12 research outputs found
Recoherence in the entanglement dynamics and classical orbits in the N-atom Jaynes-Cummings model
The rise in linear entropy of a subsystem in the N-atom Jaynes-Cummings model
is shown to be strongly influenced by the shape of the classical orbits of the
underlying classical phase space: we find a one-to-one correspondence between
maxima (minima) of the linear entropy and maxima (minima) of the expectation
value of atomic excitation J_z. Since the expectation value of this operator
can be viewed as related to the orbit radius in the classical phase space
projection associated to the atomic degree of freedom, the proximity of the
quantum wave packet to this atomic phase space borderline produces a maximum
rate of entanglement. The consequence of this fact for initial conditions
centered at periodic orbits in regular regions is a clear periodic recoherence.
For chaotic situations the same phenomenon (proximity of the atomic phase space
borderline) is in general responsible for oscillations in the entanglement
properties.Comment: 15 pages (text), 6 figures; to be published in Physical Review
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
Fano resonances in the conductance of quantum dots with mixed dynamics
We study the conductance fluctuations of an open quantum dot with underlying mixed dynamics. In addition to smooth conductance fluctuations, typical of chaotic quantum dots, we observe the occurrence of many sharp conductance peaks. Those are associated with localized states in the quantum dot and display a variety of Fano shape resonances. We show that the Fano q parameter in the presence of time-reversal symmetry is, in general, complex. We discuss the origin of the different Fano parameters and present a numerical study to support our theory.771
PARTICLE-SPIN COUPLING IN A CHAOTIC SYSTEM - LOCALIZATION-DELOCALIZATION IN THE HUSIMI DISTRIBUTIONS
The wave functions of the Dicke Hamiltonian, describing a spin coupled to a bosonic mode, are studied via Husimi distributions. A classical analogue of this system is also obtained. For several energy ranges studied, the Husimi distribution of the wave functions show the scar of simple periodic orbits when projected into the boson phase space. Surprisingly, these same distributions, when projected into the spin phase space, are spread through large regions. An explanation of this fact is given in terms of semiclassical theory and border effects associated with nonsemiclassical behaviour.15212513