单光子偏振态实现量子密钥分配的方案

提出一个基于单光子偏振的量子密钥分配方案.在这个方案里, Alice首先制备一串任意单光子态,然后发送给Bob.Bob只需对其进行一个U操作,再发回Alice.最后Alice对单光子态进行测量,即可实现量子密钥分配.此方案需要一个无噪声信道,优点在于仅仅需要单光子态,以及局域操作和单光子偏振态的测量,这些都非常易于实现.最后其安全性也是有理论保证的.     

Strain tunable quantum dot based non-classical photon sources

Semiconductor quantum dots are leading candidates for the on-demand generation of single photons and entangled photon pairs.High photon quality and indistinguishability of photons from different sources are critical for quantum information applications.The inability to grow perfectly identical quantum dots with ideal optical properties necessitates the application of post-growth tuning techniques via e.g.temperature,electric,magnetic or strain fields.In this review,we summarize the state-of-the-art and highlight the advantages of strain tunable non-classical photon sources based on epitaxial quantum dots.Using piezoelectric crystals like PMN-PT,the wavelength of single photons and entangled photon pairs emitted by InGaAs/GaAs quantum dots can be tuned reversibly.Combining with quantum light-emitting diodes simultaneously allows for electrical triggering and the tuning of wavelength or exciton fine structure.Emission from light hole exciton can be tuned,and quantum dot containing nanostructure such as nanowires have been piezo-integrated.To ensure the indistinguishability of photons from distant emitters,the wavelength drift caused by piezo creep can be compensated by frequency feedback,which is verified by two-photon interference with photons from two stabilized sources.Therefore,strain tuning proves to be a flexible and reliable tool for the development of scalable quantum dots-based non-classical photon sources.     

Quantum light source devices of In(Ga)As semiconductor self-assembled quantum dots

A brief introduction of semiconductor self-assembled quantum dots (QDs) applied in single-photon sources is given. Single QDs in confined quantum optical microcavity systems are reviewed along with their optical properties and coupling characteristics. Subsequently, the recent progresses in In(Ga)As QDs systems are summarized including the preparation of quantum light sources, multiple methods for embedding single QDs into different microcavities and the scalability of single-photon emitting wavelength. Particularly, several In(Ga)As QD single-photon devices are surveyed including In(Ga)As QDs coupling with nanowires, InAs QDs coupling with distributed Bragg reflection microcavity and the In(Ga)As QDs coupling with micropillar microcavities. Furthermore, applications in the field of single QDs technology are illustrated, such as the entangled photon emission by spontaneous parametric down conversion, the single-photon quantum storage, the chip preparation of single-photon sources as well as the single-photon resonance-fluorescence measurements.     

非相干变频转换实现室温下红外单光子源

纳米金刚石中的NV-center(Nitrogen-Vacancy center)是目前室温下具有高发射率和稳定性的可见光波段单光子源,而如何实现及优化红外单光子源则是未来实现量子信息和量子通信应用的一大挑战.介绍了一种近期提出的实现红外单光子源的新型机制.该方法以金刚石中的NV-center作为可见光波段的单光子源,利用非相干变频转换实现室温下近红外波段稳定、无闪烁的单光子源.具体的实施方案为在中空芯光子晶体光纤中选择性地填充含有量子点的溶液,以可见光波段的单光子源作为激励源,选择合适的量子点即可得到红外波段的单光子源.中空芯光子晶体光纤保证了较高的单光子吸收效率以及荧光收集效率.该方案的实施在理论上可以达到26%的转换效率,而初步的实验得到了0.1%的转换效率.进一步分析了一些影响转换效率的因素,并提出了一些解决方案.     

Quantum-Dot Sources for Single Photons and Entangled Photon Pairs

Quantum dots show excellent promise as triggered sources of both single and polarization entangled photons for quantum information applications. Our recent progress developing nonclassical light sources with single quantum dots is presented in this paper. Following radiative emission of an exciton confined in a quantum dot, there is a finite delay before re-excitation can occur; this results in an anti-bunching of the photons emitted providing a source of single photons. Excitation of a quantum dot with two electrons and two holes leads to the emission of a pair of photons; we show here that, provided the spin splitting of the intermediate exciton state in the decay is erased, the photon pair is emitted in an entangled polarization state. The fidelity of this entangled state is shown to exceed 70%. Using quantum dots to generate quantum light allows contacts for electrical injection to be integrated into a compact and robust device. A cavity may also be integrated into the semiconductor structure to enhance the photon collection efficiency and control the recombination dynamics. We detail a process to form a submicrometer current aperture within an electrical device, allowing individual quantum dots to be addressed electrically in devices.     

Element base of quantum informatics II: Quantum communications with single photons

Quantum cryptography can provide almost complete security of the data transmitted in optical telecommunication systems by single photons based on the laws of quantum mechanics. The paper presents a brief overview of the element base and experimental investigations in the field of quantum cryptography and data transmission by single photons in atmospheric and optical fiber quantum communication lines. Two experimental setups for the single-photon quantum key distribution in the atmospheric and optical fiber quantum channels are described. The results of the quantum key distribution experiments performed on them are given.     

高非线性光纤中光子对产生中的噪声及其抑制

在高非线性光纤中产生高质量的光子对对于量子信息的应用具有重要意义.在分析基于光纤中四波混频效应产生光子对原理的基础上,指出了影响光子对产生噪声的主要因素.讨论了抑制噪声的几种可能的方法,采用冷却光纤、短脉冲泵浦光源和狭窄的滤波宽度和增大四波混频的信号和闲频光带宽等方法可以有效地降低噪声,从而为高效产生光子对提供了依据.     

单光子探测器研究现状与发展

单光子探测器的研制是量子光学和量子信息领域的一个重要研究课题。单光子探测器突破了传统探测器只针对振幅进行采样的局限,同时对光波或者光子的偏振、波矢、位相等特性进行探测,具有可保持测量信号完整性、理论量子效率高、工作电压低、探测灵敏度高等优点,同时具有室温单光子探测的潜力。为了深入了解单光子探测器的研究现状和发展前景,本文介绍了单光子探测器的工作机理,总结对比了光电倍增管、雪崩光电二极管等传统单光子探测器以及基于新型二维材料的雪崩光电二极管、超导纳米线单光子探测器等新型单光子光电探测器的优势与不足,并对其发展前景进行了展望。此外还介绍了单光子探测器在量子通信、激光测距和成像等领域的应用。     

Impact of Fiber Dispersion on Performance of Entanglement-Based Dispersive Optics Quantum Key Distribution

Dispersive optics quantum key distribution (DO-QKD) based on energy-time entangled photon pairs is an important QKD scheme. In DO-QKD, the arrival time of photons is used in key generation and security analysis, which would be greatly affected by fiber dispersion. In this work, we establish a theoretical model of the entanglement-based DO-QKD system, considering the protocol, physical processes (such as fiber transmission and single-photon detection), and the analysis of security tests. Based on this theoretical model, we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD. By analyzing the benefits and costs of dispersion compensation, the system performance under G.652 and G.655 optical fibers are shown, respectively. The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks. Whereas, it is still required in DO-QKD systems with longer fiber transmission distances.     

空间量子通信技术

利用卫星来分发单光子（或纠缠光子对）的方法为远程量子通信网络提供了一种独特的解决方案。这将克服现有的光纤和陆上自由空间链路所带来的距离限制，实现真正意义上的全球量子通信。本文对这种设想进行了分析，证明这种设想有很高可行性。     

基于光电倍增管单光子脉冲幅度分布的多比特光量子随机源

提出并验证了一种基于光电倍增管单光子脉冲高 度分布的多比特光量子随机源。将紫外LED发出 的光衰减成离散的单光子序列,光电倍增管探测到的单光子后,输出脉冲幅度随机分布的单 光子脉冲,通 过数字化单光子脉冲的峰值作为熵源来提取随机数,实现了一个单光子事件产生多个随机比 特位。为减小 所提取原始随机数存在的偏差,提出并实现了基于FPGA的SHA-256后 处理方法。光量子随机源工作在 500kc/s时,平均每个探测光子可提取7bit随机位,获得了3.5Mbit/s的随机位产生速率。运用随机性 测试程序ENT和STS对所获的随机位序列进行测试,测试结果表明,序列的随机性满足真随机 数的标准。     

Maximum-likelihood image estimation using photon-correlated beams

A theory is presented addressing the fundamental limits of image estimation in a setup that uses two photon-correlated beams. These beams have the property that their photon arrivals, as a point process, are ideally synchronized in time and space. The true image represents the spatial distribution of the optical transmittance (or reflectance) of an object. In this setup, one beam is used to probe the image while the other is used as a reference providing additional information on the actual number of photons impinging on the object. This additional information is exploited to reduce the effect of quantum noise associated with the uncertainty in the number of photons per pixel. A stochastic model for the joint statistics of the two observation matrices is developed and used to obtain a local maximum-likelihood estimator of the image. The model captures the nonideal nature of the correlation between the photons of the beams by means of a simple random translation model. The mean-square error of the estimator is evaluated and compared to the corresponding conventional techniques. Conditions for the performance advantage of the proposed estimator are examined in terms of key system parameters. The theoretical predictions are demonstrated by means of simulation.     

用于1 550 nm光子检测的InGaAs/InP 单光子雪崩二极管的温度相关性

在越来越多的光子计数应用中,用于近红外光波长领域的单光子探测器受到广泛关注。例如在量子信息处理、量子通信、3D激光测距（LiDAR）、时间分辨光谱等光子计数应用领域。文中设计并展示了用于探测1 550 nm波长光子的InGaAs/InP单光子雪崩二极管（SPAD）。这种SPAD 采用分离吸收、过渡、电荷和倍增区域结构 (SAGCM),在盖革模下工作时具有单光子灵敏度。SPAD的特性包括随温度范围223~293 K变化的击穿电压、暗计数率、单光子检测效率和后脉冲概率。25 μm 直径的 SPAD 显示出一定的温度相关性,击穿电压随温度的变化率约为100 mV/K。当SPAD在盖革模式下温度为223 K工作时,在暗计数率为4.1 kHz,后脉冲概率为3.29%的基础上,对1 550 nm光子实现了21%的单光子探测效率。文中还分析和讨论了SPAD温度相关性的单光子探测效率、暗计数率和后脉冲概率的来源和物理机制。这些机制分析、讨论和计算可以为SPAD的设计和制备提供更多的理论支持和依据。     

Stable single photon sources in the near C-band range above 400 K

The intrinsic characteristics of single photons became critical issues since the early development of quantum mechanics. Nowadays, acting as flying qubits, single photons are shown to play important roles in the quantum key distribution and quantum networks. Many different single photon sources (SPSs) have been developed. Point defects in silicon carbide (SiC) have been shown to be promising SPS candidates in the telecom range. In this work, we demonstrate a stable SPS in an epitaxial 3CSiC with the wavelength in the near C-band range, which is very suitable for fiber communications. The observed SPSs show high single photon purity and stable fluorescence at even above 400 K. The lifetimes of the SPSs are found to be almost linearly decreased with the increase of temperature. Since the epitaxial 3C-SiC can be conveniently nanofabricated, these stable near Cband SPSs would find important applications in the integrated photonic devices.     

A quantum multiple access communications scheme using orbital angular momentum

We propose a quantum multiple access communications scheme using Orbital Angular Momentum (OAM) sector states in the paper. In the scheme, each user has an individual modified Poincare Bloch sphere and encodes his information with his own corresponding sector OAM states. A prepared entangled photon pairs are separated at transmitter and receiver. At the transmitter, each user encodes his information with the sector OAM states on the photons and the superposition of the different sector OAM states is carried by the photons. Then the photons are transmitted through quantum noiseless channel to the receiver. At the receiver, each user could retrieve his information by coincidently measuring the transmitted photons with the receiver side photons which are modulated by a special prepared measurement basis. The theoretical analysis and the numerical simulations show that each user could get his information from the superposition state without error. It seems that this scheme provides a novel method for quantum multiple users communications.     

A single-photon counter for long-haul telecom

Quite a few groups have turned their attention to using commercially available InGaAs/InP APDs, originally developed for optical communication applications, as SPADs for photon counting at 1300 nm and 1550 nm. This research has turned out to be quite fruitful, and there are many applications emerging in optical metrology (optical time-domain reflectometry) in eye-safe range finding and in future quantum technologies, where databits are encoded on individual photons. This article describes the status of these commercially available InGaAs/InP APDs used as single-photon counters in the telecom wavelength region of 1550 nm     

单光子源和单光子探测器研究进展

在众多的量子信息方案中,光学方法是独特的,因为它们允许长距离的通信且提供量子计算新的方法.在光量子信息处理过程中,单光子源和探测器是很重要的一个方面.本文回顾了测量和产生单光子的方法,且讨论了它们在量子信息处理中的应用.     

利用单光子探测器测量多光子响应时间

通过研究单光子探测器对微弱激光脉冲的暂态响 应特性,利用不同光子数的响应时间实现光 子数的分辨测量。理论上分析了光子数响应时间与微弱光脉冲探测时间的对应关系。实验上 通过测量不同光强下单光子探测器的暂态响应,测量到1550nm波段单光子、 双光子和三光子的响应时间分别为10.73±0.17、8.75±0.32和5.98±0.77ns。实现精确区分微弱光场中的光子数。分析了单光子探测器光子数统计涨落引起的 微弱激光脉冲的探测时间变化对光子数响应时间测量的影响。     

Physical Modeling of Hot-Electron Superconducting Single-Photon Detectors

In this paper, we treat the incident photons as an electromagnetic plane wave and simulate the wave power coupling to the the hot-electron superconducting single-photon detector to investigate its connection with the experimental system quantum efficiency over different wavelengths. Then we propose a lumped equivalent circuit model based on the kinetic inductance variation induced by the incident photon stream when the serpentine superconducting thin-film nano-wire is dc-biased close to its critical current. The computed output voltage matches experimental results for both amplitude and frequency.