量子信息系统发展探讨

量子信息系统是技术形态量子化的信息系统,具体表现为量子信息技术在信息获取、信息存储、信息传递、信息处理、信息使用等信息过程中的应用。研究发现量子信息系统的特征包括更加丰富的信息量、更加快速的信息处理以及增强的信息安全。相关系统应用集中在量子保密通信、量子计算模拟和量子精密测量等方向。量子信息技术将促进感知、计算、存储、通信、应用等过程的一体化融合,颠覆电子信息系统是一个大概率事件。

量子态和量子测量态的特性与应用

量子信息技术是基础性创新,是信息技术发展的颠覆性前沿。面向量子信息技术应用,研究工作阐述了量子态的离散性、随机性、叠加性、纠缠性等四个关键特性,提出了量子测量态的离散性、概率性、多样性、关联性等四个对应特征,描述了这些特性在当前以及未来量子信息系统中的应用场景和目标,并按照这些特性的应用程度给出了量子信息系统代际划分。研究工作通过分析量子态和量子测量态的特性,在量子信息科学与量子信息工程应用之间架起了一座桥梁,对量子信息技术在信息感知、信息存储、信息处理、信息传递、信息应用等信息过程中的创新应用具有重要意义。

量子信息讲座续讲 第二讲 量子信息安全系统

详细介绍了量子密码的相关内容 ,包括量子密码理论基础、量子保密系统、量子认证系统、量子密码与其他学科的关系以及量子密码的应用与展望 。

Witnessing quantum phase transition in a non-Hermitian trapped ion system via quantum Fisher information

Quantum Fisher information is used to witness the quantum phase transition in a non-Hermitian trapped ion system with balanced gain and loss,from the viewpoint of quantum parameter estimation.We formulate a general non-unitary dynamic of any two-level non-Hermitian system in the form of state vector.The sudden change in the dynamics of quantum Fisher information occurs at an exceptional point characterizing quantum criticality.The dynamical behaviors of quantum Fisher information are classified into two different ways which depends on whether the system is located in symmetry unbroken or broken phase regimes.In the phase regime where parity and time reversal symmetry are unbroken,the oscillatory evolution of quantum Fisher information is presented,achieving better quantum measurement precision.In the broken phase regime,quantum Fisher information undergoes the monotonically decreasing behavior.The maximum value of quantum estimation precision is obtained at the exceptional point.It is found that the two distinct kinds of behaviors can be verified by quantum entropy and coherence.Utilizing quantum Fisher information to witness phase transition in the non-Hermitian system is emphasized.The results may have potential applications to non-Hermitian quantum information technology.

Controlled Coherent Quantum Tunneling of Atomic Ensembles

We investigate the coherent tunneling phenomenon of the laser-driven atomic ensembles confined in a well-separated double-well potential. By generalizing the Frohlich canonical transformation to adiabatically eliminate the light field variable, a BCS-like effective Hamiltonian is obtained to depict the residual interaction between the two atomic ensembles. The number of the tunneling collective low excitations and its relationship to the ratios gr/gl and Nr/Nl are given.

Generalized Quantum Games with Nash Equilibrium

We define generalized quantum games by introducing the coherent payoff operators and propose a simple scheme to illustrate it.The scheme is implemented with a single spin qubit system and a two-entangled-qubit system.The Nash Equilibrium Theorem is proved for the models.

Two-Step Deterministic Remote Preparation of an Arbitrary Quantum State

We present a two-step deterministic remote state preparation protocol for an arbitrary qubit with the aid of a three-particle Greenberger-Horne-Zeilinger state. Generalization of this protocol for higher-dimensional Hilbert space systems among three parties is also given. We show that only single-particle yon Neumann measurements, local operations, and classical communication are necessary. Moreover, since the overall information of the quantum state can be divided into two different pieces, which may be at different locations, this protocol may be useful in the quantum information field.

Bipartite Entanglement Dynamics in Three Qubits System with Dzyaloshinskii-Moriya Interaction

We investigate the bipartite entanglement dynamics of the system composed by three qubits A,B,and C.There is no interaction between A and B,and that of C and B is Dzyaloshinskii-Moriya (DM) spin-orbit interaction.We find that the purity of qubits A and B and the initial state of the qubit C are the two effective parameters tocontrol the entanglement dynamics of the bipartite subsystems.This study sheds some lights on the control of quantumentanglement,which would be helpful for quantum information processing.

Quantum Information Transfer from a Double Quantum Dot System to a Cavity Field

In this paper, we propose a scheme to realize quantum information transfer from a double quantum dot （DQD） system to a quantized cavity field. The DQD and the cavity field are treated as a two-state charge qubit and a continuous-variable system, respectively. It is shown that quantum information encoded in the two-state DQD system can be transferred to quantum states of the cavity field with a continuous-variable basis through appropriate projective measurements with respect to the DQD.

A Comparative Study of Quantum and Classical Deletion

Here in this letter, we study the difference between quantum and classical deletion. We point out that the linear mapping deletion operation used in the impossibility proof for quantum systems applies also to classical system. The general classical deletion operation is a combined operation of measurement and transformation, i.e., first read the state and then transfer the state to the standard blank state. Though both quantum information and classical information can be deleted in an open system, quantum information cannot be recovered while classical information can be recovered.

Application of Y(sl(2)) Algebra for Entanglement of Two-Qubit System

We construct the transition operators in terms of the generators of the general Yangian and the reduced Yangian. By acting these operators on a two-qubit pure state, we find that the entanglement degrees of the states are all decreased from the certain values to zero for the reduced Yangian algebra, which makes the state disentangled. This result sheds new light on the physical meaning of Y （sl（2） ） in quantum information.

Non-Markovian discrete qubit dynamics

The study of open quantum systems is important for fundamental issues of quantum physics as well as for technological applications such as quantum information processing. The interaction of a quantum system with its environment is usually detrimental for the quantum properties of the system and leads to decoherence. However,sometimes a quantum control can lead to a coherent partial exchange of information between the system and the dynamics of the open system might become non-Markovian. In this article, we study experimentally discrete nonMarkovian open quantum system dynamics. We implement a local control protocol using linear optics for controlling the information flow between the open system and the environment. We show how the transition from Markovian to non-Markovian dynamics can be controlled using only local operations for the open system.

Efficient nonlocal two-step entanglement concentration protocol for three-level atoms in an arbitrary less-entangled W state using cavity input-output process

We present an efficient two-step entanglement concentration protocol(ECP)for three-level atoms trapped in one-sided optical micro-cavities in an arbitrary three-particle less-entangled W state,using the coherent state input-output process in low-Q cavity quantum electrodynamics system.In each step of the new proposed protocol,one of the three remote users prepares the auxiliary coherent optical pulses to perform cavity input-output process and then utilizes the standard homodyne measurement to discriminate the final outgoing coherent states.When both of the two steps are successful,remote parties can deterministically concentrate the less-entangled W state atoms to a standard maximally entangled W state.Compared with previous ECPs for W state,this protocol has some advantages and can be widely used in current quantum repeater and some quantum information processing tasks.

Separability criteria via some classes of measurements

Mutually unbiased bases (MUBs) and symmetric informationally complete (SIC) positive operator-valued measurements (POVMs) are two related topics in quantum information theory. They are generalized to mutually unbiased measurements (MUMs) and general symmetric informationally complete (GSIC) measurements, respectively, that are both not necessarily rank 1. We study the quantum separability problem by using these measurements and present separability criteria for bipartite systems with arbitrary dimensions and multipartite systems of multi-level subsystems. These criteria are proved to be more effective than previous criteria especially when the dimensions of the subsystems are different. Furthermore, full quantum state tomography is not needed when these criteria are implemented in experiment.

Generation of a genuine six-partite entangled state in trapped-ion system

Recently, a genuine six-qubit entangled state Isix） has been proposed [Chen P X, et al. Phys Rev A, 2006, 74： 032324]. This state does not belong to the well-known three types of multipartite entangled states, i.e., Greenberger-Home-Zeilinger （GHZ） state, W state, and linear cluster state. This state has many potential applications in quantum information processing. We pro- pose a scheme for generating such a genuine six-qubit entangled state for trapped ions in thermal motion. The scheme is insen- sitive to both the initial motional state and heating.

Qubit Systems from Colored Toric Geometry and Hypercube Graph Theory

We develop a new geometric approach to deal with qubit information systems using colored graph theory. More precisely, we present a one to one correspondence between graph theory, and qubit systems, which may be explored to attack qubit information problems using torie geometry considered as a powerful tool to understand modern physics including string theory. Concretely, we examine in some details the cases of one, two, and three qubits, and we find that they are associated with CP1, CP1×CP1 and CP1×CP1× CP1 toric varieties respectively. Using a geometric procedure referred to as a colored toric geometry, we show that the qubit physics can be converted into a scenario handling toric data of such manifolds by help of hypercube graph theory. Operations on toric information can produce universal quantum gates.

Quantum measurement in coherence-vector representation

We consider the quantum measurements on a finite quantum system in coherence-vector representation. In this representation, all the density operators of an N-level(N≥2) quantum system constitute a convex set M^(N)embedded in an(N^2- 1)-dimensional Euclidean space R^((N^2)-1), and we find that an orthogonal measurement is an(N- 1)-dimensional projector operator on R^((N^2)-1). The states unchanged by an orthogonal measurement form an(N- 1)-dimensional simplex, and in the case when N is prime or power of prime, the space of the density operator is a direct sum of(N + 1) such simplices. The mathematical description of quantum measurement is plain in this representation, and this may have further applications in quantum information processing.

Quantum state and process tomography via adaptive measurements

We investigate quantum state tomography(QST) for pure states and quantum process tomography(QPT) for unitary channels via adaptive measurements. For a quantum system with a d-dimensional Hilbert space, we first propose an adaptive protocol where only 2d. 1 measurement outcomes are used to accomplish the QST for all pure states. This idea is then extended to study QPT for unitary channels, where an adaptive unitary process tomography(AUPT) protocol of d2+d.1measurement outcomes is constructed for any unitary channel. We experimentally implement the AUPT protocol in a 2-qubit nuclear magnetic resonance system. We examine the performance of the AUPT protocol when applied to Hadamard gate, T gate(/8 phase gate), and controlled-NOT gate,respectively, as these gates form the universal gate set for quantum information processing purpose. As a comparison, standard QPT is also implemented for each gate. Our experimental results show that the AUPT protocol that reconstructing unitary channels via adaptive measurements significantly reduce the number of experiments required by standard QPT without considerable loss of fidelity.

Dynamical Change of Quantum Fisher Information of Cavity-Reservoir Systems

We study the quantum Fisher information(QFI) dynamics of the phase parameter in the enlarged cavityreservoir systems at zero temperature under two situations of large N limit and non-Markovian environment,respectively.We find an important relation that the total quantities of QFI of the cavity and reservoir are equal to unit during the dynamical evolution.The lost QFI of the cavity transfers to its corresponding reservoir with the same quantities simultaneously.Moreover,we also find that the detuning parameter and non-Markovian effect are two significant factors to affect the preservation of QFI.