Integration of superconducting nanowire single-photon detectors with nanophotonic waveguides is a key technological step that enables a broad range of classical and quantum technologies on chip-scale ...platforms. The excellent detection efficiency, timing and noise performance of these detectors have sparked growing interest over the last decade and have found use in diverse applications. Almost 10 years after the first waveguide-coupled superconducting detectors were proposed, here, we review the performance metrics of these devices, compare both superconducting and dielectric waveguide material systems and present prominent emerging applications.
Abstract
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.
Quantum-photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single-photon detectors, show great potential for photonic quantum information ...processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second-order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming majority of linear optic experiments using bulk components, but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here, we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second-order nonlinearity in an aluminum-nitride microring resonator. We show the potential of our source for quantum information processing by measuring the high visibility anti-bunching of heralded single photons with nearly ideal state purity. Our down-conversion source yields measured coincidence rates of 80 Hz, which implies MHz generation rates of correlated photon pairs. Low noise performance is demonstrated by measuring high coincidence-to-accidental ratios. The generated photon pairs are spectrally far separated from the pump field, providing great potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single-photon detectors.
Abstract
Quantum key distribution (QKD) can greatly benefit from photonic integration, which enables implementing low-loss, alignment-free, and scalable photonic circuitry. At the same time, ...superconducting nanowire single-photon detectors (SNSPD) are an ideal detector technology for QKD due to their high efficiency, low dark-count rate, and low jitter. We present a QKD receiver chip featuring the full photonic circuitry needed for different time-based protocols, including single-photon detectors. By utilizing waveguide-integrated SNSPDs we achieve low dead times together with low dark-count rates and demonstrate a QKD experiment at 2.6 GHz clock rate, yielding secret-key rates of 2.5 Mbit/s for low channel attenuations of 2.5 dB without detector saturation. Due to the broadband 3D polymer couplers the reciver chip can be operated at a wide wavelength range in the telecom band, thus paving the way for highly parallelized wavelength-division multiplexing implementations.
Silicon photonics has offered a versatile platform for the recent development of integrated optomechanical circuits. However, silicon is limited to wavelengths above 1.1 μm and does not allow device ...operation in the visible spectrum range where low-noise lasers are conveniently available. The narrow bandgap of silicon also makes silicon optomechanical devices susceptible to strong two-photon absorption and free carrier absorption, which often introduce strong thermal effects that limit the devices' stability and cooling performance. Further, silicon also does not provide the desired lowest order optical nonlinearity for interfacing with other active electrical components on a chip. On the other hand, aluminum nitride (AlN) is a wide-band semiconductor widely used in micromechanical resonators due to its low mechanical loss and high electromechanical coupling strength. In this paper, we report the development of AlN-on-silicon platform for low loss, wide-band optical guiding, as well as its use for achieving simultaneously high-optical-quality-factor and high-mechanical-quality-factor optomechanical devices. Exploiting AlN's inherent second-order nonlinearity we further demonstrate electro-optic modulation and efficient second harmonic generation in AlN photonic circuits. Our results suggest that low-cost AlN-on-silicon photonic circuits are excellent substitutes for complementary metal-oxide-semiconductor-compatible photonic circuits for building new functional optomechanical devices that are free from carrier effects.
We demonstrate second order optical nonlinearity in a silicon architecture through heterogeneous integration of single-crystalline gallium nitride (GaN) on silicon (100) substrates. By engineering ...GaN microrings for dual resonance around 1560 nm and 780 nm, we achieve efficient, tunable second harmonic generation at 780 nm. The χ2 nonlinear susceptibility is measured to be as high as 16 ± 7 pm/V. Because GaN has a wideband transparency window covering ultraviolet, visible and infrared wavelengths, our platform provides a viable route for the on-chip generation of optical wavelengths in both the far infrared and near-UV through a combination of χ2 enabled sum-/difference-frequency processes.
Optical neural networks (ONNs) hold great potential for faster and more energy‐efficient information processing in coherent photonic circuits. To realize ONNs, linear combinations and nonlinear ...activation functions have to be implemented in an optical fashion. Optical nonlinearities are, however, still difficult to achieve, and existing designs are usually too inflexible to offer different activation functions as used in artificial neural networks. Herein, the nonlinear properties of the large and highly adaptive class of photoswitchable chemical compounds is made accessible as activation functions in ONNs by employing photo‐induced isomerization in azobenzenes to steer activation behavior through nonlinear modulation of an information‐carrying optical signal. The strength of the nonlinearity can be controlled by the chemical concentration while a physically motivated model describes the experimental data for systematically varied photoswitching parameters, resulting in a tunable yet interpretable activation function. Employing such an activation function in a neural network then allows to gauge its strength and perform established classification tasks. The work combines recent advances with photoswitchable chemical compounds and optical neural networks to enable control over the design of nonlinear activation functions, thus opening exciting perspectives for explaining the emergence of intelligent behavior in neural networks.
Photo‐induced isomerization of molecular compounds is utilized as a tunable photonic nonlinearity for optical neural networks (ONNs) applied in image classification demonstrating the general eligibility of photochemical activation functions to overcome the absence of efficient nonlinear building blocks in ONNs.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Photonic integrated circuits hold great potential for realizing quantum technology. Efficient single-photon detectors are an essential constituent of any such quantum photonic implementation. In this ...regard waveguide-integrated superconducting nanowire single-photon detectors are an ideal match for achieving advanced photon counting capabilities in photonic integrated circuits. However, currently considered material systems do not readily satisfy the demands of next generation nanophotonic quantum technology platforms with integrated single-photon detectors, in terms of refractive-index contrast, band gap, optical nonlinearity, thermo-optic stability and fast single-photon counting with high signal-to-noise ratio. Here we show that such comprehensive functionality can be realized by integrating niobium titanium nitride superconducting nanowire single-photon detectors with tantalum pentoxide waveguides. We demonstrate state-of-the-art detector performance in this novel material system, including devices showing 75% on-chip detection efficiency at tens of dark counts per second, detector decay times below 1 ns and sub-30 ps timing accuracy for telecommunication wavelengths photons at 1550 nm. Notably, we realize saturation of the internal detection efficiency over a previously unattained bias current range for waveguide-integrated niobium titanium nitride superconducting nanowire single-photon detectors. Our work enables the full set of high-performance single-photon detection capabilities on the emerging tantalum pentoxide-on-insulator platform for future applications in integrated quantum photonics.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Nanophotonics holds great promise for integrated quantum technologies, but realizing all functionalities for processing quantum states of light in optical waveguides poses an outstanding challenge. ...Here we show that tantalum pentoxide-on-insulator offers significant advantages for such purpose and experimentally demonstrate crucial photonic integrated circuit components. Exploiting advanced nanophotonic design and state-of-the-art nanofabrication processes, we realize low-loss waveguiding with 1 dB/cm propagation loss, efficient optical fiber-chip interfaces with more than 100 nm bandwidth, micro-ring resonators with quality factors of 357,200 and tunable directional couplers. We further achieve active functionality with nano-electromechanical phase-shifters. Our work enables reconfigurable photonic circuit configurations in the Ta
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material system with highly favorable optical properties for integrated quantum photonics.
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