Narrow Results

We propose a scheme for entanglement swapping and entanglement concentration without joint measurement by using the two-photon Jaynes-Cummings model. In the scheme, we can generate a maximally entangled pair between two initially uncorrelated atoms or cavities. Furthermore, the entangled state between two cavities is found to be a photon entanglement of two photons in one cavity and zero in another cavity.

In this paper, we propose an entanglement concentration protocol for unknown tripartite W class states via the detection of photons which are leaked out from the cavities. In our scheme, the atom-cavity coupling strength is smaller than the cavity decay rate. Hence, the requirement on the quality factor of the cavities is greatly relaxed. The scheme is for nonpost-selection results and the fidelity of the scheme is not affected by the detection inefficiency and atomic decay. All the processes are within the current technologies.

We propose a protocol for realizing two entanglement concentration scheme with cross-Kerr nonlinearity and double cross-phase modulation method. In our protocols, two remote parties do not require the accurate information of the less entangled state and the double cross-phase modulation is introduced to overcome the errors caused by the imperfect Kerr interaction. By this way, a single-photon entanglement is concentrated, and a three-photon polarized GHZ state is also achieved. Furthermore this protocol can be scaled to multiphoton polarized GHZ state concentration and the giant Kerr media is not needed, which makes our protocols more feasible in experiment.

Multi-particle cluster states play a significant role in quantum information processing. However, due to the inevitable interaction with the environment in the transmission process, the fidelity of entanglement decreases. To distill the perfect cluster states, we present two schemes for arbitrary six-particle cluster states. POVM local unitary operators that are obtained by solving the equation according to the properties of cluster states are used in the first protocol. The second protocol is based on cross-Kerr nonlinearity which is exploited to check parity between original qubit with ancillary single qubit and it can achieve a higher probability of success through iteration. Furthermore, we can generalize the first method to concentrate entanglement on even number of particles. Our protocol will be useful in practical applications.

We propose two schemes via adiabatic evolution of dark eigenstates in an ion trap system. One is an entanglement generation of multi-ion cluster states, the other is entanglement concentration via entanglement swapping. Our schemes are robust against moderate fluctuations of experimental parameters since we utilize the adiabatic passage in the main procedure. The current idea can be generalized to other systems.

An entanglement concentration protocol in photonic collective-rotating decoherence-free subspace (CRDFS) is proposed. To accomplish the scheme, two methods to construct parity measurement devices in CRDFS are presented by exploiting the cross-Kerr nonlinearity, through which partially entangled states are converted to maximally entangled states. The performance of the protocol can be improved by iteration method. Fidelity in consideration of dissipation is discussed, which demonstrates good robustness. In contrast to the conventional protocols, the present one has distinctive feature since it can not only get maximally entangled state from less entangled state, but also maintain the maximal entanglement in collective-rotating noise environment.

Two schemes for controlled dense coding with a extended GHZ state are investigated. In these protocols, the supervisor (Cliff) can control the average amount of information transmitted from the sender (Alice) to the receiver (Bob) only by adjusting his local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.