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.
We realize fast, efficient and small footprint niobium nitride superconducting nanowire single photon detectors atop of photonic waveguides. By reducing the bias current of the nanowire, in order to break the superconductivity and trigger a detection event, more than one photon needs to be absorbed in a localized section of the wire within a very short time delay (hot-spot relaxation time), making such devices promising also for multiphoton sensing applications. We adopt a near-infrared pump-probe technique in a cryogenic environment to investigate the bias current dependence of the hot-spot relaxation time. A minimum relaxation time of (22 ± 1) ps is obtained when applying a bias current of 50% of the switching current at a bath temperature of 1.7K. Our study reveals a strong increase of the picosecond relaxation time with increasing bias current. We further adopt the same technique for determining the multi-photon detection regimes of the detector, which are in agreement with standard quantum detector tomography. In this context, we introduce a practical model and reconstruction method for determining the detector sensitivity regimes. Our work provides a complete description of the detector working operation in both number photon threshold sensitivity and time-delay sensitivity. The results allow for implementing on-chip measurement architectures for the characterization of weak classical light emitters and fast single photon sources with only one detector, driven at different biasing currents, with a drastic reduction of the time uncertainty limitations of typical correlation measurement systems.
Nanophotonic integrated circuits are emerging as a promising platform for quantum photonics. A key building block are waveguide integrated detectors with superior performance. Detectors based on superconductor nanowires (SNSPDs) attached to optical waveguides have been shown to provide high efficiency and good timing performance, as well as broad bandwidth. To move towards applications in high bandwidth quantum communication and processing, ultrafast single-photon detectors with high efficiency are needed. The speed of meander type SNSPDs is limited because the required high absorption efficiency necessitates long nanowires deposited on top of the waveguide. This enhances the kinetic inductance and makes the detectors slow. We overcome this problem by aligning the nanowire perpendicular to the waveguide to realize devices with a length below 1 µm. By integrating the nanowire into a photonic crystal cavity, we recover high absorption efficiency, thus enhancing the detection efficiency by more than an order of magnitude. Our cavity enhanced superconducting nanowire detectors are fully embedded in silicon nanophotonic circuits and efficiently detect single photons at telecom wavelengths. The detectors possess sub-nanosecond decay (~ 120 ps) and recovery times (~ 510 ps), and thus show potential for GHz count rates at low timing jitter (~ 32 ps).
Quantum photonic circuits based on nanophotonic components hold promise for overcoming scalability limitations in optical quantum systems. Functional systems will require the co-integration of single photon sources, detectors and tunable photonic components. Waveguide integrated single photon detectors based on superconducting nanowires (SNSPDs) have been shown to fulfill the demanding requirements for on-chip quantum photonics. Because they provide very wide optical detection bandwidth, their use with optically pumped single photon sources poses severe challenges for on-chip filtering. We overcome these challenges by co-integrating electrically driven single photon sources with superconducting detectors. Single photon sources with nanoscale footprint are realized by depositing electrically contacted carbon nanotubes (CNTs) across nanophotonic waveguides. CNTs under electrical current bias are shown to emit non-classical light which is coupled efficiently into the underlying photonic framework. The CNTs are shown to provide high count rates in the MHz range. The statistical characterization of the CNT light source crucially relies on the high timing resolution of the SNSPDs which allows for measuring photon statistics for emitters with sub-100ps lifetime. The combination of top-down nanofabrication with deposition by electrophoresis provides a waferscale approach for realizing non-classical circuits on chip. Such hybrid quantum photonic devices therefore hold promise for realizing complex integrated devices without additional optical input ports.
We report on the design, fabrication and measurement of travelling-wave superconducting nanowire single-photon detectors (SNSPDs) integrated with polycrystalline diamond photonic circuits. We analyze their performance both in the near-infrared wavelength regime around 1600 nm and at 765 nm. Near-IR detection is important for compatibility with the telecommunication infrastructure, while operation in the visible wavelength range is relevant for compatibility with the emission line of silicon vacancy centers in diamond which can be used as efficient single-photon sources. Our detectors feature high critical currents (up to 31 μA) and high performance in terms of efficiency (up to 74% at 765 nm), noise-equivalent power (down to 4.4×10-19 W/Hz1/2 at 765 nm) and timing jitter (down to 23 ps).
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