12,189 research outputs found
Oscillatons revisited
In this paper, we study some interesting properties of a spherically
symmetric oscillating soliton star made of a real time-dependent scalar field
which is called an oscillaton. The known final configuration of an oscillaton
consists of a stationary stage in which the scalar field and the metric
coefficients oscillate in time if the scalar potential is quadratic. The
differential equations that arise in the simplest approximation, that of
coherent scalar oscillations, are presented for a quadratic scalar potential.
This allows us to take a closer look at the interesting properties of these
oscillating objects. The leading terms of the solutions considering a quartic
and a cosh scalar potentials are worked in the so called stationary limit
procedure. This procedure reveals the form in which oscillatons and boson stars
may be related and useful information about oscillatons is obtained from the
known results of boson stars. Oscillatons could compete with boson stars as
interesting astrophysical objects, since they would be predicted by scalar
field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version
published in Classical and Quantum Gravit
On the Space Time of a Galaxy
We present an exact solution of the averaged Einstein's field equations in
the presence of two real scalar fields and a component of dust with spherical
symmetry. We suggest that the space-time found provides the characteristics
required by a galactic model that could explain the supermassive central object
and the dark matter halo at once, since one of the fields constitutes a central
oscillaton surrounded by the dust and the other scalar field distributes far
from the coordinate center and can be interpreted as a halo. We show the
behavior of the rotation curves all along the background. Thus, the solution
could be a first approximation of a ``long exposition photograph'' of a galaxy.Comment: 8 pages REVTeX, 11 eps figure
Entangled coherent states and squeezing in N trapped ions
We consider a resonant bichromatic excitation of N trapped ions that
generates displacement and squeezing in their collective motion conditioned to
their ionic internal state, producing eventually Scrhodinger cat states and
entangled squeezing. Furthermore, we study the case of tetrachromatic
illumination or producing the so called entangled coherent states in two
motional normal modes.Comment: 4 Revtex pages, no figures. To appear in Proceedings of "Mysteries,
Puzzles and Paradoxes in Quantum Mechanics", Garda Lake, Italy (2001
Reliable teleportation in trapped ions
We study a method for the implementation of a reliable teleportation protocol
(theoretically, 100% of success) of internal states in trapped ions. The
generation of the quantum channel (any of four Bell states) may be done
respecting technical limitations on individual addressing and without claiming
the Lamb-Dicke regime. An adequate Bell analyzer, that transforms unitarily the
Bell basis into a completely disentangled one, is considered. Probable sources
of error and fidelity estimations of the teleportation process are studied.
Finally, we discuss experimental issues, proposing a scenario in which the
present scheme could be implemented.Comment: 8 Latex pages with five (ps,eps) figures included (EPJ style also
included). Accepted for publication in European Physical Journal
Decoherence, pointer engineering and quantum state protection
We present a proposal for protecting states against decoherence, based on the
engineering of pointer states. We apply this procedure to the vibrational
motion of a trapped ion, and show how to protect qubits, squeezed states,
approximate phase eigenstates and superpositions of coherent states.Comment: 1 figur
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