Matched witness for multipartite entanglement

Entanglement criteria for multipartite entangled states are obtained by matching witnesses to multipartite entangled states. The necessary and sufficient criterion of separability for three qubit X states is given as an example to illustrate the procedure of finding a criterion. The result is utilized to obtain the noise tolerance of W state. The necessary and sufficient criteria of three partite separability and full separability for four qubit noisy cluster states, three partite separability for four qubit noisy GHZ states are obtained.     

Quantifying entanglement of two relativistic particles using optimal entanglement witness

In a recent paper, it was shown that the projections of a relativistic spin operator (RSO) massive spin-frac12{frac{1}{2}} particle on a world-vector which can be in timelike or null tetrad direction are proportional to the helicity or Bargman-Wigner (BW) qubit, respectively. Here we consider Lorentz transformations of two-particle states, which have been constructed both in helicity basis. For convenience, instead of using the superposition of momenta we use only two momentum eigenstates (p ₁ and p ₂) for each particle. Consequently, in 2D momentum subspace we describe the structure of one particle in terms of the four-qubit system. We present a new approach to quantification of relativistic entanglement based on entanglement witness (EW), which is obtained by a new method of convex optimization. In addition, Lorentz invariance of entanglement using BW qubit is also studied.     

Towards a NMR implementation of a quantum lattice gas algorithm

Recent theoretical results suggest that an array of quantum information processors communicating via classical channels can be used to solve fluid dynamics problems. Quantum lattice-gas algorithms (QLGA) running on such architectures have been shown to solve the diffusion equation and the nonlinear Burgers equations. In this report, we describe progress towards an ensemble nuclear magnetic resonance (NMR) implementation of a QLGA that solves the diffusion equation. The methods rely on NMR techniques to encode an initial mass density into an ensemble of two-qubit quantum information processors. Using standard pulse techniques, the mass density can then manipulated and evolved through the steps of the algorithm. We provide the experimental results of our first attempt to realize the NMR implementation. The results qualitatively follow the ideal simulation, but the observed implementation errors highlight the need for improved control.     

Experimental analysis and implementation of a multiscale wireless/wired networked control system

The aim of this paper is to discuss the flexibility and the performance of a multiscale wireless/wired networked control system (NCS). This NCS consists of three different types of dynamic systems (fast, medium, and slow clients) with distinct time scales. The experimental results verified the capability of the NCS to combine both the wired and wireless networks and the control capability of the NCS with various sampling periods. Compared to the original wired NCS, the average steady-state error of the fast client increased by 20% to 30% under the same conditions with the wireless NCS within the bandwidth-utilization (BU) threshold. From the analysis, the sampling period together with the BU and the number of clients will determine the time-delay and packet-loss levels and affect the stability and performance of the NCS in a complex correlated manner.     

Disappearance of entanglement: a topological point of view

We give a topological classification of the evolution of entanglement, particularly the different ways the entanglement can disappear as a function of time. Four categories exhaust all possibilities given the initial quantum state is entangled and the final one is not. Exponential decay of entanglement, entanglement sudden death and sudden birth can all be understood and visualized in the associated geometrical picture - the polarization vector representation. The entanglement evolution categories of any model are determined by the topology of the state space and the dynamical subspace, the limiting state and the memory effect of the environment. Transitions between these types of behaviors as a function of physical parameters are also possible. These transitions are thus of topological nature. The symmetry of the system is also important, since it determines the dimension of the dynamical subspace. We illustrate the general concepts with a visualizable model for two qubits, and give results for extensions to N-qubit GHZ states and W states.     

Mediation of entanglement and nonlocality of a single fermion

Entanglement is one of the most distinctive features of quantum mechanics and is now considered a fundamental resource in quantum information processing, such as in the protocols of quantum teleportation and quantum key distribution. In general, to extract its power in a useful form, it is necessary to generate entanglement between two or more quantum systems separated by long distances, which is not an easy task due to its fragility under environmental disturbance. Here, we propose a method to create entanglement between two distant fermionic particles, which never interact directly by using a third fermion to mediate the correlation. The protocol initiates with three indistinguishable fermions in a separable state, which are allowed to interact in pairs according to the Hong–Ou–Mandel effect. As a result, it is demonstrated that bipartite maximally entangled states can be generated with an efficiency of about 56%, which makes the method a potential candidate for practical quantum information applications. Furthermore, we use the same protocol to show how the mediator fermion exhibits nonlocal properties, giving a new insight on the long-standing discussion about nonlocality of a single particle.     

Exploring degrees of entanglement

In spite of a long history, the quantification of entanglement still calls for exploration. What matters about entanglement depends on the situation, and so presumably do the numbers suitable for its quantification. Regardless of situational complications, a necessary first step is to make available for calculation some quantitative measure of entanglement. Here we define a geometric degree of entanglement, distinct from earlier definitions, but in the case of bipartite pure states related to that proposed by Shimony (Ann N Y Acad Sci 755:675–679, 1995). The definition offered here applies also to multipartite mixed states, and a variational method simplifies the calculation. We analyze especially states that are invariant under permutation of particles, states that we call bosonic. Of interest to quantum sensing, for bosonic states, we show that no partial trace can increase a degree of entanglement. For some sample cases we quantify the degree of entanglement surviving a partial trace. As a function of the degree of entanglement of a bosonic 3-qubit pure state, we show the range of degree of entanglement for the 2-qubit reduced density matrix obtained from it by a partial trace. Then we calculate an upper bound on the degree of entanglement of the mixed state obtained as a partial trace over one qubit of a 4-qubit bosonic state. As a reminder of the situational dependence of the advantage of entanglement, we review the way in which entanglement combines with scattering theory in the example of light-based radar.     

Feedback control of quantum entanglement in a two-spin system

A pair of spins is the most simple quantum system that can exhibit entanglement: a nonclassical property that plays an essential role in quantum information technologies. In this paper, feedback control problems of a symmetric two-spin system conditioned on a continuous measurement are investigated. In order to make some useful formulas in stochastic control theory directly applicable, we first derive a two-dimensional representation of the system. We then prove that a feedback controller stabilizes an entangled state of the two spins almost globally with probability one. Furthermore, it is demonstrated that some entangled states, which correspond to nonequilibrium points of the dynamics, are globally stabilized via feedback in the sense that the mean distance from a target can be reduced to an arbitrarily small value.     

Study of a monogamous entanglement measure for three-qubit quantum systems

The entanglement quantification and classification of multipartite quantum states is an important research area in quantum information. In this paper, in terms of the reduced density matrices corresponding to all possible partitions of the entire system, a bounded entanglement measure is constructed for arbitrary-dimensional multipartite quantum states. In particular, for three-qubit quantum systems, we prove that our entanglement measure satisfies the relation of monogamy. Furthermore, we present a necessary condition for characterizing maximally entangled states using our entanglement measure.     

智能卡芯片中TDES密码电路的差分功耗攻击

使用相关性分析方法进行差分功耗攻击(DPA)实验,成功攻击了TDES密码算法。结果表明,相关性分析方法对简单的功耗模型具有很好的攻击效果且实施简单,对于HD功耗模型,获得TDES每一轮的圈密钥所需最少曲线条数仅为3 500条;同时,由于TDES和DES电路的实现结构相同,对两者进行DPA攻击的方法相同。     

On monogamy of four-qubit entanglement

Our main result is a monogamy inequality satisfied by the entanglement of a focus qubit (one-tangle) in a four-qubit pure state and entanglement of subsystems. Analytical relations between three-tangles of three-qubit marginal states, two-tangles of two-qubit marginal states and unitary invariants of four-qubit pure state are used to obtain the inequality. The contribution of three-tangle to one-tangle is found to be half of that suggested by a simple extension of entanglement monogamy relation for three qubits. On the other hand, an additional contribution due to a two-qubit invariant which is a function of three-way correlations is found. We also show that four-qubit monogamy inequality conjecture of Regula et al. (Phys Rev Lett 113:110501, 2014), in which three-tangles are raised to the power \(\frac{3}{2}\), does not estimate the residual correlations, correctly, for certain subsets of four-qubit states. A lower bound on residual four-qubit correlations is obtained.     

Equation of motion for entanglement

We review an evolution equation for quantum entanglement for 2 × 2 dimensional quantum systems, the smallest system that can exhibit entanglement, and extend it to higher dimensional systems. Furthermore, we provide statistical evidence for the equation’s applicability to the experimentally relevant domain of weakly mixed states.     

Experimental implementation of distributed flocking algorithm for multiple robotic fish

This paper presents the experimental implementation of a flocking algorithm for multiple robotic fish governed by extended second-order unicycles. Combing consensus protocols with attraction/repulsion functions, a flocking algorithm is proposed to make the agents asymptotically converge to swim with consistent velocities and approach the equilibrium distances to their neighbors. The LaSalle–Krasovskii invariance principle is applied to verify the stability of the system. Besides numerical simulations, platform simulations involving robotic fish kinematic constraint and control mechanism are shown. An experiment with three robotic fish is implemented to illustrate the effectiveness of the proposed flocking algorithm in the presence of external disturbance and boundary collision.     

Three-qubit entanglement generation of quantum states dissipating into a common environment

In this paper, we investigate the dynamics of entanglement of three-qubit states of a system dissipating into a common environment. By using the tripartite negativity as entanglement measure, our results imply that the three-qubit entanglement can be generated among the three qubits which have no interaction with each other, but interact with the common environment independently. From our analysis, we find that the three-qubit entanglement increases from zero to a stable value which varies with the size of the system with the increasing of the scaled time. Additionally, the extension of the entanglement generation to an arbitrary size of a subsystem is made and some discussion is given.     

Decoherence and entanglement degradation of a qubit-qutrit system in non-inertial frames

We study the effect of decoherence on a qubit-qutrit system under the influence of global, local and multilocal decoherence in non-inertial frames. We show that the entanglement sudden death can be avoided in non-inertial frames in the presence of amplitude damping, depolarizing and phase damping channels at lower level of decoherence. However, degradation of entanglement is seen due to Unruh effect. It is seen that for lower values of decoherence, the depolarizing channel heavily degrades the entanglement as compared to the amplitude damping and phase damping channels. Entanglement sudden birth is also seen in case of depolarizing channel. However, for higher values of decoherence parameters, amplitude damping channel dominantly degrades the entanglement of the hybrid system. Entanglement sudden death is not seen for any value of acceleration of the accelerated observer “Rob” in case of phase damping channel. Further more, a symmetrical behaviour of negativity is seen for depolarizing channel.     

Transferring multiqubit entanglement onto memory qubits in a decoherence-free subspace

Different from the previous works on generating entangled states, this work is focused on how to transfer the prepared entangled states onto memory qubits for protecting them against decoherence. We here consider a physical system consisting of n operation qubits and 2n memory qubits placed in a cavity or coupled to a resonator. A method is presented for transferring n-qubit Greenberger–Horne–Zeilinger (GHZ) entangled states from the operation qubits (i.e., information processing cells) onto the memory qubits (i.e., information memory elements with long decoherence time). The transferred GHZ states are encoded in a decoherence-free subspace against collective dephasing and thus can be immune from decoherence induced by a dephasing environment. In addition, the state transfer procedure has nothing to do with the number of qubits, the operation time does not increase with the number of qubits, and no measurement is needed for the state transfer. This proposal can be applied to a wide range of hybrid qubits such as natural atoms and artificial atoms (e.g., various solid-state qubits).     

Experimental implementation and analysis of a DNA computing readout method based on real-time PCR with TaqMan probes

A new readout approach for the Hamiltonian Path Problem (HPP) in DNA computing based on the real-time polymerase chain reaction (PCR) is experimentally implemented and analyzed. Several types of fluorescent probes and detection mechanisms are currently employed in real-time PCR, including SYBR Green, molecular beacons, and hybridization probes. In this study, real-time amplification performed using the TaqMan probes is adopted, as the TaqMan detection mechanism can be exploited for the design and development of the proposed readout approach. Double-stranded DNA molecules of length 140 base-pairs are selected as the input molecules, which represent the solving path for an HPP instance. These input molecules are prepared via the self-assembly of 20-mer and 30-mer single-stranded DNAs, by parallel overlap assembly. The proposed readout approach consists of two steps: real-time amplification in vitro using TaqMan-based real-time PCR, followed by information processing in silico to assess the results of real-time amplification, which in turn, enables extraction of the Hamiltonian path. The performance of the proposed approach is compared with that of conventional graduated PCR. Experimental results establish the superior performance of the proposed approach, relative to graduated PCR, in terms of implementation time.     

Non-Markovian entanglement dynamics of two qubits interacting with a common electromagnetic field

We study the non-equilibrium dynamics of a pair of qubits made of two-level atoms separated in space with distance r and interacting with one common electromagnetic field but not directly with each other. Our calculation makes a weak coupling assumption but no Born or Markov approximation. We write the evolution equations of the reduced density matrix of the two-qubit system after integrating out the electromagnetic field modes. We study two classes of states in detail: Class A is a one parameter family of states which are the superposition of the highest energy and lowest energy states, and Class B states which are the linear combinations of the symmetric and the antisymmetric Bell states. Our results for an initial Bell state are similar to those obtained before for the same model derived under the Born–Markov approximation. However, in the Class A states the behavior is qualitatively different: under the non-Markovian evolution we do not see sudden death of quantum entanglement and subsequent revivals, except when the qubits are sufficiently far apart. We provide explanations for such differences of behavior both between these two classes of states and between the predictions from the Markov and non-Markovian dynamics. We also study the decoherence of this two-qubit system.     

基于STM32 的“模块化”电子技术综合创新平台的设计与实现

设计了一款基于嵌入式系统 STM32 的“模块化”电子技术综合创新平台,包括 “口袋实验室式”STM32核心控制板和“电子积木”式功能模块。其中“电子积木”式功能模块主要包括输入与输出功能模块、显示功能模块、模拟电子技术功能模块、数字电子技术功能模块、电力电子技术模块、传感器类功能模块、执行机构功能模块、工业通信功能模块、智能家居模块等9大功能模块。满足模电、数电、电力电子、传感器、单片机、嵌入式及物联网技术等课程单项技能实训要求,还能够让学生利用STM32核心控制板和“电子积木”式功能模块,通过不同技术方案实现超声波测距等综合创新应用项目。通过平台的应用推广,学生的知识综合应用能力和创新能力明显提升,成效明显。