Integrated photonic quantum information processing (QIP) has advanced rapidly due to progress in various nanophotonic platforms. Single photon detectors have been the subject of intense study due to their ubiquity in QIP systems, yet many state-of-the art detectors operate at cryogenic temperatures under vacuum and suffer from long dead times. We propose and demonstrate a single photon detection scheme based on optical parametric amplification in nanophotonic lithium niobate (LN) combined with a classical photodetector. We use quantum detector tomography and experimentally demonstrate an efficiency of 26.5% with a 2.2% dark count rate. We show that by improving the nonlinearity-to-loss ratio in nanophotonics and using homodyne detection on a squeezed pump, the detector can achieve 69% efficiency with 0.9% dark count rate. The detector operates at room temperature, has no intrinsic dead time, and is readily integrated in LN nanophotonics, in which many other components of photonic QIP are available. Our results represent a step towards all-optical ultrafast photon detection for scalable nanophotonic QIP.
Integrated photonic quantum information processing (QIP) has advanced rapidly due to progress in various nanophotonic platforms. Single photon detectors have been the subject of intense study due to their ubiquity in QIP systems, yet many state-of-the art detectors operate at cryogenic temperatures under vacuum and suffer from long dead times. We propose and demonstrate a single photon detection scheme based on optical parametric amplification in nanophotonic lithium niobate (LN) combined with a classical photodetector. We use quantum detector tomography and experimentally demonstrate an efficiency of 26.5% with a 2.2% dark count rate. We show that by improving the nonlinearity-to-loss ratio in nanophotonics and using homodyne detection on a squeezed pump, the detector can achieve 69% efficiency with 0.9% dark count rate. The detector operates at room temperature, has no intrinsic dead time, and is readily integrated in LN nanophotonics, in which many other components of photonic QIP are available. Our results represent a step towards all-optical ultrafast photon detection for scalable nanophotonic QIP.
Photonics offers the potential for large-scale, room-temperature, and ultrafast quantum operations. Multiplexing pulses of light allows for high throughput speeds and dense encoding, with tens of thousands of optical modes being present in a time as short as a microsecond. However, the measurement speed of electronic devices such as photodetectors is currently one bottleneck in such time-multiplexed scalability, because many quantum optical protocols rely on measurement, including state preparation, feed-forward, and feedback. Furthermore, characterization of quantum states and modes is essential for their effective use. Using nanophotonic optical parametric amplifiers (OPAs) presents one way to circumvent the measurement limitations of current quantum photonic schemes. Their large amplification bandwidth, enabled by dispersion engineering on nanophotonic integrated platforms, allows information encoded in femtosecond-scale, THz-bandwidth, multimode quantum optical states to be accessed with nonlinear optical interactions. In this work, we show how ultra-broadband integrated nanophotonic OPAs can be used to measure ultrafast and multimode quantum states of light. First, we explore the single-photon detection capabilities of OPAs, showing that current OPAs operating in the Gaussian regime are capable of 250 MHz photon count rates with 26% efficiency and a 2% dark count probability. We also show how non-Gaussian operation through pump depletion, with performance that approaches state-of-the-art photon detectors in terms of efficiency and dark count rate while retaining ultrafast operation, can become experimentally possible with a higher nonlinear coupling rate and lower loss. Next, we use nanophotonic OPAs to both generate and characterize multimode ultrafast squeezed vacuum. We use the photocurrent distribution of amplified squeezed vacuum to recover 2.41 dB of squeezing in one mode of a 154-fs multimode squeezed pulse and reconstruct its Wigner distribution. Finally, we investigate the capabilities of broadband nanophotonic OPAs to determine the temporal mode structure and quadrature variances of ultra-broadband temporally multimode quantum states by adapting frequency-resolved optical gating to the quantum regime. We numerically show the successful full characterization of a multimode squeezed state, even in the presence of noise. Together, these results establish OPAs as a valuable measurement device for measuring ultrafast quantum pulses and learning the structure of multimode quantum states, and they provide one building block towards a framework for scalable continuous-variable quantum photonics in which state generation, manipulation, and characterization occur within the same nanophotonic platform.
Squeezed vacuum, a fundamental resource for continuous-variable quantum information processing, has been used to demonstrate quantum advantages in sensing, communication, and computation. While most experiments use homodyne detection to characterize squeezing and are therefore limited to electronic bandwidths, recent experiments have shown optical parametric amplification (OPA) to be a viable measurement strategy. Here, we realize OPA-based quantum state tomography in integrated photonics and demonstrate the generation and all-optical Wigner tomography of squeezed vacuum in a nanophotonic circuit. We employ dispersion engineering to enable the distortion-free propagation of femtosecond pulses and achieve ultrabroad operation bandwidths, effectively lifting the speed restrictions imposed by traditional electronics on quantum measurements with a theoretical maximum clock speed of 6.5 THz. We implement our circuit on thin-film lithium niobate, a platform compatible with a wide variety of active and passive photonic components. Our results chart a course for realizing all-optical ultrafast quantum information processing in an integrated room-temperature platform.
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.
Ultra-Short Pulse Biphoton Source in Lithium Niobate Nanophotonics at 2μm
Photonics offers unique capabilities for quantum information processing (QIP) such as room-temperature operation, the scalability of nanophotonics, and access to ultrabroad bandwidths and consequently ultrafast operation. Ultrashort-pulse sources of quantum states in nanophotonics are an important building block for achieving scalable ultrafast QIP, however, their demonstrations so far have been sparse. Here, we demonstrate a femtosecond biphoton source in dispersion-engineered periodically poled lithium niobate nanophotonics. We measure 17 THz of bandwidth for the source centered at 2.09 \textmu m, corresponding to a few optical cycles, with a brightness of 8.8 GHz/mW. Our results open new paths towards realization of ultrafast nanophotonic QIP.
Photonics offers unique capabilities for quantum information processing (QIP) such as room-temperature operation, the scalability of nanophotonics, and access to ultrabroad bandwidths and consequently ultrafast operation. Ultrashort pulse sources of quantum states in nanophotonics are an important building block for achieving scalable ultrafast QIP; however, their demonstrations so far have been sparse. Here, we demonstrate a femtosecond biphoton source in dispersion-engineered periodically poled lithium niobate nanophotonics. We measure 17 THz of bandwidth for the source centered at 2.09 µm, corresponding to a few optical cycles, with a brightness of 8.8 GHz/mW. Our results open new paths toward realization of ultrafast nanophotonic QIP.
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.