Quantum Parallelism in Quantum Information Processing

We investigate distinguishability (measured by fidelity) of the initial and the final state of a qubit, which is an object of the so-called nonideal quantum measurement of the first kind. We show that the fidelity of a nonideal measurement can be greater than the fidelity of the corresponding ideal measurement. This result is somewhat counterintuitive, and can be traced back to the quantum parallelism in quantum operations, in analogy with the quantum parallelism manifested in the quantum computing theory. In particular, as the quantum parallelism in quantum computing underlies efficient quantum algorithms, the quantum parallelism in quantum information theory underlies the classically unexpected increase of fidelity.     

Quantum Secure Dialogue with Quantum Encryption

How to solve the information leakage problem has become the research focus of quantum dialogue. In this paper, in order to overcome the information leakage problem in quantum dialogue, a novel approach for sharing the initial quantum state privately between communicators, i.e., quantum encryption sharing, is proposed by utilizing the idea of quantum encryption. The proposed protocol uses EPR pairs as the private quantum key to encrypt and decrypt the traveling photons, which can be repeatedly used after rotation. Due to quantum encryption sharing, the public announcement on the state of the initial quantum state is omitted, thus the information leakage problem is overcome. The information-theoretical efficiency of the proposed protocol is nearly 100%, much higher than previous information leakage resistant quantum dialogue protocols. Moreover, the proposed protocol only needs single-photon measurements and nearly uses single photons as quantum resource so that it is convenient to implement in practice.     

Quantum Secure Dialogue with Quantum Encryption

How to solve the information leakage problem has become the research focus of quantum dialogue. In this paper, in order to overcome the information leakage problem in quantum dialogue, a novel approach for sharing the initial quantum state privately between communicators, i.e., quantum encryption sharing, is proposed by utilizing the idea of quantum encryption. The proposed protocol uses EPR pairs as the private quantum key to encrypt and decrypt the traveling photons, which can be repeatedly used after rotation. Due to quantum encryption sharing, the public announcement on the state of the initial quantum state is omitted, thus the information leakage problem is overcome.The information-theoretical efficiency of the proposed protocol is nearly 100%, much higher than previous information leakage resistant quantum dialogue protocols. Moreover, the proposed protocol only needs single-photon measurements and nearly uses single photons as quantum resource so that it is convenient to implement in practice.     

Quantum Correlations Evolution Asymmetry in Quantum Channels

It was demonstrated that the entanglement evolution of a specially designed quantum state in the bistochastic channel is asymmetric. In this work, we generalize the study of the quantum correlations, including entanglement and quantum discord, evolution asymmetry to various quantum channels. We found that the asymmetry of entanglement and quantum discord only occurs in some special quantum channels, and the behavior of the entanglement evolution may be quite different from the behavior of the quantum discord evolution. To quantum entanglement, in some channels it decreases monotonously with the increase of the quantum channel intensity. In some other channels, when we increase the intensity of the quantum channel, it decreases at first, then keeps zero for some time, and then rises up. To quantum discord, the evolution becomes more complex and you may find that it evolutes unsmoothly at some points. These results illustrate the strong dependence of the quantum correlations evolution on the property of the quantum channels.     

Blind Quantum Signature with Blind Quantum Computation

Blind quantum computation allows a client without quantum abilities to interact with a quantum server to perform a unconditional secure computing protocol, while protecting client’s privacy. Motivated by confidentiality of blind quantum computation, a blind quantum signature scheme is designed with laconic structure. Different from the traditional signature schemes, the signing and verifying operations are performed through measurement-based quantum computation. Inputs of blind quantum computation are securely controlled with multi-qubit entangled states. The unique signature of the transmitted message is generated by the signer without leaking information in imperfect channels. Whereas, the receiver can verify the validity of the signature using the quantum matching algorithm. The security is guaranteed by entanglement of quantum system for blind quantum computation. It provides a potential practical application for e-commerce in the cloud computing and first-generation quantum computation.     

Quantum Gate-Based Quantum Private Comparison

International Journal of Theoretical Physics - Many existing protocols of quantum private comparison (QPC) are often made up of quantum part and classical part, because they employ quantum...     

Quantum Spinor Structures for Quantum Spaces

A general theory of quantum spinor structures on quantum spaces is presented within the formalism of quantum principal bundles. Quantum analogs of basic objects of the classical theory are constructed: Laplace and Dirac operators, quantum versions of Clifford and spinor bundles, a Hodge *-operator, integration operators. Quantum phenomena are discussed, including an example of the Dirac operator associated to a quantum Hopf fibration.     

Quantum World with Quantum Time

Since the beginning of quantum mechanics there have been a lot of attempts to quantize time. In this paper we refer to the little known concept of quantum time proposed by E.Kapuscik [Hadronic J. 8 (1985) 75]. We analyze some properties of systems with quantum time. Moreover we comment and discuss the idea of quantum time.     

Quantum Communication Scheme Using Non-symmetric Quantum Channel

A theoretical quantum communication scheme based on entanglement swapping and superdense coding is proposed with a 3-dimensional Bell state and 2-dimensional Bell state function as quantum channel. quantum key distribution and quantum secure direct communication can be simultaneously accomplished in the scheme. The scheme is secure and has high source capacity. At last, we generalize the quantum communication scheme to d-dimensional quantum channel.     

量子噪音与量子Langevin方程

介绍了量子噪音和量子Langevin方程 ,并与经典噪音和经典Langevin方程进行了比较 .量子噪音来源于两种途径 ,第一种与经典噪音相似 ,第二种则起源于Heisengberg测不准原理 .同时 ,也简略给出了量子Langevin方程的推导.The properties of quantum noise and Langevin equation are discussed. Comparisons between the quantum noise and Langevin eqution and the classic one are presented. A brief derivation for quantum Langevin equation is showed. The quantum noise comes from two ways, namely, the way as same as that of classic noise and the Heisenberg uncertainty.     

Quantum metrology

The statistical error is ineluctable in any measurement. Quantum techniques, especially with the development of quantum information, can help us squeeze the statistical error and enhance the precision of measurement. In a quantum system, there are some quantum parameters, such as the quantum state, quantum operator, and quantum dimension, which have no classical counterparts. So quantum metrology deals with not only the traditional parameters, but also the quantum parameters. Quantum metrology includes two important parts： measuring the physical parameters with a precision beating the classical physics limit and measuring the quantum parameters precisely. In this review, we will introduce how quantum characters （e.g., squeezed state and quantum entanglement） yield a higher precision, what the research areas are scientists most interesting in, and what the development status of quantum metrology and its perspectives are.     

Duality Quantum Computers and Quantum Operations

We present a mathematical theory for a new type of quantum computer called a duality quantum computer that is similar to one that has recently been proposed. We discuss the nonunitarity of certain circuits of a duality quantum computer. We then discuss the relevance of this work to quantum operations and their convexity theory. This discussion is based upon isomorphism theorems for completely positive maps.     

Weakly Regular Quantum Grammars and Asynchronous Quantum Automata

In this paper, we define weakly regular quantum grammars (WRQG), regular quantum grammars (RQG), asynchronous quantum automata (AQA) and synchronous quantum automata (SQA). Moreover, we investigate the relationships between quantum languages generated by weakly quantum regular grammars and by asynchronous quantum automata. At the mean time, we discuss the relationships between regular quantum grammars and synchronous quantum automata. This work is supported by National Science Foundation of China (Grant No. 10571112) and 973 Program of China (No. 2002CB312200).     

量子相干

量子相干不仅是量子力学中的一个基本概念,同时也是重要的量子信息处理的物理资源.随着基于资源理论框架的量子相干度量方案的提出,量子相干度的量化研究成为近年来人们关注的一个热点问题.量子相干作为一种物理资源也十分脆弱,极容易受到环境噪声的影响而产生退相干,因此开放系统中的量子相干演化和保持也是人们广泛关注的课题.另外,量子相干在量子多体系统、量子热动力学、量子生物学等领域也有着潜在的应用价值.本文介绍量子相干度量的资源理论框架和基于该框架定义的相对熵相干性、l1范数相干性、基于量子纠缠的相干性、基于凸顶结构的相干性和相干鲁棒性等量子相干度量函数,概述开放系统中量子相干演化的动力学行为、典型信道的量子相干产生和破坏能力以及量子相干的冻结等现象,同时例举量子相干在Deutsch-Jozsa算法、Grover算法以及量子多体系统相变问题研究等方面的重要应用.量子相干研究仍处于快速发展之中,期望本综述能为该领域的发展带来启示.     

Three-Party Quantum Network Communication Protocols Based on Quantum Teleportation

By utilizing the delocalized correlation of entangled states in quantum information theory, a novel method on acknowledgments of quantum information among three-party is presented, and then two three-party quantum network communication protocols based on quantum teleportation are presented, namely, three-party stop-wait quantum communication protocol and three-party selective automatic repeat quantum communication protocol. In the two proposed protocols, the data frames composed of qubits are teleported via three-party quantum teleportation, the two receivers simultaneously receive quantum frames from the sender, and then return quantum acknowledgment frames or quantum negative acknowledgment frames via quantum entanglement channels. The sender simultaneously receives and deals with quantum acknowledgment frames and quantum negative acknowledgment frames from the two receivers, thus the processing delay on returning quantum frames is reduced. And due to the transience of transferring quantum information, the returning of quantum acknowledgment frames and quantum negative acknowledgment frames are completed instantaneously, the proposed protocols reduce the transmission delay and improve the communication efficiency. During the whole course of communications, the classical channels are only used to transmit the measurement message, so the burdens of classical channels are reduced.     

Quantum Ratchet in Disordered Quantum Walk

Symmetrically evolving discrete quantum walk results in dynamic localization with zero mean displacement when the standard evolution operations are replaced by a temporal disorder evolution operation. In this work we show that the quantum ratchet action, that is, a directed transport in standard or disordered discrete‐time quantum walk can be realized by introducing a pawl like effect realized by using a fixed coin operation at marked positions that is, different from the ones used for evolution at other positions. We also show that the combination of standard and disordered evolution operations can be optimized to get the mean displacement of order ∝ t (number of walk steps). This model of quantum ratchet in quantum walk is defined using only a set of entangling unitary operators resulting in the coherent quantum transport.     

Quantum Anti-Zeno Effect in Artificial Quantum Systems

In this paper, we study a quantum anti-Zeno effect （QAZE） purely induced by repetitive measurements for an artificial atom interacting with a structured bath. This bath can be artificially realized with coupled resonators in one dimension and possesses photonic band structure like Bloeh electron in a periodic potential. In the presence of repetitive measurements, the pure QAZE is discovered as the observable decay is not negligible even for the atomic energy level spacing outside of the energy band of the artificial bath. If there were no measurements, the decay would not happen outside of the band. In this sense, the enhanced decay is completely induced by measurements through the relaxation channels provided by the bath. Besides, we also discuss the controversial golden rule decay rates originated from the van Hove＇s singularities and the effects of the counter-rotating terms.     

Some Quantum States Prepared with Polynomial Quantum Circuit

The quantum state preparation involved in quantum information processing greatly depends on the quantum computer models. In this paper we give a novel scheme for some quantum states preparation without any decomposition of global quantum gates. Our circuit reduces the exponential CNOT gates to polynomial of qubit numbers, i.e., n(n?1)/2 without requirements of quantum register. And the depth is changed from the currently known exponential circuits to n blocks, or polynomial for its detailed implementation. This method is also useful for multi-level quantum systems and expected to help in designing and building large-scale quantum applications using present physical technologies.     

Quantum Logic for Quantum Computers

The following results obtained within a project of finding the algebra of statesin a general-purpose quantum computer are reported: (1) All operations of anorthomodular lattice, including the identity, are fivefold-defined; (2) there arenonorthomodular models for both quantum and classical logics; (3) there is afour-variable orthoarguesian lattice condition which contains all known orthoarguesianlattice conditions including six- and five-variable ones. Repercussions to quantumcomputers operating as quantum simulators are discussed.