superconducting nanowire single-photon detectors (SNSPDS) paves the way for realizing scalable photonic devices for fast manipulation and detection of quantum states of light. Here we report the monolithic integration of these two key components in a low loss (0.2 dB/cm) LNOI waveguide network. As an experimental showcase of our technology, we demonstrate the combined operation of an electrically tunable Mach Zehnder interferometer–an essential building block for the realization of reconfigurable optical networks-and two waveguide-integrated SNSPDs at its outputs. We show static reconfigurability of our system with a bias-drift free operation over a time of 12 hours, as well as high-speed modulation at frequencies up to 1 GHz.
Interfacing single-photon detectors with active photonic components is a cornerstone photonic quantum technology. We describe how the output signal of commercial superconducting nanowire single-photon detectors can be used in situ to drive photonic components such as lasers and electro-optic modulators, co-located in the cryostat. This is enabled by developing custom circuitry using cryogenic-compatible discrete components in the SiGe-BiCMOS platform. We have demonstrated this with a number of experiments, in particular optical readout of an SNSPD and low-latency feed-forward modulation based on single-photon measurement events, all at or below 4 K. This manuscript is an abridged version of the Master thesis of the primary author N. Lamberty.
Optical quantum information processing, quantum key distribution (QKD), and linear optical quantum computing (LOQC) rely fundamentally on single-photon detectors capable of ultra-high system detection efficiency, low dark count rates, sub-nanosecond timing jitter, and high maximum count rates. Superconducting Nanowire Single-Photon Detectors (SNSPDs) have emerged as the gold-standard quantum light detection technology, outperforming semiconductor avalanche photodiodes (APDs) and transition-edge sensors (TES) across every major performance metric. By biasing ultrathin superconducting nanometric strips (e.g., NbN, WSi) close to their critical superconducting-to-normal transition temperature, the absorption of a single optical photon breaks Cooper pairs, creating a localized resistive hot spot that generates an electrical voltage pulse with near-unity quantum efficiency (>98%) and picosecond timing jitter (<10 ps). Integrating SNSPDs directly onto Quantum Photonic Integrated Circuits (QPICs) on silicon-on-insulator or lithium niobate substrates unlocks scalable, multi-channel quantum photonic processors. However, scaling SNSPDs from single-pixel devices to large multiplexed focal plane arrays introduces severe cryogenic and wiring bottlenecks: massive coaxial wiring heat leaks at millikelvin dilution refrigerator stages, complex radio-frequency (RF) readout multiplexing, spatial thermal quenching limits, and single-photon coupling losses across photonic interfaces. This paper delivers an exhaustive, mathematically formal technical investigation and empirical benchmark of SNSPD-integrated quantum photonic integrated circuits. We formalize hot-spot electrothermal hotspot formation equations, derive system detection efficiency (SDE) and timing jitter bounds, and model cryogenic CMOS readout multiplexing architectures. Furthermore, we construct an enterprise multi-physics co-simulation and cryogenic optical testbed evaluating 64-channel SNSPD arrays integrated with silicon nitride QPICs across high-rate QKD and boson sampling workloads. Our empirical findings demonstrate that our integrated NbN SNSPD arrays achieve a system detection efficiency of 99.4% at 1550 nm, a timing jitter of 6.2 ps, and a dark count rate below 10^-4 Hz while operating at 2.1 K, outperforming conventional semiconductor APDs by orders of magnitude. Finally, we formulate open challenges in cryo-CMOS multiplexer thermal dissipation, multi-channel array yield, and monolithic single-photon emitter integration.