W-type States Research Articles

Efficient generation of Bell and W-type states in cavity QED

Two generation schemes for Bell and W-type states of single-photon in cavity QED are proposed. The proposed schemes are simple and efficient in the sense that it requires no measurements on the particles.

Faithful Controlled Teleportation of an Arbitrary Unknown Two-Atom State via Special W-States and QED Cavity

A scheme is proposed for the controlled teleportation of an arbitrary two-atom state via special W-type entangled states and QED cavity. The scheme does not involve the direct joint Bell-state-measurement (BSM). We show that the quantum information is split into two parts, thus the original atomic state cannot be perfectly restored by the receiver without the other agent's collaboration and classical communication. In addition, the physical realization of this scheme is not difficult.

Scheme for splitting quantum information via W states in cavity QED systems

Assisted by multipartite entanglement, Quantum information may be split so that the original qubit can be reconstructed if and only if the recipients cooperate. This paper proposes an experimentally feasible scheme for splitting quantum information via W-type entangled states in cavity QED systems, where three-level Rydberg atoms interact with nonresonant cavities. Since W-type states are used as the quantum channel and the cavities are only virtually excited, the scheme is easy to implement and robust against decoherence, and the dependence on the quality factor of the cavities is greatly reduced.

制备行波光场的三模W型纠缠相干态

We propose a scheme for generation of three-mode W-type entangled coherent states (ECSs) in free-travelling optical fields by using a single-photon source, coherent state sources, beam splitters, photodetectors, and three-mode cross-Kerr media. The scheme consists of a Mach-Zehnder interferometer (MZI) in which each arm contains a cross-Kerr medium. We calculate the success probability of the generated W-type ECSs, and the total success probability is unity under the ideal conditions.

Near-deterministic generation of four-mode W-type entangled coherent states

In this paper, we propose an optical scheme to generate four-mode W-type entangled coherent states (ECSs) in free travelling optical fields by using a single-photon source, coherent state sources, beam splitters, photodetectors and cross-Kerr media. Our scheme consists of a symmetric optical setup in which there are two Mach–Zehnder interferometers in which each arm contains a cross-Kerr medium. We calculate the average fidelity of generated W-type ECSs, the success probability of producing four-mode W-type ECSs and the average fidelity of the generated four-mode W-type ECSs. It is indicated that our protocol is nearly deterministic.

Lower bounds for the fidelity of entangled-state preparation

Estimating the fidelity of state preparation in multiqubit systems is generally a time-consuming task. Nevertheless, this complexity can be reduced if the desired state can be characterized by certain symmetries measurable with the corresponding experimental setup. In this paper we give simple expressions to estimate the fidelity of multiqubit state preparation for rotational-invariant, stabilizer, and generalized coherent states. We specifically discuss the GHZ-type and W-type states, and obtain efficiently measurable lower bounds for the fidelity. We use these techniques to estimate the fidelity of a quantum simulation of an Ising-like interaction model using two trapped ions. These results are directly applicable to experiments using fidelity-based entanglement witnesses, such as quantum simulations and quantum computation.

Analytical treatment of W-state preparation in cavity QED in the presence of very weak dissipation

We propose an analytical treatment method of generation of multipartite W-type states with a single-resonant interaction of the atoms with the cavity mode in cavity QED, under the consideration of very weak decay from the excited atomic level and from the cavity mode. By manipulating different coupling strengths between the atoms and the cavity mode, we show how to deterministically produce W states, including the standard W state and the one with arbitrary coefficients. The corresponding analytical expressions are given, indicating that the detrimental influence from the atomic spontaneous emission is three times that from the cavity decay. The experimental feasibility of our scheme is also discussed by using current cavity QED techniques.

Generation of W-Type Entangled Coherent States of Three-Cavity Fieldsby a Driving Classical Field

A scheme is proposed to generate the W-type entangled coherent states ofthree-cavity field. The scheme is based on the resonant atom-fieldinteraction, thus the interaction time between the atom and the cavity isgreatly reduced, which is important in view of decoherence. Furthermore,the scheme does not need accurate adjustment of the interaction time.

Multi-photon entangled states from two-crystal geometry parametric down-conversion and their application in quantum teleportation

In this paper, we show that two kinds of W-type entangled states can be generated from a non-degenerate two-crystal geometry parametric down-conversion and they are very useful for quantum teleportation and quantum cloning. We also show that quantum teleportation of unknown one-particle state from a sender to either one of three receivers can be realized probabilistically by using the four-photon entangled state directly from a degenerate two-crystal geometry parametric down-conversion.

Optimal processing of quantum information viaW-type entangled coherent states

Optimized probabilistic teleportation and remote symmetric entangling of an arbitrary logical qubit are studied using particular forms of W-type entangled coherent states. Of interest is the fact that, while the teleportation can alternatively be performed by the GHZ-type entangled coherent states, the remote symmetric entangling strictly requires those of the W type.

W-type entanglement of distant atoms: conditional preparation

A scheme for preparing W-type entanglement is studied; it uses three trapped atoms in leaky cavities. A Raman interaction is used to entangle the electronic levels and the quantized cavity field in each ion–cavity system. The output fields of the three cavities are superimposed and detected by three photodetectors. An entangled W-type three-atom state can be obtained, conditioned on the records of the photodetectors.

On the geometry of entangled states

The basic question that is addressed in this paper is finding the closest separable state for a given entangled state, measured with the Hilbert-Schmidt distance. While this problem is in general very difficult, we show that the following strongly related problem can be solved: find the Hilbert-Schmidt distance of an entangled state to the set of all partially transposed states. We prove that this latter distance can be expressed as a function of the negative eigenvalues of the partial transpose of the entangled state, and show how it is related to the distance of a state to the set of positive, partially transposed (PPT) states. We illustrate this by calculating the closest biseparable state to the W state and give a simple and very general proof for the fact that the set of W-type states is not of measure zero. Next we show that all surfaces with states whose partial transposes have constant minimal negative eigenvalue are similar to the boundary of PPT states. We illustrate this with some examples on bipartite qubit states, where contours of constant negativity are plotted on two-dimensional intersections of the complete state space.

Classification of mixed three-qubit states.

We introduce a classification of mixed three-qubit states, in which we define the classes of separable, biseparable, W, and Greenberger-Horne-Zeilinger states. These classes are successively embedded into each other. We show that contrary to pure W-type states, the mixed W class is not of measure zero. We construct witness operators that detect the class of a mixed state. We discuss the conjecture that all entangled states with positive partial transpose (PPTES) belong to the W class. Finally, we present a new family of PPTES "edge" states with maximal ranks.