Arbitrary Entangled State Research Articles

One-step generation of multipartite entanglement among nitrogen-vacancy center ensembles.

We describe a one-step, deterministic and scalable scheme for creating macroscopic arbitrary entangled coherent states (ECSs) of separate nitrogen-vacancy center ensembles (NVEs) that couple to a superconducting flux qubit. We discuss how to generate the entangled states between the flux qubit and two NVEs by the resonant driving. Then the ECSs of the NVEs can be obtained by projecting the flux qubit, and the entanglement detection can be realized by transferring the quantum state from the NVEs to the flux qubit. Our numerical simulation shows that even under current experimental parameters the concurrence of the ECSs can approach unity. We emphasize that this method is straightforwardly extendable to the case of many NVEs.

Deterministic transmission of an arbitrary single-photon polarization state through bit-flip error channel

We present two error-tolerance transmission protocols of a single-photon polarization state when bit-flip error is taken into account. For achieving the transmission target of the single-photon state, the first protocol needs to encode it to a nonmaximally entangled Bell state. Exploiting the interaction of the polarization entanglement with spatial entanglement between two photons, its success probability is 100 %. Different from the first protocol, the second one utilizes the idea of teleportation with an auxiliary Bell state. By performing quantum nondemolition measurement to analyze the parity, conventional measurement, and unitary transformation operations, the success probability of the second protocol is approximately unity. Furthermore, the second protocol can be generalized to the error-tolerance transmission of an arbitrary mixed state or the distribution of an arbitrary multi-photon entangled state.

Entangled-state engineering of vibrational modes in a multimembrane optomechanical system

We propose an efficient method to generate entangled states of vibrational modes of membranes which are coupled to a single-mode cavity field via the radiation pressure. By using sideband excitations, we show that arbitrary entangled states of vibrational modes in different membranes can be produced in principle by sequentially applying a series of classical pulses with desired frequencies, phases, and durations. As examples, we show how to synthesize several typical entangled states, such as Bell states, NOON states, Greenberger-Horne-Zeilinger states, and W states. The environmental effect, information leakage, and experimental feasibility are briefly discussed. Our proposal can be applied to different setups of optomechanical systems, in which vibrating modes of many mechanical resonators are coupled to a single-mode cavity.

A Note on Resistance of NPT to Mixture of Separable States

We study the stability of NPT property of an arbitrary pure entangled state under the mixture of arbitrary pure separable states. For bipartite pure states with Schmidt number $n$ $(n>1)$ which is NPT, we show that this state is still NPT when it is mixed with no more than $\frac{n(n-1)}{2}-1$ arbitrary pure separable states. This result is generalized to multipartite case.

Generation of arbitrary symmetric entangled states with conditional linear optical coupling

An approach for generating the entangled photonic states |F1,F2>+|F2,F1> from two arbitrary states |F1> and |F2> is proposed. The protocol is implemented by the conditionally induced beam-splitter coupling which leads to the selective swapping between two photonic modes. Such coupling occurs in a quantum system prepared in the superposition of two ground states with only one of them being involved in the swapping. All the entangled states in the category, such as entangled pairs of coherent states or Fock states (N00N states), can be efficiently produced in the same way by this method.

Efficient Polarization Entanglement Distribution for W State Assisted by Frequency Degree of Freedom

We present an efficient faithful polarization entanglement distribution protocol for W state over an arbitrary noise channel, which use the frequency degree of freedom to carry the entanglement during the transmission. We describe the transmission of three-photon W state as an example, and then generalize this scheme to n-qubit W state situation. The remote parties can obtain maximally entangled W states on the polarization of photons, and the success probability is 100% in principle. As there was few entanglement purification for W state, our scheme is an efficient and practical method to share W state entanglement between distant parties, which will be useful in quantum communication. We also show that our scheme can be used to distribute arbitrary multi-particle entangled state.

CONCENTRATING ARBITRARY FOUR-PHOTON LESS-ENTANGLED CLUSTER STATE BY SINGLE PHOTONS

We present a protocol for concentrating an arbitrary four-photon entangled state into a maximally entangled state assisted with singled photons. The concentration protocol uses the linear optics and the cross-Kerr nonlinearity based on the post selection principle. Four parties called Alice, Bob, Charlie and Dan in different distant locations can obtain the cluster state from an arbitrary entangled four-photon state with a certain probability. Quantum non-demolition (QND) measurements are available in this protocol. Moreover, this scheme can be steady with a higher success possibility.

Generating arbitrary photon-number entangled states for continuous-variable quantum informatics

We propose two experimental schemes that can produce an arbitrary photon-number entangled state (PNES) in a finite dimension. This class of entangled states naturally includes non-Gaussian continuous-variable (CV) states that may provide some practical advantages over the Gaussian counterparts (two-mode squeezed states). We particularly compare the entanglement characteristics of the Gaussian and the non-Gaussian states in view of the degree of entanglement and the Einstein-Podolsky-Rosen correlation, and further discuss their applications to the CV teleportation and the nonlocality test. The experimental imperfection due to the on-off photodetectors with nonideal efficiency is also considered in our analysis to show the feasibility of our schemes within existing technologies.

15-μm band polarization entangled photon-pair source with variable Bell states

In this paper we report a polarization-entangled photon-pair source in a 1.5-μm band which can generate arbitrary entangled states including four maximum entangled states (Bell states) by using cascaded optical second nonlinearities (second-harmonic generation and the following spontaneous parametric down conversion) in a periodically poled LiNbO(3) (PPLN) ridge-waveguide device. Exchange among the Bell states was achieved by using an optical phase bias compensator (OPBC) in a Sagnac loop interferometer and a half-wave plate outside the loop for polarization conversion. Quantitative evaluation was made on the performance of the photon-pair source through the experiments of two-photon interferences, quantum state tomography, and test of violation of Bell inequality. We observed high visibilities of 96%, fidelities of 97%, and 2.71 of the S parameter in inequality of Clauser, Horne, Shimony, and Holt (CHSH). The experimental values, including peak coincidence counts in the two-photon interference (approximately 170 counts per second), remained almost unchanged in despite of the exchange among the Bell states. They were also in good agreement with the theoretical assumption from the mean number of the photon-pairs under the test (0.04 per pulse). More detailed experimental studies on the dependence of the mean number of the photon-pairs revealed that the quantum states were well understood as the Werner state.

Faithful teleportation with arbitrary pure or mixed resource states

We study faithful teleportation systematically with arbitrary entangled states as resources. The necessary conditions of mixed states to complete perfect teleportation are proved. Based on these results, the necessary and sufficient conditions of faithful teleportation of an unknown state |ϕ⟩ in with an entangled resource ρ in and are derived. It is shown that for ρ in , ρ must be a maximally entangled state, while for ρ in , ρ must be a pure maximally entangled state. Moreover, we show that the sender's measurements must be all projectors of maximally entangled pure states. The relations between the entanglement of the formation of the resource states and faithful teleportation are also discussed.

CONTINUOUS-VARIABLE QUANTUM TELEPORTATION OF MULTIPARTITE ENTANGLED COHERENT STATES

We investigate the problem of teleportation of tripartite entangled coherent state (ECS) using linear optical devices such as beam splitters, phase shifters, and two-mode number measurements. The scheme is based on the maximally four-partite ECS with bipartite maximal entanglement as the quantum channel to teleportation tripartite ECS. Our scheme is efficient in the sense that for mean number of photons equal to 2, the minimum of average fidelity (MAF) for teleportation an arbitrary tripartite entangled state is 1-2.3 × 10-7. We also generalize the tripartite scheme into multipartite case and calculate the MAF for the schemes in multipartite cases.

A Note on Teleportation of an Arbitrary Two-Particle State Without Bell-State Measurement in Cavity QED

We present a scheme using four two-level atoms and a bimodal cavity to get approximate conditional teleportation of an arbitrary entangled atomic state without using the Bell-state measurement.

Scheme for Implementing Teleporting an Arbitrary Tripartite Entangled State in Cavity QED

We propose to teleport an arbitrary tripartite entangled state in cavity QED. In this scheme, the five-qubit Brown state is chosen as the quantum channel. It has been shown that the teleportation protocol can be completed perfectly with two different measurement methods. In the future, our scheme might be realizable based on present experimental technology.

All Entangled States are Useful for Channel Discrimination

We prove that every entangled state is useful as a resource for the problem of minimum-error channel discrimination. More specifically, given a single copy of an arbitrary bipartite entangled state, it holds that there is an instance of a quantum channel discrimination task for which this state allows for a correct discrimination with strictly higher probability than every separable state.

An efficient scheme for generalized tripartite controlled teleportation of a two-quNit entangled state

A scheme for generalized controlled teleportation of an arbitrary two-quNit entangled state with N-dimensional partially Greenberger–Horne–Zeilinger (GHZ) state is proposed. A generalized Bell state measurement (BM) and a single-particle measurement in high dimensions are needed. According to the sender Alice's classical message, the receiver Charlie can restore the unknown two-quNit state with a certain probability by introducing an additional particle and performing a controlled-not (C-NOT) operation on his particles if she cooperates with the controller Bob. The total success probability and classical communication cost are calculated. We also generalize the scheme to the case where there are K controllers. It is shown that any one of the receivers can reconstruct the unknown state if he/she cooperates with all the controllers.

Teleportation of tripartite entangled coherent states

This paper proposes a feasible scheme for the quantum teleportation of tripartite entangled coherent states by using linear optical devices such as beam splitters, phase shifters and photo detectors. The scheme is based on the bipartite maximally entangled coherent state and the tripartite entangled coherent state with bipartite maximal entanglement as quantum channels. It shows that when the mean number of photons is equal to 2, the total minimum of the average fidelity for an arbitrary tripartite entangled state is 1 – 0.67 × 10−3.

TELEPORTATION OF AN ARBITRARY AND UNKNOWN JOSEPHSON CHARGE-QUBIT ENTANGLED STATE VIA A CLUSTER STATE

An experimentally feasible scheme for teleporting an arbitrary and unknown entangled state is proposed. In this paper, we use a cluster state as the quantum channel, and we do not need any joint Bell-state measurement (BSM). Our scheme is based on Josephson charge qubits, and the successful probability and fidelity of teleportation can both reach unity. Moreover, the current scheme can be realized within the current experimental technology.

IMPROVING THE TELEPORTATION OF TRIPARTITE ENTANGLED COHERENT STATES IN CONTINUOUS VARIABLE

We propose a feasible scheme for the quantum teleportation of tripartite entangled coherent state in terms of linear optical devices such as beam splitters, phase shifters and photo detectors. The scheme is based on the bipartite maximally entangled coherent state and the tripartite entangled coherent state with bipartite maximal entanglement as quantum channels. It shows that for an appreciable mean number of photons equal to 2, the total minimum of average fidelity for an arbitrary tripartite entangled state is 0.981684.

The Controlled Teleportation of an Arbitrary Two-Atom Entangled State in Driven Cavity QED

In this paper, we propose a scheme for the controlled teleportation of an arbitrary two-atom entangled state |φ〉12=a|gg〉12+b|ge〉12+c|eg〉12+d|ee〉12 in driven cavity QED. An arbitrary two-atom entangled state can be teleported perfectly with the help of the cooperation of the third side by constructing a three-atom GHZ entangled state as the controlled channel. This scheme does not involve apparent (or direct) Bell-state measurement and is insensitive to the cavity decay and the thermal field. The probability of the success in our scheme is 1.0.

PROBABILISTIC REMOTELY PREPARING AN ARBITRARY TWO-PARTICLE ENTANGLED STATE VIA POSITIVE OPERATOR-VALUED MEASURE

By means of the method of the positive operator-valued measure, two schemes to remotely prepare an arbitrary two-particle entangled state were presented. The first scheme uses a one-dimensional four-particle non-maximally entangled cluster state while the second one uses two partially entangled two-particle states as the quantum channel. For both schemes, if Alice performs two-particle projective measurements and Bob adopts positive operator-valued measure, the remote state preparation can be successfully realized with certain probability. The success probability of the remote state preparation and classical communication cost are calculated. It is shown that Bob can obtain the unknown state with probability 1/4 for maximally entangled state. However, for four kinds of special states, the success probability of preparation can be enhanced to unity.