3,007 research outputs found
Non-equilibrium entanglement in a driven Dicke model
We study the entanglement dynamics in the externally-driven single-mode Dicke
model in the thermodynamic limit, when the field is in resonance with the
atoms. We compute the correlations in the atoms-field ground state by means of
the density operator that represents the pure state of the universe and the
reduced density operator for the atoms, which results from taking the partial
trace over the field coordinates. As a measure of bipartite entanglement, we
calculate the linear entropy, from which we analyze the entanglement dynamics.
In particular, we found a strong relation between the stability of the
dynamical parameters and the reported entanglement.Comment: Contribution to the SLAFES XIX. This version to appear in J. Phys.:
Conference Serie
El malestar de las corridas en la España actual (y la relación del mismo con el encaje de lo español en Europa)
La corrida de toros en la España actual –enmarcada en un contexto europeo- ha logrado tener una enorme importancia en los sentidos politicos, culturales, y simbĂłlicos. Este artĂculo comienza por examinar reacciones a la cornada mortal del torero VĂctor Barrio, quien era para unos un hĂ©roe, para otros un torturador de animales. El artĂculo sigue con un análisis de tres sectores de ciudadanos en protesta a la corrida: (1) nacionalistas catalanes, (2) españoles identificados con la nueva Europa, y (3) animalistas. El artĂculo concluye por explicar las posturas hacia otros espectáculos en la PenĂnsula IbĂ©rica que incluyen toros, especialmente el correbous de Catalunya.The bullfight in today’s Spain has attained enormous political, cultural, and symbolic salience. This article examines media reactions to the death in the bullring of torero VĂctor Barrio, to some citizens a hero, but to others an animal abuser. The article goes on to analyze opposition to bullfighting from three sectors of Spanish society: (1) Catalan nationalists, (2) Spaniards who identify with the new Europe, and (3) animal rights advocates. It concludes with public attitudes towards other bull-related public spectacles, especially the Catalan correbous
Truncation method for Green's functions in time-dependent fields
We investigate the influence of a time dependent, homogeneous electric field
on scattering properties of non-interacting electrons in an arbitrary static
potential. We develop a method to calculate the (Keldysh) Green's function in
two complementary approaches. Starting from a plane wave basis, a formally
exact solution is given in terms of the inverse of a matrix containing
infinitely many 'photoblocks' which can be evaluated approximately by
truncation. In the exact eigenstate basis of the scattering potential, we
obtain a version of the Floquet state theory in the Green's functions language.
The formalism is checked for cases such as a simple model of a double barrier
in a strong electric field. Furthermore, an exact relation between the
inelastic scattering rate due to the microwave and the AC conductivity of the
system is derived which in particular holds near or at a metal-insulator
transition in disordered systems.Comment: to appear in Phys. Rev. B., 21 pages, 3 figures (ps-files
Feedback Control of Quantum Transport
The current through nanostructures like quantum dots can be stabilized by a
feedback loop that continuously adjusts system parameters as a function of the
number of tunnelled particles . At large times, the feedback loop freezes
the fluctuations of which leads to highly accurate, continuous single
particle transfers. For the simplest case of feedback acting simultaneously on
all system parameters, we show how to reconstruct the original full counting
statistics from the frozen distribution.Comment: 4 pages, 2 figure
Adiabatic steering and determination of dephasing rates in double dot qubits
We propose a scheme to prepare arbitrary superpositions of quantum states in
double quantum--dots irradiated by coherent microwave pulses. Solving the
equations of motion for the dot density matrix, we find that dephasing rates
for such superpositions can be quantitatively infered from additional electron
current pulses that appear due to a controllable breakdown of coherent
population trapping in the dots.Comment: 5 pages, 4 figures. To appear in Phys. Rev.
Dicke Effect in the Tunnel Current through two Double Quantum Dots
We calculate the stationary current through two double quantum dots which are
interacting via a common phonon environment. Numerical and analytical solutions
of a master equation in the stationary limit show that the current can be
increased as well as decreased due to a dissipation mediated interaction. This
effect is closely related to collective, spontaneous emission of phonons (Dicke
super- and subradiance effect), and the generation of a `cross-coherence' with
entanglement of charges in singlet or triplet states between the dots.
Furthermore, we discuss an inelastic `current switch' mechanism by which one
double dot controls the current of the other.Comment: 12 pages, 6 figures, to appear in Phys. Rev.
Equation of motion method for Full Counting Statistics: Steady state superradiance
For the multi-mode Dicke model in a transport setting that exhibits
collective boson transmissions, we construct the equation of motion for the
cumulant generating function. Approximating the exact system of equations at
the level of cumulant generating function and system operators at lowest order,
allows us to recover master equation results of the Full Counting Statistics
for certain parameter regimes at very low cost of computation. The
thermodynamic limit, that is not accessible with the master equation approach,
can be derived analytically for different approximations.Comment: 7 pages, 3 figures, revised version, accepted by PR
Two-Particle Dark State in the Transport through a Triple Quantum Dot
We study transport through a triple quantum dot in a triangular geometry with
applied bias such that both singly- and doubly- charged states participate. We
describe the formation of electronic dark states -- coherent superpositions
that block current flow -- in the system, and focus on the formation of a
two-electron dark state. We discuss the conditions under which such a state
forms and describe the signatures that it leaves in transport properties such
as the differential conductance and shotnoise.Comment: (9 pages, 7 figures), we now consider two different sets of charging
energie
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