7,576 research outputs found
Decoherence properties of arbitrarily long histories
Within the decoherent histories formulation of quantum mechanics, we consider
arbitrarily long histories constructed from a fixed projective partition of a
finite-dimensional Hilbert space. We review some of the decoherence properties
of such histories including simple necessary decoherence conditions and the
dependence of decoherence on the initial state. Here we make a first step
towards generalization of our earlier results [Scherer and Soklakov, e-print:
quant-ph/0405080, (2004) and Scherer et al., Phys. Lett. A, vol. 326, 307,
(2004)] to the case of approximate decoherence.Comment: 8 pages, no figure
Picosecond pumpâprobe and polarization techniques in supersonic molecular beams: Measurement of ultrafast vibrational-rotational dephasing and coherence
In the last few years, the time-resolved dynamics of collisionless intramolecular vibrational-energy redistribution (IVR) [1] has been probed [2] using picosecond excitation and fluorescence detection. By this method new information on IVR, coherence and photochemical changes (e.g., trans-cis isomerization) has been obtained. [2,3] However, in a number of cases the (early time) primary step following picosecond excitation could not be resolved simply because the time resolution was limited to ~50ps
Initial states and decoherence of histories
We study decoherence properties of arbitrarily long histories constructed
from a fixed projective partition of a finite dimensional Hilbert space. We
show that decoherence of such histories for all initial states that are
naturally induced by the projective partition implies decoherence for arbitrary
initial states. In addition we generalize the simple necessary decoherence
condition [Scherer et al., Phys. Lett. A (2004)] for such histories to the case
of arbitrary coarse-graining.Comment: 10 page
Direct picosecond time resolution of unimolecular reactions initiated by local mode excitation
The concept of local mode (LM) states [1] in large molecules raises the possibilty of inducing chemical reactions from a well-defined initial state (bond-selective chemistry). The results of linewidth and energy measurements in gases, [2(a)] and low temperature solids, [2(b)] however, indicate that the relaxation times for such high energy (> 15000 cm^-1) states can be extremely short, < 1ps. Because of the lack of direct time-resolved measurements, the following fundamental questions have not been unequivocally answered: What are the homogeneous linewidths of LM states and what are the rates of energy relaxation or reaction out of these states? Over the past five years we have made several attempts to observe the picosecond dynamics of LM states. Due to the inherent difficulties associated with making these measurements, such as the very small oscillator strength (Ï < 10^-23 cm^2), an extremely sensitive probing technique becomes imperative
Diffractive lens fabricated with binary features less than 60 nm
We designed, fabricated, and characterized a binary diffractive lens with features less than 60nm. The lens was designed for operation in the red portion of the spectrum. Experimental measurements of lens performance agree with predictions generated by rigorous models of diffraction
Elemental surface analysis at ambient pressure by electron-induced x-ray fluorescence
The development of a portable surface elemental analysis tool, based on the excitation of characteristic x rays from samples at ambient pressure with a focused electron beam is described. This instrument relies on the use of a thin electron transmissive membrane to isolate the vacuum of the electron source from the ambient atmosphere. The major attributes of this instrument include rapid (several minutes) spectrum acquisition, nondestructive evaluation of elemental composition, no sample preparation, and high-to-medium (several hundreds ”m) spatial resolution. The instrument proof-of-principle has been demonstrated in a laboratory setup by obtaining energy dispersive x-ray spectra from metal and mineral samples
Electromagnetic Corrections in Partially Quenched Chiral Perturbation Theory
We introduce photons in Partially Quenched Chiral Perturbation Theory and
calculate the resulting electromagnetic loop-corrections at NLO for the charged
meson masses and decay constants. We also present a numerical analysis to
indicate the size of the different corrections. We show that several
phenomenologically relevant quantities can be calculated consistently with
photons which couple only to the valence quarks, allowing the use of gluon
configurations produced without dynamical photons.Comment: 11 page
Classical predictability and coarse-grained evolution of the quantum baker's map
We investigate how classical predictability of the coarse-grained evolution
of the quantum baker's map depends on the character of the coarse-graining. Our
analysis extends earlier work by Brun and Hartle [Phys. Rev. D 60, 123503
(1999)] to the case of a chaotic map. To quantify predictability, we compare
the rate of entropy increase for a family of coarse-grainings in the decoherent
histories formalism. We find that the rate of entropy increase is dominated by
the number of scales characterising the coarse-graining.Comment: 28 pages, 1 figur
Noise in Al single electron transistors of stacked design
We have fabricated and examined several Al single electron transistors whose
small islands were positioned on top of a counter electrode and hence did not
come into contact with a dielectric substrate. The equivalent charge noise
figure of all transistors turned out to be surprisingly low, (2.5 - 7)*10E-5
e/sqrt(Hz) at f = 10 Hz. Although the lowest detected noise originates mostly
from fluctuations of background charge, the noise contribution of the tunnel
junction conductances was, on occasion, found to be dominant.Comment: 4 pages of text with 1 table and 5 figure
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