Einstein-Podolsky-Rosen Entanglement Research Articles

Scheme for Realizing Deterministic Entanglement Concentration with Atoms Via Cavity QED

A scheme for concentrating entanglement in two partially entangled Einstein-Podolsky-Rosen (EPR) pairs using repetitious resonant interactions of the atoms with a single-mode cavity field is proposed. A maximally entangled EPR pair can be deterministically extracted with the success probability of 1.0. In the scheme, the two logical states of a qubit are represented by the two lowest levels of an atom while a higher-energy intermediate level is used to facilitate the realization of the unitary operations, and all the operations required to realize deterministic entanglement concentration can be implemented in a reasonable amount of time before decoherence sets in. The scheme might be experimentally realizable with presently available cavity QED techniques and gives a realistic means to realize entanglement concentration deterministically.

Tunable delay of Einstein–Podolsky–Rosen entanglement

Entangled systems display correlations that are stronger than can be obtained classically. This makes entanglement an essential resource for a number of applications, such as quantum information processing, quantum computing and quantum communications. The ability to control the transfer of entanglement between different locations will play a key role in these quantum protocols and enable quantum networks. Such a transfer requires a system that can delay quantum correlations without significant degradation, effectively acting as a short-term quantum memory. An important benchmark for such systems is the ability to delay Einstein-Podolsky-Rosen (EPR) levels of entanglement and to be able to tune the delay. EPR entanglement is the basis for a number of quantum protocols, allowing the remote inference of the properties of one system (to better than its standard quantum limit) through measurements on the other correlated system. Here we show that a four-wave mixing process based on a double-lambda scheme in hot (85)Rb vapour allows us to obtain an optically tunable delay for EPR entangled beams of light. A significant maximum delay, of the order of the width of the cross-correlation function, is achieved. The four-wave mixing also preserves the quantum spatial correlations of the entangled beams. We take advantage of this property to delay entangled images, making this the first step towards a quantum memory for images.

Multi-mode Einstein–Podolsky–Rosen Entangled State Representation and Its Applications

Our primary purpose of this work is to explicitly construct the general multipartite Einstein–Podolsky–Rosen (EPR) entangled state in multi-mode Fock space for a system with different masses of particles, which makes up a new quantum mechanical representation owing to completeness relation and orthogonal property. Its entanglement can be seen more clearly by analyzing its standard Schmidt decomposition. In addition, some applications of the multipartite entanglement are proposed including deriving the generalized Wigner operator and squeezing operator.

Teleportation of an arbitrary unknown N-qubit entangled state under the controlling of M controllers

A new quantum protocol to teleport an arbitrary unknown N-qubit entangled state from a sender to a fixed receiver under M controllers(M < N) is proposed. The quantum resources required are M non-maximally entangled Greenberger-Horne-Zeilinger (GHZ) state and N-M non-maximally entangled Einstein-Podolsky-Rosen (EPR) pairs. The sender performs N generalized Bell-state measurements on the 2N particles. Controllers take M single-particle measurement along x-axis, and the receiver needs to introduce one auxiliary two-level particle to extract quantum information probabilistically with the fidelity unit if controllers cooperate with it.

Quantum secure communication using continuous variable Einstein-Podolsky-Rosen correlations

A quantum secure communication protocol using correlations of continuous variable Einstein-Podolsky-Rosen (EPR) pairs is proposed. The proposed protocol may implement both quantum key distribution and quantum message encryption by using a nondegenerate optical parametric amplifier (NOPA). The general Gaussian-cloner attack strategy is investigated in detail by employing Shannon information theory. Results show that the proposed scheme is secure, which is guaranteed physically by the correlations of the continuous variable EPR entanglement pairs generated by the NOPA.

Quantum teleportation of single-mode thermal state of light field

The quantum teleportation of a single-mode thermal state of a light field is discussed using the projection synthesis technique in the Schrodinger picture. The statistical distance (SD) between the teleported input and output states is introduced to evaluate the efficiency of single-mode thermal state teleportation. For a given system and available entanglement, both the SD and classical boundary depend on the mean photon numbers of the teleported thermal light field. The dependences of the SD on the normalized classical gain, EPR (Einstein–Podolsky–Rosen) entanglement and mean photon numbers of the thermal field are calculated.

EPR Entangled States for Bipartite Kinematics and New Bosonic Representation of SU(2) Algebra**The project supported by National Natural Science Foundation of China under Grant No. 10175057 and the President Foundation of the Chinese Academy of Sciences

We find that the Einstein-Podolsky-Rosen (EPR) entangled state representation describing bipartite kinematics is closely related to a new Bose operator realization of SU(2) Lie algebra. By virtue of the new realization some Hamiltonian eigenfunction equation can be directly converted to the generalized confluent equation in the EPR entangled state representation and its solution is obtainable. This thus provides a new approach for studying dynamics of angular momentum systems.

Generation of continuous variable Einstein-Podolsky-Rosen entanglement via the Kerr nonlinearity in an optical fiber.

We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in the fiber is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures is measured to be 4.0+/-0.2 (4.0+/-0.4) dB below the quantum noise limit. The sum criterion for these squeezing variances 0.80+/-0.03<2 verifies the nonseparability of the state. The product of the inferred uncertainties for one beam (0.64+/-0.08) is well below the EPR limit of unity.

Einstein-Podolsky-Rosen entanglement for self-interacting complex scalar fields

We demonstrate the Einstein-Podolsky-Rosen (EPR) correlations in the Gaussian trial wavefunctional widely used in the Schrodinger representation of the self-interacting complex scalar fields (CSF). This demonstration is based on the explicit eigenstates ||ξ, which possess the precise EPR entanglement and constitute a complete and orthonormal representation, of CSF and † in the Fock space. To show the entanglement of the Gaussian trial wavefunctional, we evaluate in the ξ||-representation its `entangled' Wigner functional resembling the Wigner function of the two-mode squeezed vacuum state, whose quantum entanglement is well known.

Demonstration of Einstein–Podolsky–Rosen entanglement for an electron in a uniform magnetic field

The precise Einstein–Podolsky–Rosen entanglement for an electron in a uniform magnetic field is demonstrated. Specifically, the electron possesses sharp correlations in the common eigenstates ξ B ( η B ) of electron's x- and y-coordinates (the canonical momenta p x and p y ), a novel fact unnoticed before. The Schmidt decomposition of ξ B clearly shows the Einstein–Podolsky–Rosen correlations directly related to their original argument.