In this paper, decoherence in a system consisting of two Bose-Einstein condensates is investigated analytically. It is indicated that decoherence can be controlled through manipulating the interaction between the system and environment. The influence of the decoherence on quantum coherent atomic tunneling (AT) between two condensates with arbitrary initial states is studied in detail. Analytic expressions of the population difference (PD) and the AT current between two condensates are found. It is shown that the decoherence leads to the decay of the PD and the suppression of the AT current.

We present a nonlinear decoherence model which models decoherence effect caused by various decohereing sources in a quantum system through a nonlinear coupling between the system and its environment, and apply it to investigating decoherence in nonclassical motional states of a single trapped ion. We obtain an exactly analytic solution of the model and find very good agreement with experimental results for the population decay rate of a single trapped ion observed in the NIST experiments by coworkers (D. M. Meekhof, et al., Phys. Rev. Lett. 76, 1796 (1996)). PACS numbers: 32.80. Pj, 42.50.Lc, 03.65.Bz, 05.45.+b In recent years, much progress has been made in preparation, manipulation, and measurement of quantum states of the center-of-mass vibrational motion of a single trapped ion experimentally [1][2][3][4][5][6][7][8] and theoretically [9][10][11][12][13][14][15][16], which are not only of fundamental physical interest but also of practical use for sensitive detection of weak signals [17] and quantum computation in an ion trap [3,9]. In particular, the NIST group [4] has experimentally created and observed nonclassical motional states of a single trapped ion. In the NIST experiments [4], an anti Jaynes-Cummings model (JCM) interaction between the internal and motional states of a trapped ion is realized through stimulated Raman transitions, which couple internal states of the trapped ion to its motional states, when the Lamb-Dicke limit is satisfied and the driving laser fields are tuned to the first blue sideband. Detection of motional states is carried out by observing the evolution characteristics of quantum dynamics of internal levels of the trapped ion under influence of the anti JCM-typed interaction. The NIST experiments revealed the fact that the population of the low atomic state (P ↓ ) evolves according to the following phenomenological expressionwhere p n is the initial probability distribution of motional states of the trapped ion in the Fock representation, g is a coupling constant between the atomic internal and motional states, γ n is a decay rate. The experimentally observed decay rate is of the following formwhere the observed value of ν is ν . = 0.7. A question that naturally arises is: how to explain the above experimentally observed decay rate? It is generally accepted that the appearance of the decay factor γ n in the evolution of internal states is a consequence of decoherence. It is of practical significance to well understand decoherence for preparation of nonclassical states and quantum computation in ion traps. There are various sources of decoherence [1], such as ion vibrational decoherence, ion internal-state decoherence, decoherence caused by non-ideal external fields, and so on. Recently, Schneider and Milburn [18] have investigated decoherence due to laser intensity and phase fluctuations and obtained the power ν in Eq.(2) being ν . = 0.5 instead of the experimentally observed value 0.7. More recently, Murao and Knight [19], using master equation method, have studied decohe...

The adsorption of flexible polyelectrolyte (PE) with the smeared charge distribution onto an oppositely charged sphere immersed in a PE solution is studied numerically with the continuum self-consistent field theory. The power law scaling relationships between the boundary layer thickness and the surface charge density and the charge fraction of PE chains revealed in the study are in good agreement with the existing analytical result. The curvature effect on the degree of charge compensation of the total amount of charges on the adsorbed PE chains over the surface charges is examined, and a clear understanding of it based on the dependences of the degree of charge compensation on the surface charge density and the charge fraction of PE chains is established.

We introduce entanglement measures to describe entanglement in a three-particle system and apply it to studying broadcasting of entanglement in the three-particle Greenberger-Horne-Zeilinger (GHZ) state. The results show that the entanglement of the three-qubit GHZstate can be partially broadcasted with the help oflocal or non-local copying processes. It is found that non-local cloning is much more efficient than local cloning for the broadcasting of entanglement.