Deterministic quantum teleportation of atomic qubits

Quantum teleportation provides a means to transport quantum information efficiently from one location to another, without the physical transfer of the associated quantum-information carrier. This is achieved by using the non-local correlations of previously distributed, entangled quantum bits (qubits). Teleportation is expected to play an integral role in quantum communication and quantum computation. Previous experimental demonstrations have been implemented with optical systems that used both discrete and continuous variables, and with liquid-state nuclear magnetic resonance. Here we report unconditional teleportation of massive particle qubits using atomic (9Be+) ions confined in a segmented ion trap, which aids individual qubit addressing. We achieve an average fidelity of 78 per cent, which exceeds the fidelity of any protocol that does not use entanglement. This demonstration is also important because it incorporates most of the techniques necessary for scalable quantum information processing in an ion-trap system.     

量子隐形传态的研究进展

量子隐形传态是量子信息理论的重要组成部分,也是量子计算的基础.文章中简单介绍了量子隐形传态的基本原理、理论和实验方案以及现阶段研究的最新进展,并且提出了进一步研究所需要解决的重要课题.     

连续变量的量子态受控超空间传送

提出一种除发送者与接收者之外还有第三者参与的连续变量量子态超空间传送的方案。在这个方案中,第三者是作为控制者出现的。由此,可能得到一个连续变量量子态超空间传送的网络,网络中的任意一个使用者均可向其他使用者传送量子态。     

一种可控量子隐形传态身份认证的方案

提出了一种实现可控量子隐形传态身份认证的方案.可信第三方Charlie利用纠缠交换原理对接收者Bob进行身份认证,在确定Bob的合法身份并将消息反馈给发送者Alice后,Alice再对量子信息进行传送.本方案能有效解决假冒身份攻击,从而保证量子信息传送的安全性.     

EPR粒子对与量子隐形传态

量子隐形传态,由发送者Alice将准备传送的信息分离成一部分纯粹经典的信息和另外一部分纯粹非经典的信息,通过2条不同的信道传送给接收者Bob。首先传送非经典部分,这需要借助于EPR粒子对,考虑由2个自旋皆为12的费密子构成,其中一个分配给Alice,另一个分配给Bob。Alice选择对她一方的原始粒子和她的EPR粒子一并进行冯.罗曼类型的测量,这个在贝尔算符的4个本征态中的测量,导致系统的波函数的波包坍缩为相互关联的4个贝尔基矢。Bob通过对他的EPR粒子的状态进行适当的幺正变换,能够重新构造出在Alice一方被＂毁灭＂了的原始粒子的状态。此外,这个贝尔测量产生2个比特的经典信息,传送给Bob,从而完成一个量子隐形传态。文章中研究了EPR粒子对与量子隐形传态的内在联系。     

Communications: quantum teleportation across the Danube

Efficient long-distance quantum teleportation is crucial for quantum communication and quantum networking schemes. Here we describe the high-fidelity teleportation of photons over a distance of 600 metres across the River Danube in Vienna, with the optimal efficiency that can be achieved using linear optics. Our result is a step towards the implementation of a quantum repeater, which will enable pure entanglement to be shared between distant parties in a public environment and eventually on a worldwide scale.     

Digital Multi-Signature Based on the Controlled Quantum Teleportation

In this paper, a scheme which can be used in multi-user quantum digital signature is proposed. The scheme of signature and verification is based on the characters of GHZ （Greenberger-Horne-Zeilinger） states and controlled quantum teleportation. Different from the digital signatures based on computational complexity, this scheme is unconditional secure, and compared to the former presented quantum signature scheme, it does not rely on an arbitrator to verify the signature and realize a message can be signed by multi-user together.     

Demonstration of a quantum teleportation network for continuous variables

Quantum teleportation involves the transportation of an unknown quantum state from one location to another, without physical transfer of the information carrier. Although quantum teleportation is a naturally bipartite process, it can be extended to a multipartite protocol known as a quantum teleportation network. In such a network, entanglement is shared between three or more parties. For the case of three parties (a tripartite network), teleportation of a quantum state can occur between any pair, but only with the assistance of the third party. Multipartite quantum protocols are expected to form fundamental components for larger-scale quantum communication and computation. Here we report the experimental realization of a tripartite quantum teleportation network for quantum states of continuous variables (electromagnetic field modes). We demonstrate teleportation of a coherent state between three different pairs in the network, unambiguously demonstrating its tripartite character.     

自由空间量子隐形传态实验中远程光符合的电子学系统研制

在两光子自由空间量子隐形传态实验方案中,设计了一套远程光符合的电子学系统,系统最小符合时间窗口约2ns.整个系统包括编码、解码、延时、高压驱动、符合、计数等模块.此系统实现了将实验中的经典信息和量子信息耦合在一起并通过自由空间传送到另一端进行在线符合来判定纠缠光子对.系统中编码模块将Alice端Bell基测量结果的时间标记信息和通道信息叠加在一起,通道信息的编码使用了奇偶校验和汉明码来降低事例丢失率和出错率,解码模块则分离出经典的时间标记信息和通道信息并做相应操作.完成了800m距离的两光子自由空间量子隐形传态实验,实验结果表明用本系统进行远程的实验是可行的.     

Cold atoms and quantum control

This overview prefaces a collection of Insight review articles on the physics and applications of laser-cooled atoms. I will cast this work into a historical perspective in which laser cooling and trapping is seen as one of several research directions aimed at controlling the internal and external degrees of freedom of atoms and molecules.     

四原子一般W态的确定隐形传态方案

提出一个基于QED腔技术的四原子一般W态的确定隐形传态方案.方案将联合贝尔态测量转化为两个单原子态的测量,从而实现四原子一般W态的确定隐形传态,该方案成功的概率可以达到1,并且不受腔衰减和热场的影响.     

利用部分纠缠的量子信道确定性地实现N→1和1→N的受控量子远程旋转

提出利用部分纠缠的量子信道确定性地实现多个发送者1个接受者和1个发送者多个接受者的受控量子远程旋转方案.首先考虑利用两个(N?M?1)粒子部分纠缠的Greenberger-Horne-Zeilinger(GHZ)态确定性地实现N个发送者在M个监控者的控制下确定性地将她们的旋转分别传给远处接受者的操作(N→1).然后考虑在一个(2K?M?1)粒子部分纠缠的Einstein-Podolsky-Rosen(EPR)-GHZ态或K个(M+2)粒子部分纠缠的GHZ态辅助下,发送者随意地将她的旋转分为N份(NK)并在M个监控者的控制下确定性地将它们分别传给远处N个接受者的操作(1→N).方案中,量子旋转的发送者或接受者或监控者的正定算符值测量(POVM)起着关键作用,我们给出了它们的数学表式.值得注意的是,用非理想的量子信道可确定性地实现N→1或1→N的量子远程旋转.这些方案可用于量子秘密共享,量子选举等,它们具极强的保密性.     

量子隐形传态中纠缠态制备的研究进展

量子隐形传态是量子力学和信息科学等形成的交叉课题,同时也是近些年来人们研究的热点之一。文章首先回顾了Bennett等人所提出的量子隐形传态的基本思想和基本原理,然后着重介绍了量子隐形传态中的重要步骤,即量子纠缠态的制备及其在传统上和近年来的一些具有代表性的实验实现方案。     

利用腔-QED进行两原子任意态量子隐态传输方案

基于腔QED技术,我们提出一种无需Bell态联合测量的两原子任意态量子隐态传输方案．在传输过种中,在一个强经典场驱动下,原子与非共振的单模腔场相互作用,对原子的分离测量来代替实验上难以实现的联合Bell态测量,且不受腔泄漏及环境热库的影响,     

Resonant quantum transitions in trapped antihydrogen atoms

The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.     

Deterministic secure quantum communication and authentication protocol based on three-particle W state and quantum one-time pad

Three-particle W states are used as decoy photons, and the eavesdropping detection rate reaches 63 %. The positions of decoy photons in information sequence are encoded with identity string ID of the legitimate users. Authentication is implemented by using previously shared identity string. State 丨φ^- ） is used as the carrier. One photon of 丨φ^-） is sent to Bob; and Bob obtains a random key by measuring photons with bases dominated by ID. The bases information is secret to others except Alice and Bob. Both the eavesdropping detection based on three-particle W state and the secret ID ensure the security of the protocol. Unitary operations are not used.     

Single atoms in the ring lattice for quantum information processing and quantum simulation

We have demonstrated preparing and rotating single neutral rubidium atoms in an optical ring lattice generated by a spatial light modulator, inserting two atoms into a single microscopic optical potential efficiently by dynamically reshaping the optical dipole trap, trapping single atoms in a blue detuned optical bottle beam trap, and confining single atoms into the Lamb-Dicke regime by combining red and blue detuned optical potentials. In combination with the manipulation of internal states of single atoms, the study is opening a way for research in the field of quantum information processing and quantum simulation. In this paper we review the past works and discuss the prospects.     

An elementary quantum network of single atoms in optical cavities

Quantum networks are distributed quantum many-body systems with tailored topology and controlled information exchange. They are the backbone of distributed quantum computing architectures and quantum communication. Here we present a prototype of such a quantum network based on single atoms embedded in optical cavities. We show that atom-cavity systems form universal nodes capable of sending, receiving, storing and releasing photonic quantum information. Quantum connectivity between nodes is achieved in the conceptually most fundamental way-by the coherent exchange of a single photon. We demonstrate the faithful transfer of an atomic quantum state and the creation of entanglement between two identical nodes in separate laboratories. The non-local state that is created is manipulated by local quantum bit (qubit) rotation. This efficient cavity-based approach to quantum networking is particularly promising because it offers a clear perspective for scalability, thus paving the way towards large-scale quantum networks and their applications.