3,306 research outputs found
Probing quantum-mechanical level repulsion in disordered systems by means of time-resolved selectively-excited resonance fluorescence
We argue that the time-resolved spectrum of selectively-excited resonance
fluorescence at low temperature provides a tool for probing the
quantum-mechanical level repulsion in the Lifshits tail of the electronic
density of states in a wide variety of disordered materials. The technique,
based on detecting the fast growth of a fluorescence peak that is red-shifted
relative to the excitation frequency, is demonstrated explicitly by simulations
on linear Frenkel exciton chains.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
KMS states on Quantum Grammars
We consider quantum (unitary) continuous time evolution of spins on a lattice
together with quantum evolution of the lattice itself. In physics such
evolution was discussed in connection with quantum gravity. It is also related
to what is called quantum circuits, one of the incarnations of a quantum
computer. We consider simpler models for which one can obtain exact
mathematical results. We prove existence of the dynamics in both Schroedinger
and Heisenberg pictures, construct KMS states on appropriate C*-algebras. We
show (for high temperatures) that for each system where the lattice undergoes
quantum evolution, there is a natural scaling leading to a quantum spin system
on a fixed lattice, defined by a renormalized Hamiltonian.Comment: 22 page
The nesting habits of Macropis Pz. (Hym. Apoidea)
2 láminasThe solitary bees of the genus Macropis Pz. occupy a very isolated
position among other bees, and it is supposed that they represent
only remnants of a group once rich in species and at the present
time near its extinction. Besides three European species there are in
North America five other species of this genus (Friese, 1923).Peer reviewe
Editorial: Woody plants and forest ecosystems in a complex world—Ecological interactions and physiological functioning above and below ground
International audienc
- …