Creation of Multipartite Entanglement and Entanglement Transfer via Heisenberg Interaction

We discuss how to create multipartite entanglement. By coupling a new particle with entangled particles via Heisenberg interaction between two particles, we can prepare three-particle entangled states. For some special coupling strength, entanglement transfer can be achieved from entangled pair AB to particles A and C that never interact by coupling particle C with particle B, which can be used to create entanglement between two separated particles.     

Spin-photon Entanglement in Spontaneous Emission

The two-pathway decay, spin-photon entanglement, and spontaneous generated spin coherence in a Lambdatype three-level system can be understood in a unified picture in terms of quantum entanglement of the electron spin, the photon polarization, and the photon waveform. Within such a unified picture, the spontaneous emission can be controlled to present a designated effect by external field, optical excitation, and quantum measurement. Various experiments are proposed to implement such control, with some of them already realized.     

Faithful Telecloning with Multiparticle Entanglement

We study the 1→N faithful telecloning of two linear-independent states of a one-qubit system.Based on the analysis of the probabilistic cloning machine,we construct a multiparticle entangled state,and present a telecloning scheme under local operations and classical communication (LOCC).The success probability is greater than half of the optimal probability of the probabilistic cloning machine.Specifically,we show how to prepare the three-particle entangled state meeded by 1→2 telecloning under LOCC using the Greenberger-Horne-Zeilinger state as a resource.All the operations in 1→2 telecloning are within the reach of current technology.     

Probabilistic Preparation of N—particle Cat States via Entanglement Swapping and Entanglement Concentration

We discuss two different schemes for the probabilistic preparation of N-particle cat states using pure multiparticle entangled states via entanglement swapping and entanglement concentration.At the centre of distribution A,Alice performs all of the operations required to achieve our goal.     

Deterministic Secure Communication Without Using Entanglement

We show a deterministic secure direct communication protocol using single qubit in a mixed state. The security of this protocol is based on the security proof of BB84 protocol. It can be realized by the current technologies.     

Explicit Protocol for Deterministic Entanglement Concentration

We present an explicit protocol for extraction of an EPR pair from two partially entangled pairs in a deterministic fashion via local operations and classical communication. This protocol is constituted by a local measurement described by a positive operator-valued measure (POVM), one-way classical communication, and a corresponding local unitary operation or a choice between the two pairs. We explicitly construct the required POVM by the analysis of the doubly stochastic matrix connecting the initial and the final states. Our scheme might be useful in future quantum communication.     

Entanglement Swapping and Quantum Correlation Transferring

We report the experimentally realization of entanglement swapping and quantum correlation transferring for continuous variables. The initial entangled states are generated from two non-degenerate optical parametric amplifiers （OPA） operating at de-amplification pumped. Two beams from each OPAs are entangled through implementing the directly measurement of Bell state between other two beams. The quantum correlation degrees of 1.23 and 1. 12 dB below the shot noise limit for the amplitude and phase quadratures resulting from the entanglement swapping are measured straightly. The quantum correlation transferring is experimentally demonstrated with two quantum correlated twin beams. The initial correlated twin beams are generated from two separated non- degenerate OPO pumped by independent laser. The intensity quantum correlation degree of 1dB below SNL from the transferring is measured.     

Entanglement and it’s Manipulation

In this paper, we substantiate the at very low temperatures entanglement is exhibited manifestly. Also, we show that the phenomena of entanglement can be manipulated with respect to certain parameters in 2D crystals like graphene.

     

Critical Scaling Behaviors of Entanglement Spectra

We investigate the evolution of entanglement spectra under a global quantum quench from a short-range correlated state to the quantum critical point.Motivated by the conformal mapping,we find that the dynamical entanglement spectra demonstrate distinct finite-size scaling behaviors from the static case.As a prototypical example,we compute real-time dynamics of the eritanglement spectra of a one-dimensional transverse-field Ising chain.Numerical simulation confirms that the entanglement spectra scale with the subsystem size I as for the dynamical equilibrium state,much faster thanαIn^-1 l for the critical ground state.In particular,as a byproduct,the entanglement spectra at the long time limit faithfully gives universal tower structure of underlying Ising criticality,which shows the emergence of operator-state correspondence in the quantum dynamics.     

Simple Algorithm for Deterministic Entanglement Concentration

We first present the general solution and the simplest special solution of the doubly stochastic matrix used in deterministic entanglement concentration. Then, we give a better scheme to realize deterministic entanglement concentration. Under this scheme, the concentration is realized, and more importantly, two partially entangled pairs concentrate to four-particle Greenberger-Horne-Zeilinger （GHZ） states with a certain probability.     

Entanglement transfer via the Raman atom-cavity-field interaction

For the Raman interaction between an atom and a two-mode cavity field prepared in the state |01> or |10> , the atom and the field can be disentangled periodically. Such a property of Raman atom-field interaction allows the full entanglement transfer among many atoms and bimodal cavities. In the calculations, each atom is assumed to interact with its own cavity at a different time and so non-identical atoms can be treated conveniently. Entanglement sudden death is discussed too. Though atom-field interaction greatly changes the values of the concurrence for two atoms, configuration of the concurrence is almost not affected. When there is entanglement sudden death, atoms and cavities can still be entangled with one another. However, full entanglement transfer cannot be achieved for such systems with Raman atom-field interaction.     

Entanglement COncentration of Entangled Squeezed Vacuum States

By analysing the action of a beamsplitter on squeezed vacuum states(SVSs),it is found that,if the two input light beams of the beamsplitter have the same squeezing amplitude and phase,the output state is a two-mode SVS,If the two input light beams of the beamsplitter have the same squeezing amplitude but a phase difference of π,the output state is a direct porduct state of two single-mode SVS.Based on these results,we propose to distill a maximally entangled SVS from a partially entangled SVS by using a 50/50 beamsplitter and photodetectors.     

Squeezing and Entanglement in Continuous Variable Systems

Based on total variance of a pair of Einstein-Podolsky-Rosen (EPR) type operators, the generalized EPR entangled states in continuous variable systems are defined. We show that such entangled states must correspond to two-mode squeezing states whether these states are Gaussian or not and whether they are pure or not. With help of the relation between the total variance and the entanglement, the degree of such entangIement is also defined. Through analysing some specific cases, we see that this method is very convenient and easy in practical applications. In addition, an entangled state with no squeezing is studied, which reveals that there certainly exists something unknown about entanglement in continuous variable systems.     

Stability of Pairwise Entanglement in Decoherence Environment

Consider the dynamics of a bipartite entangled system in the decoherence environment, we investigate the stability of pairwise entanglement under decoherence.We find that with the same initial entanglement, the lifetime of entanglement in pure states and some mixed states is the longest.We call these special entangled states as Decoherence Path States (DPS).Besides, we present simple analytic evolution equations of the entanglement in these states.The lifetimes can also be obtained easily.Furthermore, we also study the stability of the nearest neighbor entanglement in the ground state of an antiferromagnetic spin-1/2 ring.Coincidentally, the conclusion is that it is as stable as Decoherence Path States.Thus the nearest neighbor entanglement in the ground state is not maximized but it is the most stable.This interesting result links the energy and entanglement in a spin system from a new point of view.     

Experimental Creation of Entanglement Using Separable States

We experimentally demonstrate that the entanglement can be created on two distant particles using separable states. We show that two working particles can share some entanglement, while one ancilla particle always remains separable from the two working particles during the experimental evolution of the system. Our experiment can be viewed as a benchmark to illustrate the idea that no prior entanglement is necessary to create entanglement.     

Block Entanglement in the Single-Hole Hubbard Model

We investigate the distribution of the entanglement of the one-dimensional single-hole Hubbard model （HM） and study the relationship between the entanglement and quantum phase transition in the model. The von Neumann entropy of a block with neighbouring spins L for a single-hole HM is calculated using the densitymatrix renormalization group. The distributions of the entanglement entropy in the ground state, as a function of block length, show a dramatic effect, i.e. effectively decoupling with the centres, no matter how the Coulomb interaction u 〉0 or u 〈0. Contrarily, for the Coulomb interaction u = 0 or close to zero, the entanglement entropy in the single-hole model reaches a saturation value for a certain block size. For a fixed size L = 40, the ground state entanglement entropy measure, as a function of u1 shows a peak corresponding to the critical quantum phase transition.     

Correlated Emission Laser as an Entanglement Amplifier

We consider a two-photon correlated emission laser as a source of an entangled radiation with a large number of photons in each mode. The system consists of three-level atomic schemes inside a doubly resonant cavity. We study the dynamics of this system in the presence of cavity losses, concluding that the creation of entangled states with photon numbers up to tens of thousands seems achievable.     

Remote State Preparation with Genuine Multipartite Entanglement

Enlightened by the work of Yeo and Chua [Phys. Rev. Lett. 96 （2006） 060502] for teleportation and dense coding with genuine multipartite entanglement, we present an explicit protocol for faithful remote state preparation in a real coefficient case by using the same four-particle entangled state which is not reducible to pair of Bell states. It is shown that any complex coefficient case can be changed to a real coefficient case. With this protocol, the state can play an analogous role to Einstein-Podolsky-Rosen pairs in the theory of multipartite entanglement.