Current and entanglement in a Bose-Hubbard lattice

We study the generation of entanglement for interacting cold atoms in an optical lattice. The entanglement is generated by managing the interaction between two distinct atomic species. It is found that the current of one of the species can be used as a good indicator of entanglement generation. The thermalization process between the species is also shown to be closely related to the evolution of the current.Comment: 10 pages, 5 figure

Hispanics and the Current Economic Downturn: Will the Receding Tide Sink Hispanics?

Explores the progress made by Hispanics during the economic boom of the 1990s, and examines the potential impact of the 2001/2002 economic slowdown on Hispanic workers and families

Quantum theory of a two-mode open-cavity laser

We develop the quantum theory of an open-cavity laser assuming that only two modes compete for gain. We show that the modes interact to build up a collective mode that becomes the lasing mode when pumping exceeds a threshold. This collective mode exhibits all the features of a typical laser mode, whereas its precise behavior depends explicitly on the openness of the cavity. We approach the problem by using the density-matrix formalism and derive the master equation for the light field. Our results are of particular interest in the context random laser systems.Comment: 20 pages, 5 figure

Relaxation dynamics of an exactly solvable electron-phonon model

We address the question whether observables of an exactly solvable model of electrons coupled to (optical) phonons relax into large time stationary state values and investigate if the asymptotic expectation values can be computed using a stationary density matrix. Two initial nonequilibrium situations are considered. A sudden quench of the electron-phonon coupling, starting from the noninteracting canonical equilibrium at temperature T in the electron as well as in the phonon subsystems, leads to a rather simple dynamics. A richer time evolution emerges if the initial state is taken as the product of the phonon vacuum and the filled Fermi sea supplemented by a highly excited additional electron. Our model has a natural set of constants of motion, with as many elements as degrees of freedom. In accordance with earlier studies of such type of models we find that expectation values which become stationary can be described by the density matrix of a generalized Gibbs ensemble which differs from that of a canonical ensemble. For the model at hand it appears to be evident that the eigenmode occupancy operators should be used in the construction of the stationary density matrix.Comment: 15 pages, 11 figures, published versio

Total Quantum Zeno Effect beyond Zeno Time

In this work we show that is possible to obtain Total Quantum Zeno Effect in an unstable systems for times larger than the correlation time of the bath. The effect is observed for some particular systems in which one can chose appropriate observables which frequent measurements freeze the system into the initial state. For a two level system in a squeezed bath one can show that there are two bath dependent observables displaying Total Zeno Effect when the system is initialized in some particular states. We show also that these states are intelligent states of two conjugate observables associated to the electromagnetic fluctuations of the bath.Comment: 6 pages, 3 figures, Contributed to Quantum Optics III, Pucon, Chile, November 200

Decoherence Free Subspace and entanglement by interaction with a common squeezed bath

In this work we find explicitly the decoherence free subspace (DFS) for a two two-level system in a common squeezed vacuum bath. We also find an orthogonal basis for the DFS composed of a symmetrical and an antisymmetrical (under particle permutation) entangled state. For any initial symmetrical state, the master equation has one stationary state which is the symmetrical entangled decoherence free state. In this way, one can generate entanglement via common squeezed bath of the two systems. If the initial state does not have a definite parity, the stationary state depends strongly on the initial conditions of the system and it has a statistical mixture of states which belong to the DFS. We also study the effect of the coupling between the two-level systems on the DFS.Comment: 4 pages, 1 figur

Cooling of Nanomechanical Resonator Based on Periodical Coupling to Cooper Pair Box

We propose and study an active cooling mechanism for the nanomechanical resonator (NAMR) based on periodical coupling to a Cooper pair box (CPB), which is implemented by a designed series of magnetic flux pluses threading through the CPB. When the initial phonon number of the NAMR is not too large, this cooling protocol is efficient in decreasing the phonon number by two to three orders of magnitude. Our proposal is theoretically universal in cooling various boson systems of single mode. It can be specifically generalized to prepare the nonclassical state of the NAMR.Comment: 5pages,3figure

Total Quantum Zeno effect and Intelligent States for a two level system in a squeezed bath

In this work we show that by frequent measurements of adequately chosen observables, a complete suppression of the decay in an exponentially decaying two level system interacting with a squeezed bath is obtained. The observables for which the effect is observed depend on the the squeezing parameters of the bath. The initial states which display Total Zeno Effect are intelligent states of two conjugate observables associated to the electromagnetic fluctuations of the bath.Comment: 5 pages, 3 figure

The Simple Economics of Funded and Unfunded Pension Systems

Most state pension schemes are financed on a pay-as-you-go (PAYG) basis, which means that taxes on the young are used to pay for the pensions of the retired generation. With private pensions, however, a fund of assets is built up and invested. Some countries such as Chile and Australia have moved to a mandatory funded pension system and the Conservatives in the U.K. have proposed to do the same with their Basic Pension Plus proposal. Other countries such as the U.S. and Sweden have built up a funded reserve to help ease the payment of pensions when the ‘baby boom’ generation retires. This article reviews the economic theories of funded and unfunded pension systems and examines the advantages and disadvantages of each type of system; these theories help to explain the current interest in funded systems as well as the difficulties associated with the transition towards them

Simultaneous cooling of an artificial atom and its neighboring quantum system

We propose an approach for cooling both an artificial atom (e.g., a flux qubit) and its neighboring quantum system, the latter modeled by either a quantum two-level system or a quantum resonator. The flux qubit is cooled by manipulating its states, following an inverse process of state population inversion, and then the qubit is switched on to resonantly interact with the neighboring quantum system. By repeating these steps, the two subsystems can be simultaneously cooled. Our results show that this cooling is robust and effective, irrespective of the chosen quantum systems connected to the qubit.Comment: 5 pages, 3 figure