20 research outputs found
Quantum stability of self-organized atomic insulator-like states in optical resonators
We investigate a paradigm example of cavity quantum electrodynamics with many
body systems: an ultracold atomic gas inside a pumped optical resonator. In
particular, we study the stability of atomic insulator-like states, confined by
the mechanical potential emerging from the cavity field spatial mode structure.
As in open space, when the optical potential is sufficiently deep, the atomic
gas is in the Mott-like state. Inside the cavity, however, the potential
depends on the atomic distribution, which determines the refractive index of
the medium, thus altering the intracavity field amplitude. We derive the
effective Bose-Hubbard model describing the physics of the system in one
dimension and study the crossover between the superfluid -- Mott insulator
quantum states. We determine the regions of parameters where the atomic
insulator states are stable, and predict the existence of overlapping stability
regions corresponding to competing insulator-like states. Bistable behavior,
controlled by the pump intensity, is encountered in the vicinity of the shifted
cavity resonance.Comment: 13 pages, 6 figures. Replaced with revised version. Accepted for
publication in New J. Phys., special issue "Quantum correlations in tailord
matter
Bandgaps in the propagation and scattering of surface water waves over cylindrical steps
Here we investigate the propagation and scattering of surface water waves by
arrays of bottom-mounted cylindrical steps. Both periodic and random
arrangements of the steps are considered. The wave transmission through the
arrays is computed using the multiple scattering method based upon a recently
derived formulation. For the periodic case, the results are compared to the
band structure calculation. We demonstrate that complete band gaps can be
obtained in such a system. Furthermore, we show that the randomization of the
location of the steps can significantly reduce the transmission of water waves.
Comparison with other systems is also discussed.Comment: 4 pages, 3 figure
Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics
The superposition principle is a very basic ingredient of quantum theory.
What may come as a surprise to many students, and even to many practitioners of
the quantum craft, is tha superposition has limitations imposed by certain
requirements of the theory. The discussion of such limitations arising from the
so-called superselection rules is the main purpose of this paper. Some of their
principal consequences are also discussed. The univalence, mass and particle
number superselection rules of non-relativistic quantum mechanics are also
derived using rather simple methods.Comment: 22 pages, no figure
Dilute gas of ultracold two-level atoms inside a cavity; generalized Dicke model
We consider a gas of ultracold two-level atoms confined in a cavity, taking
into account for atomic center-of-mass motion and cavity mode variations. We
use the generalized Dicke model, and analyze separately the cases of a
Gaussian, and a standing wave mode shape. Owing to the interplay between
external motional energies of the atoms and internal atomic and field energies,
the phase-diagrams exhibit novel features not encountered in the standard Dicke
model, such as the existence of first and second order phase transitions
between normal and superradiant phases. Due to the quantum description of
atomic motion, internal and external atomic degrees of freedom are highly
correlated leading to modified normal and superradiant phases.Comment: 10 pages, 7 figure
Older adults’ perspectives on HIV/AIDS prevention strategies for rural Kenya
Though prevention of HIV/AIDS is the mainstay of various responses to the epidemic,communication strategies used to motivate behavior change are challenged for lack of cultural appropriateness, hence the lack of success. Participatory communication that is culture-centered and culturally sensitive is emphasized in HIV/AIDS communication to engage affected communities in defining problems and finding appropriate solutions. This paper examines the views of older adults as key targets in HIV/AIDS prevention given the increasing number of elderly living with the disease and
their changing role as caregivers of those infected and affected by HIV. As cultural, social, political, and opinion leaders in rural communities, older adults are in a position to influence attitudes and
behaviors of their community members, but they have not been involved in the current HIV/AIDS prevention interventions. Several recommendations were made to inform the design and implementation of a culture-specific prevention program for rural Kenya