3,115 research outputs found
Low-energy scattering of electrons and positrons in liquids
The scattering of low energy electrons and positrons is described for the liquid phase and compared and contrasted with that for the gas phase. Similarities as well as differences are noted. The loci of scattering sites, called spurs in the liquid phase, are considered in detail. In particular, their temporal and spatial evolution is considered from the point of view of scattering. Two emphases are made: one upon the stochastic calculation of the distribution of distances required for slowing down to thermal velocities, and the other upon the calculation of cross sections for energy loss by means of quantum mechanics
Patient's breath controls comfort devices
Patient assist system for totally disabled persons was developed which permits a person, so paralyzed as to be unable to move, to activate by breathing, a call system to summon assistance, turn the page of a book, ajust his bed, or do any one of a number of other things. System consists of patient assist control and breath actuated switch
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Analytical treatment of stabilization
We present a summarizing account of a series of investigations whose central topic is to address the question whether atomic stabilization exists in an analytical way. We provide new aspects on several issues of the matter in the theoretical context when the dynamics is described by the Stark Hamiltonian. The main outcome of these studies is that the governing parameters for this phenomenon are the total classical momentum transfer and the total classical displacement. Whenever these two quantities vanish, asymptotically weak stabilization does exist. For all other situations we did not find any evidence for stabilization. We found no evidence that strong stabilization might occur. Our results agree qualitatively with the existing experimental findings
A neutral atom quantum register
We demonstrate the realization of a quantum register using a string of single
neutral atoms which are trapped in an optical dipole trap. The atoms are
selectively and coherently manipulated in a magnetic field gradient using
microwave radiation. Our addressing scheme operates with a high spatial
resolution and qubit rotations on individual atoms are performed with 99%
contrast. In a final read-out operation we analyze each individual atomic
state. Finally, we have measured the coherence time and identified the
predominant dephasing mechanism for our register.Comment: 4 pages, 4 figure
Adiabatic Quantum State Manipulation of Single Trapped Atoms
We use microwave induced adiabatic passages for selective spin flips within a
string of optically trapped individual neutral Cs atoms. We
position-dependently shift the atomic transition frequency with a magnetic
field gradient. To flip the spin of a selected atom, we optically measure its
position and sweep the microwave frequency across its respective resonance
frequency. We analyze the addressing resolution and the experimental robustness
of this scheme. Furthermore, we show that adiabatic spin flips can also be
induced with a fixed microwave frequency by deterministically transporting the
atoms across the position of resonance.Comment: 4 pages, 4 figure
Coherence properties and quantum state transportation in an optical conveyor belt
We have prepared and detected quantum coherences with long dephasing times at
the level of single trapped cesium atoms. Controlled transport by an "optical
conveyor belt" over macroscopic distances preserves the atomic coherence with
slight reduction of coherence time. The limiting dephasing effects are
experimentally identified and are of technical rather than fundamental nature.
We present an analytical model of the reversible and irreversible dephasing
mechanisms. Coherent quantum bit operations along with quantum state transport
open the route towards a "quantum shift register" of individual neutral atoms.Comment: 4 pages, 3 figure
A quantum group version of quantum gauge theories in two dimensions
For the special case of the quantum group we present an alternative approach to quantum gauge theories in
two dimensions. We exhibit the similarities to Witten's combinatorial approach
which is based on ideas of Migdal. The main ingredient is the Turaev-Viro
combinatorial construction of topological invariants of closed, compact
3-manifolds and its extension to arbitrary compact 3-manifolds as given by the
authors in collaboration with W. Mueller.Comment: 6 pages (plain TeX
Positronic lithium, an electronically stable Li-e ground state
Calculations of the positron-Li system were performed using the Stochastic
Variational Method and yielded a minimum energy of -7.53208 Hartree for the L=0
ground state. Unlike previous calculations of this system, the system was found
to be stable against dissociation into the Ps + Li channel with a binding
energy of 0.00217 Hartree and is therefore electronically stable. This is the
first instance of a rigorous calculation predicting that it is possible to
combine a positron with a neutral atom and form an electronically stable bound
state.Comment: 11 pages, 2 tables. To be published in Phys.Rev.Let
Relativistic coupled-cluster single-double calculations of positron-atom bound states
Relativistic coupled-cluster single-double approximation is used to calculate
positron-atom bound states. The method is tested on closed-shell atoms such as
Be, Mg, Ca, Zn, Cd, and Hg where a number of accurate calculations is
available. It is then used to calculate positron binding energies for a range
of open-shell transition metal atoms from Sc to Cu, from Y to Pd, and from Lu
to Pt. These systems possess Feshbach resonances, which can be used to search
for positron-atom binding experimentally through resonant annihilation or
scattering.Comment: submitted to Phys. Rev.
Scattering Theory Approach to Random Schroedinger Operators in One Dimension
Methods from scattering theory are introduced to analyze random Schroedinger
operators in one dimension by applying a volume cutoff to the potential. The
key ingredient is the Lifshitz-Krein spectral shift function, which is related
to the scattering phase by the theorem of Birman and Krein. The spectral shift
density is defined as the "thermodynamic limit" of the spectral shift function
per unit length of the interaction region. This density is shown to be equal to
the difference of the densities of states for the free and the interacting
Hamiltonians. Based on this construction, we give a new proof of the Thouless
formula. We provide a prescription how to obtain the Lyapunov exponent from the
scattering matrix, which suggest a way how to extend this notion to the higher
dimensional case. This prescription also allows a characterization of those
energies which have vanishing Lyapunov exponent.Comment: 1 figur
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