369 research outputs found
Berry Phase Quantum Thermometer
We show how Berry phase can be used to construct an ultra-high precision
quantum thermometer. An important advantage of our scheme is that there is no
need for the thermometer to acquire thermal equilibrium with the sample. This
reduces measurement times and avoids precision limitations.Comment: Updated to published version. I. Fuentes previously published as I.
Fuentes-Guridi and I. Fuentes-Schulle
No-Boundary Theta-Sectors in Spatially Flat Quantum Cosmology
Gravitational theta-sectors are investigated in spatially locally homogeneous
cosmological models with flat closed spatial surfaces in 2+1 and 3+1 spacetime
dimensions. The metric ansatz is kept in its most general form compatible with
Hamiltonian minisuperspace dynamics. Nontrivial theta-sectors admitting a
semiclassical no-boundary wave function are shown to exist only in 3+1
dimensions, and there only for two spatial topologies. In both cases the
spatial surface is nonorientable and the nontrivial no-boundary theta-sector
unique. In 2+1 dimensions the nonexistence of nontrivial no-boundary
theta-sectors is shown to be of topological origin and thus to transcend both
the semiclassical approximation and the minisuperspace ansatz. Relation to the
necessary condition given by Hartle and Witt for the existence of no-boundary
theta-states is discussed.Comment: 30 p
Topological geon black holes in Einstein-Yang-Mills theory
We construct topological geon quotients of two families of
Einstein-Yang-Mills black holes. For Kuenzle's static, spherically symmetric
SU(n) black holes with n>2, a geon quotient exists but generically requires
promoting charge conjugation into a gauge symmetry. For Kleihaus and Kunz's
static, axially symmetric SU(2) black holes a geon quotient exists without
gauging charge conjugation, and the parity of the gauge field winding number
determines whether the geon gauge bundle is trivial. The geon's gauge bundle
structure is expected to have an imprint in the Hawking-Unruh effect for
quantum fields that couple to the background gauge field.Comment: 27 pages. v3: Presentation expanded. Minor corrections and addition
Singularity avoidance by collapsing shells in quantum gravity
We discuss a model describing exactly a thin spherically symmetric shell of
matter with zero rest mass. We derive the reduced formulation of this system in
which the variables are embeddings, their conjugate momenta, and Dirac
observables. A non-perturbative quantum theory of this model is then
constructed, leading to a unitary dynamics. As a consequence of unitarity, the
classical singularity is fully avoided in the quantum theory.Comment: 5 pages, 1 figure, received honorable mention in the 2001 essay
competititon, to appear in Int. J. Mod. Phys.
On Quantum Nature of Black-Hole Spacetime: A Possible New Source of Intense Radiation
Atoms and the planets acquire their stability from the quantum mechanical
incompatibility of the position and momentum measurements. This incompatibility
is expressed by the fundamental commutator [x, p_x]=i hbar, or equivalently,
via the Heisenberg's uncertainty principle Delta x Delta p_x sim hbar. A
further stability-related phenomenon where the quantum realm plays a dramatic
role is the collapse of certain stars into white dwarfs and neutron stars.
Here, an intervention of the Pauli exclusion principle, via the fermionic
degenerate pressure, stops the gravitational collapse. However, by the
neutron-star stage the standard quantum realm runs dry. One is left with the
problematic collapse of a black hole. This essay is devoted to a concrete
argument on why the black-hole spacetime itself should exhibit a quantum
nature. The proposed quantum aspect of spacetime is shown to prevent the
general-relativistic dictated problematic collapse. The quantum nature of
black-hole spacetime is deciphered from a recent result on the universal
equal-area spacing [=lambda_P^2 4 ln(3)] for black holes. In one interpretation
of the emergent picture, an astrophysical black hole can fluctuate to
sqrt{pi/ln(3)} approx 1.7 times its classical size, and thus allow radiation
and matter to escape to the outside observers. These fluctuations I conjecture
provide a new source, perhaps beyond Hawking radiation, of intense radiation
from astrophysical black holes and may be the primary source of observed
radiation from those galactic cores what carry black hole(s). The presented
interpretation may be used as a criterion to choose black holes from black hole
candidates.Comment: This essay received an "honorable mention" in the 1999 Essay
Competition of the Gravity Research Foundation - Ed. Int. J. Mod. Phys. D
(1999, in press). For Joseph Knech
- …