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.
Quantum photonics has emerged as a key driver for advancing applications, such as quantum communication and sensing, that harness the potential of quantum effects beyond classical capabilities. Photonic integrated circuits favor such implementations by providing low loss and interferometric stability. Nonetheless, to fully leverage these advantages, two major challenges need to be addressed: highly efficient fiber-to-chip light coupling and waveguide-integrated single-photon detection. In this work, we utilize subwavelength grating (SWG) metamaterials to design (i) novel off-chip couplers enabling sub-decibel coupling efficiency and (ii) a new superconducting nanowire single-photon detector (SNSPD) concept featuring enhanced photon absorption and fast detection.
Quantum technologies and optical sensors with ultimate sensitivity require efficient counting of single photons. Superconducting nanowire single-photon detectors have set leading performance benchmarks in this regard but evolving from stand-alone fiber-coupled detectors to highly integrated receivers with large numbers of photonic channels and configurable optical functionalities has remained a challenge. Here we show how large numbers of superconducting nanowire single-photon detectors with high detection efficiency and low timing jitter can be integrated with nanophotonic circuits. The latter allow for combining photon counting capabilities of superconducting nanowires with active and passive optical control functionalities, such as switching, phase shifting and photon number resolution, which we demonstrate for leading photonic integrated circuit platforms. Broadband optical interconnects produced in 3D direct laser writing enable competitive system detection efficiency, which we can reproduce in a receiver unit that integrates 64 individually addressable superconducting nanowire single-photon detectors. We show that the system is well-suited for massively parallelized quantum key distribution, achieving secret key generation rates beyond 10 Mbit/sec in a field test. Integrating large numbers of superconducting nanowire single photon detectors with optical waveguides on configurable nanophotonic chips offers a wide range of applications in quantum communication, information processing and sensing.
We demonstrate the integration of solid-state single-photon sources in nanophotonic waveguides and show how photons can be collected from several such emitters simultaneously. A lithographic technique here allows us to position solution-based colloidal quantum dots or nanodiamonds hosting defect centers with tens of nanometer accuracy within nanophotonic devices at chip-scale. We further present a novel reinforcement learning-based inverse design approach for realizing photonic integrated circuit components that enable the efficient manipulation of optical modes in devices with minimal footprint. Combining single-photon sources and circuits on a nanophotonic chip will benefit a wide range of applications in quantum technology.
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.
With recent advances in quantum technologies for applications such as communication, cryptography, computing, metrology and sensing, the performance and scalability of single-photon detection as a vital key component is becoming increasingly important. At the same time, ongoing efforts in the development of high-performance photonic integrated circuits (PIC) benefit the miniaturization and scalability of these quantum technologies. Waveguide-integrated superconducting nanowire single-photon detectors (WI-SNSPDs) allow to combine excellent performance metrics, such as high detection efficiency, low dark-count rates and low timing jitter below 20 ps with the scalability and functionality that PIC platforms such as Si3N4 provide. We have previously demonstrated broadband efficient single-photon detection with a single device over a range from visible to mid-infrared wavelengths and ultra-fast detector recovery times allowing for up to GHz count rates. Here, we present the utilization of WI-SNSPDs for discrete-variable quantum cryptography receivers with the complete photonic circuitry embedded together with the single-photon detectors on a single silicon chip, where the secret-key rates greatly benefit from the short recovery times of the detectors especially for metropolitan distances. We further realize a fully packaged 64 channel WI-SNSPD matrix for use in a wavelengthdivision multiplexed QKD setup.
KEYWORDS: Photodetectors, Sensors, Photonics systems, Data processing, Chemical elements, Temporal resolution, Superconductors, Single photon detectors, Single photon, Quantum information
One key challenge in transferring single-photon based quantum technologies from a laboratory environment ‘into the field’ are the limited count rates achievable with today's hardware based on individual detection units. To overcome this limitation we have developed key components pushing beyond the bandwidth-limit of single devices with a massively parallelized (x64) single-photon detection system. Here, detector elements based on superconducting nanowires are optimized for lowest reset times and highest temporal resolution. On-chip (FPGA) data processing over all detector channels provides a viable solution to pre-process the potentially massive amount of initial data which is demonstarted in a QKD experiment.
Upcoming quantum technologies require scalable and cost-efficient technical solutions for widespread functionality. In order to exploit the quantum states of light, single-photon detectors are essential for application. Here, we present a low-footprint plug-and-play multi-channel single-photon detector system featuring integrated photonics that allows for ultra-fast quantum key distribution (QKD). Each channel comprises a superconducting nanowire single-photon detector (SNSPD) patterned from a niobium-titanium nitride (NbTiN) superconducting film atop silicon nitride waveguide structures. Subsequently, the on-chip photonics are interfaced by broadband 3D polymeric fiber-to-chip couplers to the ports of an 8x8 fiber array. The readout electronics allow for individual evaluation of up to 64 channels simultaneously. Integrated to a QKD experiment, a pair of the system's detection channels achieves secret key rates of up to 2.5 Mbit/s employing a coherent one-way protocol.
The integration of nano-scale quantum emitters with nano-photonic circuits is a prerequisite for a broad range of quantum technologies, benefitting quantum communication, quantum sensing or quantum information processing. However, the assembly of single emitters with high positioning accuracy in large-scale arrays and their efficient interfacing with photonic quantum channels constitutes a major challenge. Here, we show how single colloidal core-shell quantum dots (CQDs) are embedded in photonic integrated circuits that allow for individual excitation and photoluminescence collection. By utilizing finite-difference time-domain simulations, we design nanophotonic interfaces with high coupling efficiencies between CQDs and single-mode optical waveguides. Here, we utilize a tantalum pentoxide (Ta2O5) on insulator nanophotonic platform that enables integrated optics experiments at the single-photon level due to low intrinsic material fluorescence and low-loss waveguiding. We employ a PMMA thin film for patterning hundreds of nanoscale apertures that are precisely aligned to prefabricated nanophotonic devices and transfer a solution of CdSeTe/ZnS CQDs diluted in decane into the apertures. The CQDs are positioned with 50 nm accuracy with respect to optical waveguides. Highly efficient 3D fiber-chip interfaces produced from a polymer in direct laser writing allow us to characterize the CQDwaveguide coupling and assess the spectral characteristics of the collected photoluminescence. Moreover, we record the second order autocorrelation function g2(τ) of the photoluminescence signal, which shows photon antibunching indicative of individual quantum emitters. Addressing individual CQDs via independent waveguide channels and a reproducible integration approach that extends to larger numbers of devices provides a novel perspective for realizing quantum technology with solution-processible single-photon emitters.
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