3,585 research outputs found
Generation of Superposition States and Charge-Qubit Relaxation Probing in a Circuit
We demonstrate how a superposition of coherent states can be generated for a
microwave field inside a coplanar transmission line coupled to a single
superconducting charge qubit, with the addition of a single classical magnetic
pulse for chirping of the qubit transition frequency. We show how the qubit
dephasing induces decoherence on the field superposition state, and how it can
be probed by the qubit charge detection. The character of the charge qubit
relaxation process itself is imprinted in the field state decoherence profile.Comment: 6 pages, 4 figure
Generalized Chaplygin gas with and the cosmological model
The generalized Chaplygin gas model is characterized by the equation of state
. It is generally stated that the case is equivalent to a model with cosmological constant and dust (). In this work we show that, if this is true for the background equations,
this is not true for the perturbation equations. Hence, the mass spectrum
predicted for both models may differ.Comment: Latex file, 4 pages, 2 figures in eps forma
Vortex-Antivortex Lattice in Ultra-Cold Fermi Gases
We discuss ultra-cold Fermi gases in two dimensions, which could be realized
in a strongly confining one-dimensional optical lattice. We obtain the
temperature versus effective interaction phase diagram for an s-wave superfluid
and show that, below a certain critical temperature T_c, spontaneous
vortex-antivortex pairs appear for all coupling strengths. In addition, we show
that the evolution from weak to strong coupling is smooth, and that the system
forms a square vortex-antivortex lattice at a lower critical temperature T_M.Comment: Submitted to Physical Review Letter
Lattice Simulation of Nuclear Multifragmentation
Motivated by the decade-long debate over the issue of criticality supposedly
observed in nuclear multifragmentation, we propose a dynamical lattice model to
simulate the phenomenon. Its Ising Hamiltonian mimics a short range attractive
interaction which competes with a thermal-like dissipative process. The results
here presented, generated through an event-by-event analysis, are in agreement
with both experiment and those produced by a percolative (non-dynamical) model.Comment: 8 pages, 3 figure
Superconducting and normal-state interlayer-exchange-coupling in LaSrMnO-YBaCuO_{0.67}_{0.33}{3}$ epitaxial trilayers
The issue of interlayer exchange coupling in magnetic multilayers with
superconducting (SC) spacer is addressed in LaSrMnO
(LSMO) - YBaCuO (YBCO) - LaSrMnO
(LSMO) epitaxial trilayers through resistivity, ac-susceptibility and
magnetization measurements. The ferromagnetic (FM) LSMO layers possessing
in-plane magnetization suppress the critical temperature (T of the
c-axis oriented YBCO thin film spacer. The superconducting order, however,
survives even in very thin layers (thickness d 50 {\AA}, 4
unit cells) at T 25 K. A predominantly antiferromagnetic (AF) exchange
coupling between the moments of the LSMO layers at fields 200 Oe is seen in
the normal as well as the superconducting states of the YBCO spacer. The
exchange energy J ( 0.08 erg/cm at 150 K for d = 75
{\AA}) grows on cooling down to T, followed by truncation of this growth
on entering the superconducting state. The coupling energy J at a fixed
temperature drops exponentially with the thickness of the YBCO layer. The
temperature and d dependencies of this primarily non-oscillatory J
are consistent with the coupling theories for systems in which transport is
controlled by tunneling. The truncation of the monotonic T dependence of
J below T suggests inhibition of single electron tunneling across
the CuO planes as the in-plane gap parameter acquires a non-zero value.Comment: Accepted for publication in Phys. Rev.
Complex networks generated by the Penna bit-string model: emergence of small-world and assortative mixing
The Penna bit-string model successfully encompasses many phenomena of population evolution, including inheritance, mutation, evolution, and aging. If we consider social interactions among individuals in the Penna model, the population will form a complex network. In this paper, we first modify the Verhulst factor to control only the birth rate, and introduce activity-based preferential reproduction of offspring in the Penna model. The social interactions among individuals are generated by both inheritance and activity-based preferential increase. Then we study the properties of the complex network generated by the modified Penna model. We find that the resulting complex network has a small-world effect and the assortative mixing property
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