Ultra‐fast heralded single photon source based on telecom technology

The realization of an ultra‐fast source of heralded single photons emitted at the wavelength of 1540 nm is reported. The presented strategy is based on state‐of‐the‐art telecom technology, combined with off‐the‐shelf fiber components and waveguide non‐linear stages pumped by a 10 GHz repetition rate laser. The single photons are heralded at a rate as high as 2.1 MHz with a heralding efficiency of 42%. Single‐photon character of the source is inferred by measuring the second‐order autocorrelation function. For the highest heralding rate, a value as low as 0.023 is found. This not only proves negligible multi‐photon contributions but also represents one of the best measured values reported to date for heralding rates in the MHz regime. These performances, associated with a device‐like configuration, are key ingredients for both fast and secure quantum communication protocols.

     

Active demultiplexing of single photons from a solid‐state source

A scheme for active temporal‐to‐spatial demultiplexing of single photons generated by a solid‐state source is introduced. The scheme scales quasi‐polynomially with photon number, providing a viable technological path for routing n photons in the one temporal stream from a single emitter to n different spatial modes. Active demultiplexing is demonstrated using a state‐of‐the‐art photon source—a quantum‐dot deterministically coupled to a micropillar cavity—and a custom‐built demultiplexer—a network of electro‐optically reconfigurable waveguides monolithically integrated in a lithium niobate chip. The measured demultiplexer performance can enable a six‐photon rate three orders of magnitude higher than the equivalent heralded SPDC source, providing a platform for intermediate quantum computation protocols.

     

基于标记配对相干态光源的诱骗态量子密钥分配性能分析

从有效性、稳定性和可行性三个方面, 对基于标记配对相干态光源的诱骗态量子密钥分配的性能进行了全面分析. 采用四组实验数据对基于标记配对相干态光源的三强度诱骗态方案的密钥生成效率、量子比特误码率和最优信号态强度与安全传输距离之间的关系进行了仿真和分析; 考虑到光源涨落, 对方案的稳定性进行了讨论和仿真; 并对基于标记配对相干态光源设计简单易实现方案的可行性进行了分析. 结论表明: 基于标记配对相干态光源的诱骗态方案性能在安全传输距离和密钥生成效率两方面都优于现有基于弱相干态光源和预报单光子源的诱骗态方案; 在光源强度涨落相同条件下, 标记配对相干态光源的稳定性逊于预报单光子源, 而优于相干态光源. 但是标记配对相干态光源在有效性上的优势可弥补其在稳定性上的不足; 且标记配对相干态光源的双模特性为设计简单易实现的被动诱骗态方案提供了条件. 关键词： 量子光学 量子密钥分配 标记配对相干态光源 性能     

利用诱骗信号方案进行实用的量子密钥分发

真实量子密钥分发系统中不完善的单光子源和信道损耗的存在,使得现有基于弱相干态的量子密码实验在分束攻击下并不安全,诱骗信号方案能实现基于现有技术绝对安全的量子密钥分发,并能有效提高密钥分发率和安全传输距离,因此成为近年来量子通信研究的热点问题.结合现实量子密码系统的一般模型,介绍目前几种典型的诱骗信号方案以及实验进展,综述了诱骗信号方案的发展情况和最新成果,并对未来的研究方向进行了展望.     

Atomic spectroscopy and quantum optics in hollow‐core waveguides

Atomic spectroscopy is a well‐established, integral part of the physicist's toolbox with an extremely broad range of applications ranging from astronomy to single atom quantum optics. While highly desirable, miniaturization of atomic spectroscopy techniques on the chip scale was hampered by the apparent incompatibility of conventional solid‐state integrated optics and gaseous media. Here, the state of the art of atomic spectroscopy in hollow‐core optical waveguides is reviewed The two main approaches to confining light in low index atomic vapors are described: hollow‐core photonic crystal fiber (HC‐PCF) and planar antiresonant reflecting optical waveguides (ARROWs). Waveguide design, fabrication, and characterization are reviewed along with the current performance as compact atomic spectroscopy devices. The article specifically focuses on the realization of quantum interference effects in alkali atoms which may enable radically new optical devices based on low‐level nonlinear interactions on the single photon level for frequency standards and quantum communication systems.     

Flying qubits and entangled photons

Efficient generation of polarized single photons or entangled photon pairs is crucial for the implementation of quantum key distribution (QKD) systems. Self organized semiconductor quantum dots (QDs) are capable of emitting on demand one polarized photon or an entangled photon pair upon current injection. Highly efficient single‐photon sources consist of a pin structure inserted into a microcavity where single electrons and holes are funneled into an InAs QD via a submicron AlOx aperture, leading to emission of single polarized photons with record purity of the spectrum and non‐classicality of the photons. A new QD site‐control technique is based on using the surface strain field of an AlO_x current aperture below the QD. GaN/AlN QD based devices are promising to operate at room temperature and reveal a fine‐structure splitting (FSS) depending inversely on the QD size. Large GaN/AlN QDs show disappearance of the FSS. Theory also suggests QDs grown on (111)‐oriented GaAs substrates as source of entangled photon pairs.     

Heralded linear optical quantum Fredkin gate based on one auxiliary qubit and one single photon detector

Linear optical quantum Fredkin gate can be applied to quantum computing and quantum multi-user communication networks. In the existing linear optical scheme, two single photon detectors （SPDs） are used to herald the success of the quantum Fredkin gate while they have no photon count. But analysis results show that for non-perfect SPD, the lower the detector efficiency, the higher the heralded success rate by this scheme is. We propose an improved linear optical quantum Fredkin gate by designing a new heralding scheme with an auxiliary qubit and only one SPD, in which the higher the detection efficiency of the heralding detector, the higher the success rate of the gate is. The new heralding scheme can also work efficiently under a non-ideal single photon source. Based on this quantum Fredkin gate, large-scale quantum switching networks can be built. As an example, a quantum Bene~ network is shown in which only one SPD is used.     

High‐resolution spectral characterization of two photon states via classical measurements

Quantum optics plays a central role in the study of fundamental concepts in quantum mechanics, and in the development of new technological applications. Typical experiments employ sources of photon pairs generated by parametric processes such as spontaneous parametric down‐conversion and spontaneous four‐wave‐mixing. The standard characterization of these sources relies on detecting the pairs themselves and thus requires single photon detectors, which limit both measurement speed and accuracy. Here it is shown that the two‐photon quantum state that would be generated by parametric fluorescence can be characterised with unprecedented spectral resolution by performing a classical experiment. This streamlined technique gives access to hitherto unexplored features of two‐photon states and has the potential to speed up design and testing of massively parallel integrated nonlinear sources by providing a fast and reliable quality control procedure. Additionally, it allows for the engineering of quantum light states at a significantly higher level of spectral detail, powering future quantum optical applications based on time‐energy photon correlations.     

Generation of quantum‐entangled twin photons by waveguide nonlinear‐optic devices

This paper reviews the quasi‐phase‐matched (QPM) waveguide nonlinear‐optic device technologies for generation of quantum‐entangled twin photons indispensable for quantum‐information techniques. After a brief introduction to the concept of entanglement, quantum theory analysis of twin‐photon generation (TPG) is outlined to clarify the properties of twin photons. Then, methods for entangled‐photon generation are discussed. Practical design and theoretical performances of LiNbO₃ waveguide QPM TPG devices, as well as the fabrication techniques, are described. Finally, experimental demonstrations of polarization‐entangled twin‐photon generation by waveguide Type‐I and Type‐II QPM TPG devices are presented.     

Experimental realization of quantum cryptography communication in free space

Quantum cryptography is a new secure communication protocol with the combina- tion of quantum mechanics and information theory[1]. Its security depends on the laws of physics and has been proved strictly[2,3]. Quantum communication is the art of generat- ing and transmitting the keys through a quantum channel between two parties, usually called Alice and Bob. Unlike the classical key distribution, the quantum keys are gener- ated in the process of transmission instantaneously. The keys can be…     

Isolated single quantum dot emitters in all-epitaxial microcavities

Data are presented on a fabrication approach that places an isolated single quantum dot at the center of a semiconductor microcavity. The microcavity is based on an all-epitaxial mesa-confined design that is mechanically robust and provides the thermal dissipation needed for a single photon source device technology. Microphotoluminescence is used to reveal single quantum dot emission with the essential optical properties of single quantum emitters.     

On‐chip single photon sources using planar photonic crystals and single quantum dots

We review the basic light‐matter interactions and optical properties of chip‐based single photon sources, that are enabled by integrating single quantum dots with planar photonic crystals. A theoretical framework is presented that allows one to connect to a wide range of quantum light propagation effects in a physically intuitive and straightforward way. We focus on the important mechanisms of enhanced spontaneous emission, and efficient photon extraction, using all‐integrated photonic crystal components including waveguides, cavities, quantum dots and output couplers. The limitations, challenges, and exciting prospects of developing on‐chip quantum light sources using integrated photonic crystal structures are discussed.     

Single photon sources with single semiconductor quantum dots

In t.his contribution, we briefly recall the basic concepts of quantum optics and properties of semicon- ductor quantum clot. （QD） which a.re necessary to the nnderstanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantmn emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as opti- cal properties of the QDs. We then review the localizatioll of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and perfornances in terms of strong coupling regime, elfieiency, directionality, and polarization control. Furthermore, we will discuss the recenl, progress on the fabrication of single photon sources, and various a.pproaehes for embedding single QDs into mieroca,vities or photonic crystal nanoeavities and show how to ex- tend the wavelength range. We focus in part;icular on new generations of electrically driven QD single photon source leading to high repetition rates, efficiencies at elevated temperature operation. Besides strong eoupling regime, and high collection new development;s of room temperature sin- gle photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for pract ical single-photon sources are also discussed.     

Towards High-Dimensional Entanglement in Path: Photon-Source Produced from a Two-Dimensional Atomic Cloud

A photon source with high-dimensional entanglement is able to bring increasing capacity of information in quantum communication.The dimensionality is determined by the chosen degree of freedom of the photons and is limited by the complexity of the physical systems.Here we propose a new type of high-dimensional entangled photon source,generated via path-indistinguishable scheme from a two-dimensional atomic cloud,which is prepared in a magneto-optical trap.To verify the photon source,we demonstrate experimentally the quantum state of the single photons heralded by its partner photon,with homodyne tomographic technology.     

Deterministic separation of arbitrary photon pair states in integrated quantum circuits

Entangled photon pairs must often be spatially separated for their subsequent manipulation in integrated quantum circuits. Separation that is both deterministic and universal can in principle be achieved through anti‐coalescent two‐photon quantum interference. However, such interference‐facilitated pair separation (IFPS) has not been extensively studied in the integrated setting, which has important implications on performance. This work provides a detailed review of IFPS and examines how integrated device dependencies such as dispersion impact separation fidelity and interference visibility. The analysis applies equally to both on‐chip and in‐fiber implementations. When coupler dispersion is present, the separation performance can depend on photon bandwidth, spectral entanglement and the dispersion. By design, reduction in the separation fidelity due to loss of non‐classical interference can be perfectly compensated for by classical wavelength demultiplexing effects. This work informs the design of devices for universal photon pair separation of states with tunable arbitrary properties.

     

基于光子统计测量的单分子判别

基于标准的Hanbury-Brown-Twiss探测方式下，研究了具有Poisson统计背景的实际单分子光子源与理想双分子系统的光子统计特性，通过比较分析二者在具有相同平均光子数n—时的Mandel参数，研究给出一种利用双光子的统计概率P(2)判别单分子的方法为P(2)<12(2-4-2n—)².同时研究了单分子光子源的信号/背景比对分析结果的影响. 关键词： 单分子 Mandel参数 Poisson分布 信号/背景比     

单分子光子源光子统计的非平衡探测

研究了在Hanbury Brown Twiss探测方式下，非平衡探测系统对光子统计测量的影响。通过记录2个单光子计数器响应的单分子光子源输出的每一个事件，分析具有泊松统计背景的实际单分子光子源的光子统计特性，讨论并给出了非平衡探测系统的单分子光子源Mandel参数。研究表明：非理想的50／50分束器、非理想的线性传输效率和非理想的探测器都会使单分子光子源Mandel参数的实际测量结果小于平衡系统的Mandel参数，最后给出了单分子光子源Mandel参数的非理想探测的校正表达式。     

Reinterpretation of two-photon interference experiment using advanced field

The recent two-photon interference experiments by Wang, Zou, and Mandel, with and without a time-dependent light switch introduced into one of interferometer arms, indicate the collapse of photon waves along empty arms, not travelled by the detected photon, at a critical moment on the light cone backwards from the detected photon. It is proposed to interpret the Schrödinger's retarded wave equation as an operator acting on the advanced field satisfying the final condition of the experiment. In this time-symmetrical formulation the advanced field of the detected particle guides the retarded wave from the particle source not to enter empty arms, and the critical moment is interpreted as the time of the passage of the advanced field through the light switch. By changing the relative optical lengths of interferometer arms and observing the independence of the result of the experiment on the relative position of the detectors, we could conceive of the unarousal of the empty wave destined to collapse.     

Optimized IR synchrotron beamline design

Synchrotron infrared beamlines are powerful tools on which to perform spectroscopy on microscopic length scales but require working with large bending‐magnet source apertures in order to provide intense photon beams to the experiments. Many infrared beamlines use a single toroidal‐shaped mirror to focus the source emission which generates, for large apertures, beams with significant geometrical aberrations resulting from the shape of the source and the beamline optics. In this paper, an optical layout optimized for synchrotron infrared beamlines, that removes almost totally the geometrical aberrations of the source, is presented and analyzed. This layout is already operational on the IR beamline of the Brazilian synchrotron. An infrared beamline design based on a SOLEIL bending‐magnet source is given as an example, which could be useful for future IR beamline improvements at this facility.     

Probabilistic and robust preparation of a GHZ-type state via atomic ensembles and linear optics

This paper proposes two simple and robust schemes to generate an atomic-ensemble Greenberger--Horne--Zeilinger-type (GHZ-type) entangled state via linear optics and single photon detection. These schemes are based on two-photon Hong--Ou--Mandel-type interference, therefore they are insensitive to the phase fluctuation. This advantage will make the realizations of these two schemes easier. One scheme can scale efficiently with the number of ensembles because of the used quantum memory. Both schemes are also robust to the noise and within the reach of current technology.