1,537 research outputs found
Photon tunneling through absorbing dielectric barriers
Using a recently developed formalism of quantization of radiation in the
presence of absorbing dielectric bodies, the problem of photon tunneling
through absorbing barriers is studied. The multilayer barriers are described in
terms of multistep complex permittivities in the frequency domain which satisfy
the Kramers--Kronig relations. From the resulting input--output relations it is
shown that losses in the layers may considerably change the photon tunneling
times observed in two-photon interference experiments. It is further shown that
for sufficiently large numbers of layers interference fringes are observed that
cannot be related to a single traversal time.Comment: 17 pages LaTeX, 9 figures (PS) include
Charge Transfer and Charge Transport on the Double Helix
We present a short review of various experiments that measure charge transfer
and charge transport in DNA. Some general comments are made on the possible
connection between 'chemistry-style' charge transfer experiments that probe
fluorescence quenching and remote oxidative damage and 'physics-style'
measurements that measure transport properties as defined typically in the
solid-state. We then describe measurements performed by our group on the
millimeter wave response of DNA. By measuring over a wide range of humidity
conditions and comparing the response of single strand DNA and double strand
DNA, we show that the appreciable AC conductivity of DNA is not due to photon
assisted hopping between localized states, but instead due to dissipation from
dipole motion in the surrounding water helix.Comment: 7 pages, 3 figure
Recommended from our members
The relative effectiveness of the lecture-demonstration method and an experimental method in the teaching of general science.
STM Studies of TbTe3: Evidence for a fully Incommensurate Charge Density Wave
We observe unidirectional charge density wave ordering on the cleaved surface
of TbTe3 with a Scanning Tunneling Microscope at ~6 K. The modulation
wave-vector q_{CDW} as determined by Fourier analysis is 0.71 +/- 0.02 * 2
pi/c. (Where c is one edge of the in-plane 3D unit cell.) Images at different
tip-sample voltages show the unit cell doubling effects of dimerization and the
layer below. Our results agree with bulk X-ray measurements, with the addition
of ~(1/3) * 2 pi/a ordering perpendicular to the CDW. Our analysis indicates
that the CDW is incommensurate.Comment: 4 pages, 4 figure
Competition between Superconductivity and Charge Density Wave Ordering in the LuIr(SiGe) Alloy System
We have performed bulk measurements such as dc magnetic susceptibility,
electrical resistivity and heat capacity on the pseudo-ternary alloys
LuIr(SiGe) to study the interplay and competition
between superconductivity and the charge density wave (CDW) ordering
transition. We track the evolution of the superconducting transition
temperature T and the CDW ordering temperature T as a function
of x (concentration of Ge) (). We find that increasing x
(increasing disorder) suppresses the T rapidly with the concomitant
increase in T. We present a temperature-concentration (or volume) phase
diagram for this system and compare our results with earlier work on
substitution at the Lu or Ir site to show how dilution at the Si site presents
a different situation from these other works. The heat capacity data in the
vicinity of the CDW transition has been analyzed using a model of critical
fluctuations in addition to a mean-field contribution and a smooth lattice
background. We find that the critical exponents change appreciably with
increasing disorder. This analysis suggests that the strong-coupling and non
mean-field like CDW transition in the parent compound LuIrSi
changes to a mean-field like transition with increasing Ge concentration.Comment: 14 pages and 8 figures. Accepted for publication in Phys. Rev.
Entanglement degradation of a two-mode squeezed vacuum in absorbing and amplifying optical fibers
Applying the recently developed formalism of quantum-state transformation at
absorbing dielectric four-port devices [L.~Kn\"oll, S.~Scheel, E.~Schmidt,
D.-G.~Welsch, and A.V.~Chizhov, Phys. Rev. A {\bf 59}, 4716 (1999)], we
calculate the quantum state of the outgoing modes of a two-mode squeezed vacuum
transmitted through optical fibers of given extinction coefficients. Using the
Peres--Horodecki separability criterion for continuous variable systems
[R.~Simon, Phys. Rev. Lett. {\bf 84}, 2726 (2000)], we compute the maximal
length of transmission of a two-mode squeezed vacuum through an absorbing
system for which the transmitted state is still inseparable. Further, we
calculate the maximal gain for which inseparability can be observed in an
amplifying setup. Finally, we estimate an upper bound of the entanglement
preserved after transmission through an absorbing system. The results show that
the characteristic length of entanglement degradation drastically decreases
with increasing strength of squeezing.Comment: Paper presented at the International Conference on Quantum Optics and
VIII Seminar on Quantum Optics, Raubichi, Belarus, May 28-31, 2000, 11 pages,
LaTeX2e, 4 eps figure
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