As quantum key distribution (QKD) begins to move from laboratories into real-world use cases, some practical aspects need to be addressed before it can be widely adopted. Not least of which is the size and cost of the devices. The semiconductor industry, over the last 50 years, has provided a scalable platform for integrated electronics. Using the same fabrication processes, it is possible to create quantum photonic microchips to entirely replace the optical components needed for QKD. Using both indium phosphide and silicon devices, we can design and fabricate integrated devices to perform QKD with highly competitive speeds and error rates. At the same time, they offer dramatically reduced power requirements, size and costs while offering increased phase stability and inherent scalability. Other recent developments in the field include new protocols to remove the security assumptions about the physical devices used. One such protocol is measurement-device independent QKD (MDI-QKD) which removes all detector side-channels. Combining integrated devices with MDI-QKD, we are working towards developing a practical architecture for metropolitan QKD. Here, we provide a recap of QKD and discuss the current state of integrated QKD devices and their potential applications in metropolitan networks.
As quantum key distribution (QKD) begins to move from laboratories into real-world use cases, some practical aspects need to be addressed before it can be widely adopted. Not least of which is the size and cost of the devices. The semiconductor industry, over the last 50 years, has provided a scalable platform for integrated electronics. Using the same fabrication processes, it is possible to create quantum photonic microchips to entirely replace the optical components needed for QKD. Using both indium phosphide and silicon devices, we can design and fabricate integrated devices to perform QKD with highly competitive speeds and error rates. At the same time, they offer dramatically reduced power requirements, size and costs while offering increased phase stability and inherent scalability. Other recent developments in the field include new protocols to remove the security assumptions about the physical devices used. One such protocol is measurement-device independent QKD (MDI-QKD) which removes all detector side-channels. Combining integrated devices with MDI-QKD, we are working towards developing a practical architecture for metropolitan QKD. Here, we provide a recap of QKD and discuss the current state of integrated QKD devices and their potential applications in metropolitan networks.
Quantum key distribution (QKD) is moving from laboratory demonstrations toward network deployment, and integrated photonic chips provide a hardware route for compact, stable and scalable systems. This review summarizes progress in integrated photonic chips for QKD from protocol requirements to deployable systems. It first examines how decoy-state BB84, measurement-device-independent QKD (MDI-QKD), twin-field QKD (TF-QKD), continuous-variable QKD (CV-QKD) and device-independent QKD (DI-QKD) constrain chip metrics such as loss, modulation accuracy, state indistinguishability, phase stability, synchronization and security monitoring. It then compares planar lightwave circuit (PLC), silicon photonics, silicon nitride, thin-film lithium niobate, indium phosphide (InP) and heterogeneous platforms in terms of routing loss, modulation speed, stable interference, source integration and detector interfaces. Transmitter and receiver architectures, coherent detection, single-photon detection interfaces and on-chip monitoring are discussed as system-level building blocks. The review further analyses phase stability, packaging coupling, thermal management, polarization control, network coexistence and reliability, emphasizing that deployable QKD chips must remain calibratable and compatible with security models under realistic operation. Finally, system demonstrations, network deployment and practical security are discussed within a unified evaluation framework. Throughout, we argue that integration benefits QKD only when compact routing, stable interference, calibration access and manufacturable packaging jointly keep the device inside the assumptions of its security proof; accordingly, chip performance should be judged by mapped, calibratable security parameters rather than by integration density alone.
Advances in quantum computing are a rapidly growing threat towards modern cryptography. Quantum key distribution (QKD) provides long-term security without assuming the computational power of an adversary. However, inconsistencies between theory and experiment have raised questions in terms of real-world security, while large and power-hungry commercial systems have slowed wide-scale adoption. Measurement-device-independent QKD (MDI-QKD) provides a method of sharing secret keys that removes all possible detector side-channel attacks which drastically improves security claims. In this Letter, we experimentally demonstrate a key step required to perform MDI-QKD with scalable integrated devices. We show Hong-Ou-Mandel interference between weak coherent states carved from two independent indium phosphide transmitters at 431 MHz with a visibility of 46.5±0.8%. This Letter demonstrates the feasibility of using integrated devices to lower a major barrier towards the adoption of QKD in metropolitan networks.
Measurement-device-independent quantum key distribution (MDI QKD) removes all detector side channels and enables secure QKD with an untrusted relay.It is suitable for building a star-type quantum access network, where the complicated and expensive measurement devices are placed in the central untrusted relay and each user requires only a low-cost transmitter, such as an integrated photonic chip.Here, we experimentally demonstrate a 1.25-GHz silicon photonic chip-based MDI QKD system using polarization encoding.The photonic chip transmitters integrate the necessary encoding components for a standard QKD source.We implement random modulations of polarization states and decoy intensities, and demonstrate a finite-key secret rate of 31 bit=s over 36-dB channel loss (or 180-km standard fiber).This key rate is higher than state-of-the-art MDI QKD experiments.The results show that silicon photonic chipbased MDI QKD, benefiting from miniaturization, low-cost manufacture, and compatibility with CMOS microelectronics, is a promising solution for future quantum secure networks.
Quantum key distribution (QKD) can serve large numbers of users with unconditional secure communication, in which measurement-device-independent (MDI) QKD protocol can conveniently enhance realistic security by eliminating all detector side channels. In multi-user scenarios, MDI-QKD networks should meet the requirements of reliability and robustness. Around the issues, we complete a series of work on performance improvement, low-cost deployment, and robust networking. First is to answer how to change the trusted node to the untrusted node with low cost, here we propose and demonstrate an MDIQKD which is compatible with phase encoding BB84 networks, allowing for economical deployment of MDI-QKD networks and reconciliation between high key rate and high realistic security in the same network. Then we make the MDI networks more robust. We design an MDI-QKD networking scheme for multi-user access where more than two users can generate keys synchronously regardless of aligning reference frames and compensating channel disturbance on polarization. Third, we find a general method to distil secure keys from quantum discord, which is different to the previous entanglement-based frameworks of MDI-QKD, allowing imperfect preparation and measurement of quantum states. The series of work can help the practical application of MDI-QKD networks, and promote the development of quantum networks.
An industrial-scale adoption of Quantum Key Distribution (QKD) requires the development of practical, stable, resilient and cost-effective hardware that can be manufactured at large scales. In this work we present a high-speed (1.25GHz), field-deployable QKD prototype based on integrated photonics, that is consolidated into standard 19-inch rack compatible units. Through integrated photonics, the system prioritizes autonomous long-term stability in metropolitan settings. The architecture is further simplified by removing the need for chromatic dispersion compensation over metropolitan distances (below 100km). We demonstrate continuous key exchange over more than 4 km of metropolitan optical fiber, where the prototype maintained stable, uninterrupted operation across a measurement spanning more than 12 day-night cycles without manual intervention.
Improvement in secure transmission of information is an urgent need for governments, corporations and individuals. Quantum key distribution (QKD) promises security based on the laws of physics and has rapidly grown from proof-of-concept to robust demonstrations and deployment of commercial systems. Despite these advances, QKD has not been widely adopted, and large-scale deployment will likely require chip-based devices for improved performance, miniaturization and enhanced functionality. Here we report low error rate, GHz clocked QKD operation of an indium phosphide transmitter chip and a silicon oxynitride receiver chip-monolithically integrated devices using components and manufacturing processes from the telecommunications industry. We use the reconfigurability of these devices to demonstrate three prominent QKD protocols-BB84, Coherent One Way and Differential Phase Shift-with performance comparable to state-of-the-art. These devices, when combined with integrated single photon detectors, pave the way for successfully integrating QKD into future telecommunications networks.