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

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

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.