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High-speed time-gated Single Photon Avalanche Photodiode (SPAD) allows faster detector response times and low afterpulsing effect. Due to the intrinsic capacitance of the SPAD, a fraction of the gate signal is coupled to the readout node. This is unwanted signal and needs to be suppressed. This paper presents a technique to recover the tiny avalanche signal, compensating the high-speed gate feedthrough. The cancellation is carried out in the same way as in the destructive scheme. However, the interfering signal was generated by combining two similar but out-of-phase sinusoidal signals. The proposed scheme is performed using a Micro Photon Devices (MPD) InGaAS/InP SPAD and a Printed Circuit Board (PCB) circuit that has been implemented for this purpose. Tests and measurements were conducted when applying 59.4 V fixed DC supply and 5 $\text{V}_{pp}~1.72$ GHz sinusoidal gating signal. The detector was cooled to 223.15 K, corresponding to 60.4 V breakdown voltage. Applying attenuated laser pulses at 1550 nm, a quantum efficiency of 16% has been measured. The developed technique allowed to suppress the SPAD capacitive response up to 50 dB. In addition, the scheme has provided a better avalanche signal quality compared to a similar circuit employing a low-pass filter to suppress the gate frequency.

The “quantum threat” to our current, convenient cryptographic algorithms is getting closer, with demonstrable progress by commercial quantum computing efforts. It is now more important than ever that we combine all of our tools into a new quantum-safe toolbox to develop the next generation of quantum-safe networking solutions. Here we combine an integrated quantum entropy source with quantum-resistant algorithms in the GnuGPG open-source software; leading to a fully quantum-safe version of GnuGPG. The quantum entropy source itself is capable of a raw rate of randomness in excess of 10 Gbps. After post-processing, quantum random numbers are used by the quantum-resistant algorithms to allow GnuGPG to perform its usual public-key cryptographic tasks, such as digitally signing documents, but now in a secure quantum-safe way.

Quantum key distribution (QKD) is a state-of-the-art method of generating cryptographic keys by exchanging single photons. Measurements on the photons are constrained by the laws of quantum mechanics, and it is from this that the keys derive their security. Current public key encryption relies on mathematical problems that cannot be solved efficiently using present-day technologies; however, it is vulnerable to computational advances. In contrast QKD generates truly random keys secured against computational advances and more general attacks when implemented properly. On the other hand, networks are moving towards a process of softwarization with the main objective to reduce cost in both, the deployment and in the network maintenance. This process replaces traditional network functionalities (or even full network instances) typically performed in network devices to be located as software distributed across commodity data centers. Within this context, network function virtualization (NFV) is a new concept in which operations of current proprietary hardware appliances are decoupled and run as software instances. However, the security of NFV still needs to be addressed prior to deployment in the real world. In particular, virtual network function (VNF) distribution across data centers is a risk for network operators, as an eavesdropper could compromise not just virtualized services, but the whole infrastructure.We demonstrate, for the first time, a secure architectural solution for VNF distribution, combining NFV orchestration and QKD technology by scheduling an optical network using SDN. A time-shared approach is designed and presented as a cost-effective solution for practical deployment, showing the performance of different quantum links in a distributed environment.

Modern communication strives towards provably secure systems which can be widely deployed. Quantum key distribution provides a methodology to verify the integrity and security of a key exchange based on physical laws. However, physical systems often fall short of theoretical models, meaning they can be compromised through uncharacterized side-channels. The complexity of detection means that the measurement system is a vulnerable target for an adversary. Here, we present secure key exchange up to 200 km while removing all side-channels from the measurement system. We use mass-manufacturable, monolithically integrated transmitters that represent an accessible, quantum-ready communication platform. This work demonstrates a network topology that allows secure equipment sharing which is accessible with a cost-effective transmitter, significantly reducing the barrier for widespread uptake of quantum-secured communication.

The security of sensitive information exchange has become a major topic in recent years. Quantum Key Distribution (QKD) provides a highly secure approach to share random encryption keys between two communication terminals. In contrast with traditional public cryptography methods, QKD security relies on the foundations of quantum mechanics and not on computational capabilities. This makes QKD unconditionally secure (if properly implemented) and it is envisaged as a main component in the next–generation cryptographic technology. QKD has already been successfully demonstrated in different contexts such as fibre-to- fibre, and free-space ground-toground as well as ground-to-air communications. However, Size, Weight and Power (SWaP) constraints have prevented previous implementations to be demonstrated on small form airborne platforms such as Unmanned Aircraft Systems (UAS) and High Altitude Pseudo-Satellites (HAPS). Project Q-DOS aims to deliver a QKD module using compact, cutting-edge photonic waveguide technology, which will allow low-SWaP aerospace requirements to be met. This module uses 1550 nm single photons to implement a BB84 protocol, and will enable the demonstration of a secure, high-speed optical communication data link (~0.5 Gbps) between a drone and a ground station. The targeted link range is 1 km. The airborne communications module, including the QKD terminal, tracking modules, traditional communications systems, optics and control electronics, must not exceed a mass of 5 kg and a power consumption of 20 W.

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 $46.5 \pm 0.8\%$. This work demonstrates the feasibility of using integrated devices to lower a major barrier towards adoption of QKD in metropolitan networks.

Chip-scale integrated quantum technologies provide new approaches to the generation, manipulation and detection of quantum states of light, and provide a means to deliver complex and compact quantum photonic circuits for applications in quantum communications.

Random numbers are a fundamental resource in science and technology. Among the different approaches to generating them, random numbers created by exploiting the laws of quantum mechanics have proven to be reliable and can be produced at enough rates for their practical use. While these demonstrations have shown very good performance, most of the implementations using free-space and fibre optics suffer from limitations due to their size, which strongly limits their practical use. Here we report a quantum random number generator based on phase fluctuations from a diode laser, where the other required optical components are integrated on a mm-scale monolithic silicon-on-insulator chip. The post-processing reported in this experiment is performed via software. However, our physical device shows the potential of operation at generation rates in the Gbps regime. Considering the device’s size, its simple, robust and low power operation, and the rapid industrial uptake of silicon photonics, we foresee the widespread integration of the reported design in more complex systems.

Quantum key distribution (QKD) is one of the most commercially-advanced quantum optical technologies operating in the single-photon regime. The commercial success of this disruptive technology relies on customer trust. Network device manufacturers have to meet stringent standards in order to ensure the operational security of their devices. The National Physical Laboratory (NPL) and the University of Bristol (Bristol) are working to produce a suite of tests to determine the operating characteristics and implementation security of chip-scale quantum devices designed for security purposes. These tests will inform and provide assurance to potential customers of such devices. Results from initial measurements performed on the Bristol chip-scale transmitter and receiver are presented, with the aim of informing the development of the system.

Optical homodyne detection has found use as a characterization tool in a range of quantum; technologies. So far implementations have been limited to bulk optics. Here we present the optical; integration of a homodyne detector onto a silicon photonics chip. The resulting device operates; at high speed, up 150 MHz, it is compact and it operates with low noise, quantified with 11 dB; clearance between shot noise and electronic noise. We perform on-chip quantum tomography of; coherent states with the detector and show that it meets the requirements for characterising more; general quantum states of light. We also show that the detector is able to produce quantum random; numbers at a rate of 1.2 Gbps generation rate, by measuring the vacuum state of the electromagnetic; field-the produced random numbers pass all the statistical tests provided by the NIST statistical; test suite.

We experimentally implement a compact and practical solution for wavelength-division multiplexed quantum key distribution using integrated photonics. This increases secret key rates and allows for greater operational flexibility to meet network user requirements.

We demonstrate, for the first time, a secure optical network architecture that combines NFV orchestration and SDN control with quantum key distribution (QKD) technology. A novel time-shared QKD network design is presented as a cost-effective solution for practical networks.

We present the first silicon-integrated homodyne detector suitable for characterising quantum states of light travelling in a silicon waveguide. We report high-fidelity quantum state tomography of coherent states. The device was also used to generate random numbers at a speed of 1.2 Gbps.

Silicon integrated quantum photonics has recently emerged as a promising approach to realising complex and compact quantum circuits, where entangled states of light are generated and manipulated on-chip to realise applications in sensing, communication and computation. Recent highlights include chip-to-chip quantum communications, programmable quantum circuits, chip-based quantum simulations and routes to scalable quantum information processing.

Silicon quantum photonics has emerged as a promising approach to realising complex and compact quantum circuits for applications in communication and computation. Highlights include chip-to-chip quantum communications, programmable quantum circuits and chip-based quantum simulations.

Chip-scale integrated quantum technologies provide new approaches to the generation, manipulation and detection of quantum states of light, and provide a means to deliver complex and compact quantum photonic circuits for applications in quantum communications, sensing and computation.

Integrated photonics offers great potential for quantum communication devices in terms of complexity, robustness, and scalability. Silicon photonics in particular is a leading platform for quantum photonic technologies, with further benefits of miniaturization, cost-effective device manufacture, and compatibility with CMOS microelectronics. However, effective techniques for high-speed modulation of quantum states in standard silicon photonic platforms have been limited. Here we overcome this limitation and demonstrate high-speed low-error quantum key distribution modulation with silicon photonic devices combining slow thermo-optic DC biases and fast (10 GHz bandwidth) carrier-depletion modulation. The ability to scale up these integrated circuits and incorporate microelectronics opens the way to new and advanced integrated quantum communication technologies and larger adoption of quantumsecured communications.

We demonstrate a fully integrated photonic transmitter for time-bin based multi-protocol quantum key distribution. This GHz rate Indium Phosphide device prepares states for Coherent One Way (COW), Differential Phase Shift (DPS), and BB84 protocols.

The homodyne detector is a primitive element in many quantum optics experiments. It is primarily a characterization device, used for measuring the quantum state of the electromagnetic field[1]. Quantum integrated photonics[2], in which optical sources, circuits, and detectors are monolithically integrated on a semi-conductor chip, provides a compact, scalable, platform in which to implement quantum devices like the homodyne detector.

We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability. We have begun to address the challenges of scaling up quantum circuits using new insights into how controlled operations can be efficiently realised, and demonstrated Shor's algorithm with consecutive CNOT gates and the iterative phase estimation algorithm. We have shown how quantum circuits can be reconfigured, using thermo-optic phase shifters to realise a highly reconfigurable quantum circuit able to perform almost any function on two photonic qubits, and electro-optic phase shifters in lithium niobate to rapidly manipulate the path and polarisation of telecomm wavelength single photons. We have addressed miniaturisation using multimode interference coupler architectures to directly implement NxN Hadamard operations and the `Boson sampling problem', and by using high refractive index contrast materials such as SiOxNy, in which we have implemented quantum walks of correlated photons, and Si, in which we have demonstrated generation of orbital angular momentum states of light. We have incorporated microfluidic channels for the delivery of samples to measure the concentration of a blood protein with entangled states of light. We have begun to address the integration of superconducting single photon detectors and diamond and non-linear single photon sources. Finally, we give an overview of recent work on fundamental aspects of quantum measurement, including a quantum version of Wheeler's delayed choice experiment.