Nonclassical correlations from dissociation-time entanglement

We discuss a strongly entangled two-particle state of motion that emerges naturally from the double-pulse dissociation of a diatomic molecule. This state, which may be called dissociation-time entangled, permits the unambiguous demonstration of nonclassical correlations by violating a Bell inequality based on switched single-particle interferometry and only position measurements. We apply time-dependent scattering theory to determine the detrimental effect of dispersion. The proposed setup brings into reach the possibility of establishing nonclassical correlations with respect to system properties that are truly macroscopically distinct.     

Asymmetric Bidirectional Controlled Remote State Preparation by Using a Seven-Particle Entangled State

We demonstrate that a seven-particle entangled state can be used to realize the deterministic asymmetric bidirectional controlled remote state preparation. That is to say Alice can remotely prepare an arbitrary known single-particle state for Bob and at the same time Bob can remotely prepare an arbitrary known two-particle state for Alice with the help of the supervisor Charlie. In our scheme, only single-particle projective measurements and two-particle projective measurement are needed.     

Single-Particle Coherence and the Reciprocal of the Mean Quantum Fisher Information in Three-Particle Phase State

We investigate the relation between the single-particle coherence and the reciprocal of the mean quantum Fisher information (RMQFI) in three-particle phase state. It is shown that the phase state is a entangled state that it is useful for sub-shot-noise phase estimation sensitivity. The single-particle coherence and RMQFI have the similar behaviors.     

Microscopic model of superconductivity in carbon nanotubes

We propose the model of a manifold of one-dimensional interacting electron systems to account for the superconductivity observed in ropes of nanotubes. We rely on the strong suppression of single-particle hopping between neighboring nanotubes in a disordered rope and conclude that the tunneling takes place in pairs of electrons, which are formed within each nanotube due to the existence of large superconducting correlations. Our estimate of the transition temperature is consistent with the values that have been measured experimentally in ropes with about 100 metallic nanotubes.     

Long-distance quantum teleportation assisted with free-space entanglement distribution

Faithful long-distance quantum teleportation necessitates prior entanglement distribution between two communicated locations. The particle carrying on the unknown quantum information is then combined with one particle of the entangled states for Bell-state measurements, which leads to a transfer of the original quantum information onto the other particle of the entangled states. However in most of the implemented teleportation experiments nowadays, the Bell-state measurements are performed even before successful distribution of entanglement. This leads to an instant collapse of the quantum state for the transmitted particle, which is actually a single-particle transmission thereafter. Thus the true distance for quantum teleportation is, in fact, only in a level of meters. In the present experiment we design a novel scheme which has overcome this limit by utilizing fiber as quantum memory. A complete quantum teleportation is achieved upon successful entanglement distribution over 967 meters in public free space. Active feed-forward control techniques are developed for real-time transfer of quantum information. The overall experimental fidelities for teleported states are better than 89.6%, which signify high-quality teleportation.     

Full-field quantum correlations of spatially entangled photons

Spatially entangled twin photons allow the study of high-dimensional entanglement, and the Laguerre-Gauss modes are the most commonly used basis to discretize the single-photon mode spaces. In this basis, to date only the azimuthal degree of freedom has been investigated experimentally due to its fundamental and experimental simplicity. We show that the full spatial entanglement is indeed accessible experimentally; i.e., we have found practicable radial detection modes with negligible cross correlations. This allows us to demonstrate hybrid azimuthal-radial quantum correlations in a Hilbert space with more than 100 dimensions per photon.     

Exponentially decaying correlations in a gas of strongly interacting spin-polarized 1D fermions with zero-range interactions

We consider the single-particle correlations and momentum distributions in a gas of strongly interacting, spinless 1D fermions with zero-range interactions. This system represents a fermionic version of the Tonks-Girardeau gas of impenetrable bosons as it can be mapped to a system of noninteracting 1D bosons. We use this duality to show that the T = 0, single-particle correlations exhibit an exponential decay with distance. This strongly interacting system is experimentally accessible using ultracold atoms and has a Lorentzian momentum distribution at large momenta whose width is given by the linear density.     

EPR纠缠光束时域量子关联的实验验证

我们利用平衡零拍探测系统和数据采集系统直接测量了EPR纠缠光束信号光场与闲置光场正交分量之间的时域量子起伏,验证了其量子关联.通过对EPR纠缠光束中的一束光场进行延迟,验证了信号光与闲置光不同步时将导致量子关联减弱乃至消失.我们的实验结果为开展连续变量量子密钥分发、非高斯态的实验制备和纠缠纯化奠定了实验基础.     

Quantum correlations from local amplitudes and the resolution of the Einstein-Podolsky-Rosen nonlocality puzzle

The Einstein-Podolsky-Rosen (EPR) nonlocality puzzle has been recognized as one of the most important unresolved issues in the foundational aspects of quantum mechanics. We show that the problem is more or less entirely resolved, if the quantum correlations are calculated directly from local quantities, which preserve the phase information in the quantum system. We assume strict locality for the probability amplitudes instead of local realism for the outcomes and calculate an amplitude correlation function. Then the experimentally observed correlation of outcomes is calculated from the square of the amplitude correlation function. Locality of amplitudes implies that measurement on one particle does not collapse the companion particle to a definite state. Apart from resolving the EPR puzzle, this approach shows that the physical interpretation of apparently “nonlocal” effects, such as quantum teleportation and entanglement swapping, are different from what is usually assumed. Bell-type measurements do not change distant states. Yet the correlations are correctly reproduced, when measured, if complex probability amplitudes are treated as the basic local quantities. As examples, we derive the quantum correlations of two-particle maximally entangled states and the three-particle Greenberger-Horne-Zeilinger entangled state.     

Quantum Information Splitting of an Arbitrary Three-Qubit State Via a Seven-Qubit Maximally Entangled State

Recently Zha et al. (J. Phys. A: Math. Theor. 45:255–302 2012) have proposed a seven-particle maximally entangled state. In this paperwe propose a schemes for splitting three-qubit states by using seven-particle maximally entangled state as the quantum channel. After the sender performs Bell-basis measurements on her particles, and the cooperators operate single-particle measurements on their particles, the state receiver can reconstruct the original state of the sender by applying the appropriate unitary operation.     

Generation of entangled states of qudits using twin photons

We report an experiment to generate entangled states of D-dimensional quantum systems, qudits, by using transverse spatial correlations of two parametric down-converted photons. Apertures with D slits in the arms of the twin photons define the qudit space. By manipulating the pump beam correctly, the twin photons will pass only by symmetrically opposite slits, generating entangled states between these different paths. Experimental results for qudits with D = 4 and 8 are shown. We demonstrate that the generated states are entangled states.     

Interaction-Free Effects Between Distant Atoms

A Gedanken experiment is presented where an excited and a ground-state atom are positioned such that, within the former’s half-life time, they exchange a photon with 50% probability. A measurement of their energy state will therefore indicate in 50% of the cases that no photon was exchanged. Yet other measurements would reveal that, by the mere possibility of exchange, the two atoms have become entangled. Consequently, the “no exchange” result, apparently precluding entanglement, is non-locally established between the atoms by this very entanglement. This quantum-mechanical version of the ancient Liar Paradox can be realized with already existing transmission schemes, with the addition of Bell’s theorem applied to the no-exchange cases. Under appropriate probabilities, the initially-excited atom, still excited, can be entangled with additional atoms time and again, or alternatively, exert multipartite nonlocal correlations in an interaction free manner. When densely repeated several times, this result also gives rise to the Quantum Zeno effect, again exerted between distant atoms without photon exchange. We discuss these experiments as variants of interaction-free-measurement, now generalized for both spatial and temporal uncertainties. We next employ weak measurements for elucidating the paradox. Interpretational issues are discussed in the conclusion, and a resolution is offered within the Two-State Vector Formalism and its new Heisenberg framework.     

An Efficient and Economic Scheme for Remotely Preparing a Multi-Qudit State via a Single Entangled Qudit Pair

We propose some schemes for remote preparation of arbitraryhigh-dimensional equatorial entangled state via a single bipartitehigh-dimensional entangled state as quantum channel. We firstlypresent the remote preparation of bipartite three- and d-dimensionalequatorial entangled state by using a single entangled qutrit andqudit pair, respectively, and then directly generalize the schemesto multipartite case. The cases of the quantum channel beingnon-maximally two-qutrit and two-qudit entangled state are alsoconsidered, respectively. In these schemes the required resourcesare single-particle projective measurement, appropriate localunitary operation, auxiliary particle, and high-dimensional C-NOToperation. It is shown that the entanglement resource and classicalcommunication cost are both greatly reduced in our schemes.     

Fringe visibility for two qubits interacting with a macroscopic medium

We study both the two-particle and single-particle fringe visibility in the generalized version of the Nakazato–Pascazio model where two qubits interact with a finite length one-dimensional array.Both the two-particle and single-particle fringe visibilities are investigated with different initial states of the particles spin.For different initial states of the particles spin,the two-particle fringe visibility either decreases or increases over time,and may even decrease first and increase later.Due to the interaction between the particles and the one-dimensional array,the single-particle fringe visibility increases over time when the initial state of the two particles spin is independent.The single-particle fringe visibility is equal to 0 as the two-particle spin is initially in the completely entangled state or in the singlet state.     

Bose-Einstein condensation with an entangled order parameter

We propose a practically accessible non-mean-field ground state of Bose-Einstein condensation, which occurs in an interspecies two-particle entangled state, and is thus described by an entangled order parameter. A suitably defined entanglement entropy is used as the characterization of the non-mean-field nature, and is found to persist in a wide parameter regime. The interspecies entanglement leads to novel interference terms in the dynamical equations governing the single-particle orbital wave function. Experimental feasibility and several methods of probe are discussed. We urge the study of multichannel scattering between different species of atoms.     

Efficient Symmetric Five-Party Quantum State Sharing of an Arbitrary <Emphasis Type="Italic">m</Emphasis>-Qubit State

We present an efficient symmetric scheme for five-party quantum state sharing of an arbitrary m-qubit state with 2m three-particle entangled states. The implementations of this scheme only need to exploit the CNOT gate operations and the single-particle measurements, instead of the three-particle GHZ-state measurements, which makes it more convenient in a practical application than some previous schemes. In addition, its total efficiency can approach the maximal value in theory.     

Quantum correlations and secret bits

It is shown that (i) all entangled states can be mapped by single-copy measurements into probability distributions containing secret correlations, and (ii) if a probability distribution obtained from a quantum state contains secret correlations, then this state has to be entangled. These results prove the existence of a two-way connection between secret and quantum correlations in the process of preparation. They also imply that either it is possible to map any bound entangled state into a distillable probability distribution or bipartite bound information exists.     

Schemes for Splitting Quantum Information with Four-Particle Genuine Entangled States

We propose two schemes for splitting single- and two-qubit states by using four-particle genuine entangled state as the quantum channel. After the sender performs Bell-basis （or three-partite GHZ- basis） measurements on her particles, and the cooperators operate single-particle measurements on their particles, the state receiver can reconstruct the original state of the sender by applying the appropriate unitary operation. In particular, in the scheme for splitting two-qubit state, the receiver needs to introduce an auxiliary particle and carries out a C-NOT operation.     

Remote Preparation of a Two-Particle Entangled State via Two Tripartite <Emphasis Type="Italic">W</Emphasis> Entangled States

We present a scheme for remotely preparing a general two-particle entangled state via two tripartite W entangled states of different amplitudes. In this scheme one sender and two remote receivers are involved. The sender can help either one of the receivers to remotely reconstruct the original state with the aid of the other receiver’s two single-particle orthogonal measurements. It is shown that by means of the method of the positive operator-valued measurement, our remote state preparation scheme can be achieved probabilistically. This project supported by the National Key Basic Research and Development Program of China under Grant No. 2006CB921604 and the National Natural Science Foundation of China under Grant Nos. 60578050 and 10434060.     

Universal Three-Party Quantum Secret Sharing Against Collective Noise

we present a robust and universal quantum secret sharing protocol with four-qubit decoherence-free (DF) states against collective noise. The transmission's safety is ensured by the nonorthogonality of the noiseless states traveling on the quantum channel. Although this scheme uses entangled states for encoding, only single-particle product measurements are required.