Some years ago quantum hacking became popular: devices implementing the unbreakable quantum cryptography were shown to have imperfections which could be exploited by attackers. Security has been thoroughly enhanced, as a consequence of both theoretical and experimental advances. This review gives both sides of the story, with the current best theory of quantum security, and an extensive survey of what makes quantum cryptosystem safe in practice.

Secure quantum key distribution with realistic devices

In mathematics and computer science, random numbers have the role of a resource for assisting proofs, making cryptography secure, and enabling computational protocols. This role motivates efforts to produce random numbers as a physical process. Potential physical sources abound, but arguably the most fundamental are those based on elementary quantum mechanical processes. This review discusses the current status of devices that generate quantum random numbers.

Quantum random number generators

During the past few years, metasurfaces have been used to demonstrate optical elements and systems with capabilities that surpass those of conventional diffractive optics. Here, we review some of these recent developments, with a focus on dielectric structures for shaping optical wavefronts. We discuss the mechanisms for achieving steep phase gradients with high efficiency, simultaneous polarization and phase control, controlling the chromatic dispersion, and controlling the angular response. Then, we review applications in imaging, conformal optics, tunable devices, and optical systems. We conclude with an outlook on future potentials and challenges that need to be overcome.

https://www.degruyter.com/document/doi/10.1515/nanoph-2017-0129/pdf

A review of dielectric optical metasurfaces for wavefront control

2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

Abstract The emergence of silicon photonics over the past two decades has established silicon as a preferred substrate platform for photonic integration. While most silicon-based photonic components have so far been realized in the near-infrared (near-IR) telecommunication bands, the mid-infrared (mid-IR, 2–20-μm wavelength) band presents a significant growth opportunity for integrated photonics. In this review, we offer our perspective on the burgeoning field of mid-IR integrated photonics on silicon. A comprehensive survey on the state-of-the-art of key photonic devices such as waveguides, light sources, modulators, and detectors is presented. Furthermore, on-chip spectroscopic chemical sensing is quantitatively analyzed as an example of mid-IR photonic system integration based on these basic building blocks, and the constituent component choices are discussed and contrasted in the context of system performance and integration technologies.

/pdf/mid-infrared-integrated-photonics-on-silicon-a-perspective-31psns51w2.pdf

Mid-infrared integrated photonics on silicon: a perspective

We present a high-quality bias-free quantum random number generator (QRNG) using photon arrival time selectively, in accordance with the number of photon detection events within a sampling time interval in attenuated light. It is well shown in both theoretical analysis and experimental verification that this random number production method eliminates both bias and correlation perfectly without more postprocessing and that the random number can clearly pass the standard randomness tests. We fulfill theoretical analysis and experimental verification of the method whose rate can reach up to 45 Mb/s.

A Bias-Free Quantum Random Number Generation Using Photon Arrival Time Selectively

We present a practical high-speed quantum random number generator, where the timing of single-photon detection relative to an external time reference is measured as the raw data. The bias of the raw data can be substantially reduced compared with the previous realizations. The raw random bit rate of our generator can reach 109 Mbps. We develop a model for the generator and evaluate the min-entropy of the raw data. Toeplitz matrix hashing is applied for randomness extraction, after which the final random bits are able to pass the standard randomness tests.

Practical and fast quantum random number generation based on photon arrival time relative to external reference

A real-time quantum key distribution (QKD) system is developed in this paper. In the system, based on the feature of a field-programmable gate array, secure key extraction control and algorithm have been optimally designed to perform sifting, error correction, and privacy amplification altogether in real time. In the QKD experiment, information synchronization mechanism and high-speed classic data channel are designed to ensure the steady operation of the system. Decoy state and synchronous laser light source are used in the system, while the length of optical fiber between Alice and Bob is 20 km. With photons repetition frequency of 20 MHz, the final key rate could reach 17 kb/s. Smooth and robust operation is verified with 6 h continuous test and associated with encrypted voice communication test.

A Real-Time QKD System Based on FPGA

Quantum physics allows for unconditionally secure communication between parties that trust each other. However, when the parties do not trust each other such as in the bit commitment scenario, quantum physics is not enough to guarantee security unless extra assumptions are made. Unconditionally secure bit commitment only becomes feasible when quantum physics is combined with relativistic causality constraints. Here we experimentally implement a quantum bit commitment protocol with relativistic constraints that offers unconditional security. The commitment is made through quantum measurements in two quantum key distribution systems in which the results are transmitted via free-space optical communication to two agents separated with more than 20 km. The security of the protocol relies on the properties of quantum information and relativity theory. In each run of the experiment, a bit is successfully committed with less than $5.68\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}2}$ cheating probability. This demonstrates the experimental feasibility of quantum communication with relativistic constraints.

Hong-fei Zhang

Papers

A Bias-Free Quantum Random Number Generation Using Photon Arrival Time Selectively

Practical and fast quantum random number generation based on photon arrival time relative to external reference

Practical and fast quantum random number generation based on photon arrival time relative to external reference

A Real-Time QKD System Based on FPGA

Experimental Unconditionally Secure Bit Commitment