Advances in quantum computing pose significant threats to the security of conventional encryption standards. Although quantum key distribution systems offer inherent security, they face challenges in achieving practical secret-key rates over long transmission distances. Photonic Integrated Circuit technologies provide scalability and system efficiency for high key rates using multiplexed time-bin protocols. We present the architecture of a 16-channel multiplexed QKD system at a GHz clock rate realized on integrated photonic chips, promising further scalability. The sender module revolves around an indium-phosphide chip featuring tunable lasers, modulators, and combiners. On the receiver side, low fiber-to-chip coupling loss and waveguide-integrated superconducting nanowire single-photon detectors on silicon nitride provide the necessary detection efficiency.
Advances in quantum computing pose significant threats to the security of conventional encryption standards. Although quantum key distribution systems offer inherent security, they face challenges in achieving practical secret-key rates over long transmission distances. Photonic Integrated Circuit technologies provide scalability and system efficiency for high key rates using multiplexed time-bin protocols. We present the architecture of a 16-channel multiplexed QKD system at a GHz clock rate realized on integrated photonic chips, promising further scalability. The sender module revolves around an indium-phosphide chip featuring tunable lasers, modulators, and combiners. On the receiver side, low fiber-to-chip coupling loss and waveguide-integrated superconducting nanowire single-photon detectors on silicon nitride provide the necessary detection efficiency.
Quantum key distribution (QKD) enables secure communication even in the presence of advanced quantum computers. However, scaling up discrete-variable QKD to high key rates remains a challenge due to the lossy nature of quantum communication channels and the use of weak coherent states. Photonic integration and massive parallelization are crucial steps toward the goal of high-throughput secret-key distribution. We present a fully integrated photonic chip on silicon nitride featuring a four-channel wavelength-division demultiplexed QKD receiver circuit including state-of-the-art waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). With a proof-of-principle setup operated at a clock rate of 3.35 GHz, we achieve a total secret-key rate of up to 12.17 Mbit/s at 10 dB channel attenuation with low detector-induced error rates. The QKD receiver architecture is massively scalable and constitutes a foundation for high-rate many-channel QKD transmission.
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.
Quantum key distribution (QKD) is nowadays a well established method for generating secret keys at a distance in an information-theoretic secure way, as the secrecy of QKD relies on the laws of quantum physics and not computational complexity. In order to industrialize QKD, low-cost, mass-manufactured and practical QKD setups are required. Hence, photonic and electronic integration of the sender's and receiver's respective components is currently in the spotlight. Here we present a high-speed (2.5 GHz) integrated QKD setup featuring a transmitter chip in silicon photonics allowing for high-speed modulation and accurate state preparation, as well as a polarization-independent low-loss receiver chip in aluminum borosilicate glass fabricated by the femtosecond laser micromachining technique. Our system achieves raw bit error rates, quantum bit error rates and secret key rates equivalent to a much more complex state-of-the-art setup based on discrete components.
Integrated photonics provides a route to both miniaturization of quantum key distribution (QKD) devices and enhancing their performance. A key element for achieving discrete-variable QKD is a single-photon detector. It is highly desirable to integrate detectors onto a photonic chip to enable the realization of practical and scalable quantum networks. We realize a heterogeneously integrated, superconducting silicon-photonic chip. Harnessing the unique high-speed feature of our optical waveguide-integrated superconducting detector, we perform the first optimal Bell-state measurement (BSM) of time-bin encoded qubits generated from two independent lasers. The optimal BSM enables an increased key rate of measurement-device-independent QKD (MDI-QKD), which is immune to all attacks against the detection system and hence provides the basis for a QKD network with untrusted relays. Together with the time-multiplexed technique, we have enhanced the sifted key rate by almost one order of magnitude. With a 125-MHz clock rate, we obtain a secure key rate of 6.166 kbps over 24.0 dB loss, which is comparable to the state-of-the-art MDI-QKD experimental results with a GHz clock rate. Combined with integrated QKD transmitters, a scalable, chip-based, and cost-effective QKD network should become realizable in the near future.
Quantum key distribution (QKD) is a quantum communication technology that offers absolute security. Among its various implementations, continuous-variable (CV) QKD has garnered significant attention due to its high secret key generation rates and compatibility with conventional optical telecommunication infrastructure, which operates under ambient conditions. However, chip-based integration is crucial for realizing practical and scalable CV-QKD networks, and photonic integrated circuit technology is a potential solution, leveraging the on-chip integration of essential optical components onto silicon photonic circuits. Therefore, this work presents a compact, stable, and cost-effective quantum photonic CV-QKD system on a chip. Our architecture combines time- and polarization-multiplexing with high-extinction-ratio pulse generation to mitigate excess noise. At the same time, a real-time feedback control mechanism compensates for polarization drift, ensuring robust system performance. Fiber-based evaluations reveal secret key generation rates of 2.55 Mbps over 25 km and 0.737 Mbps over 50 km with 12 h stable operation, establishing, to our knowledge, a new benchmark for integrated photonic CV-QKD systems with both the transmitter and receiver on-chip. These results mark a significant milestone in on-chip quantum communication, paving the way for widespread adoption of photonic integrated circuits in future metropolitan quantum-secure networks.
Quantum key distribution (QKD) enables secure communication by harnessing the fundamental principles of quantum physics, which inherently guarantee information-theoretic security and intrinsic resistance to quantum computing attacks. However, the secure key rate of QKD typically decreases exponentially with increasing channel distance. In this work, by developing a novel polarization-state preparation method, an ultra-low time-jitter laser source and superconducting nanowire single-photon detectors, we demonstrate a 5-GHz integrated QKD system featuring ultra-low quantum bit error rates (QBERs). The system achieves secure key rates of 1.076 Mbps at 150 km and 105 kbps at 200 km over standard single-mode fiber channels, respectively. Our system substantially enhances the secure key rate, enabling high-resolution video calls with one-time-pad encryption over intercity backbone QKD links. This work represents a significant step forward in the development of high-performance practical QKD systems.