946 research outputs found
Anomalous low temperature state of CeOs4Sb12: Magnetic field and La-impurity study
Specific heat for single crystalline samples of Ce1-xLaxOs4Sb12 at zero-field
and magnetic fields to 14 T is reported. Our results confirm enhanced value of
the electronic specific heat coefficient in the paramagnetic state. They
provide arguments for the intrinsic origin of the 1.1 K anomaly. This
transition leads to opening of the gap at the Fermi surface. This low
temperature state of CeOs4Sb12 is extremely sensitive to chemical impurities.
2% of La substituted for Ce suppresses the transition and reduces the
electronic specific heat coefficient. The magnetic field response of the
specific heat is also anomalous.Comment: 4 pages, 3 figure
Einstein-Podolsky-Rosen-like correlation on a coherent-state basis and inseparability of two-mode Gaussian states
The strange property of the Einstein-Podolsky-Rosen (EPR) correlation between
two remote physical systems is a primitive object on the study of quantum
entanglement. In order to understand the entanglement in canonical
continuous-variable systems, a pair of the EPR-like uncertainties is an
essential tool. Here, we consider a normalized pair of the EPR-like
uncertainties and introduce a state-overlap to a classically correlated mixture
of coherent states. The separable condition associated with this state-overlap
determines the strength of the EPR-like correlation on a coherent-state basis
in order that the state is entangled. We show that the coherent-state-based
condition is capable of detecting the class of two-mode Gaussian entangled
states. We also present an experimental measurement scheme for estimation of
the state-overlap by a heterodyne measurement and a photon detection with a
feedforward operation.Comment: 9 pages, 5 figures. A part of the materials in Sec. VI B of previous
versions was moved into another paper: Journal of Atomic, Molecular, and
Optical Physics, 2012, 854693 (2012).
http://www.hindawi.com/journals/jamop/2012/854693
Exotic Kondo-hole band resistivity and magnetoresistance of CeLaOsSb alloys
Electrical resistivity measurements of non-magnetic single-crystalline
CeLaOsSb alloys, and 0.1, are reported for
temperatures down to 20 mK and magnetic fields up to 18 T. At the lowest
temperatures, the resistivity of CeLaOsSb has a
Fermi-liquid-like temperature variation , but with negative
in small fields. The resistivity has an unusually strong magnetic field
dependence for a paramagnetic metal. The 20 mK resistivity increases by 75%
between H=0 and 4 T and then decreases by 65% between 4 T and 18 T. Similarly,
the coefficient increases with the field from -77 to 29cmK between H=0 and 7 T and then decreases to 18cmK for 18 T. This nontrivial temperature and field variation
is attributed to the existence of a very narrow Kondo-hole band in the
hybridization gap, which pins the Fermi energy. Due to disorder the Kondo-hole
band has localized states close to the band edges. The resistivity for
has a qualitatively similar behavior to that of , but with a larger
Kondo-hole band
A Massive Jet Ejection Event from the Microquasar SS 433 Accompanying Rapid X-Ray Variability
Microquasars occasionally exhibit massive jet ejections which are distinct
from the continuous or quasi-continuous weak jet ejections. Because those
massive jet ejections are rare and short events, they have hardly been observed
in X-ray so far. In this paper, the first X-ray observation of a massive jet
ejection from the microquasar SS 433 with the Rossi X-ray Timing Explorer
(RXTE) is reported. SS 433 undergoing a massive ejection event shows a variety
of new phenomena including a QPO-like feature near 0.1 Hz, rapid time
variability, and shot-like activities. The shot-like activity may be caused by
the formation of a small plasma bullet. A massive jet may be consist of
thousands of those plasma bullets ejected from the binary system. The size,
mass, internal energy, and kinetic energy of the bullets and the massive jet
are estimated.Comment: 21 pages including 5 figures, submitted to Ap
Continuous Variable Quantum Cryptography using Two-Way Quantum Communication
Quantum cryptography has been recently extended to continuous variable
systems, e.g., the bosonic modes of the electromagnetic field. In particular,
several cryptographic protocols have been proposed and experimentally
implemented using bosonic modes with Gaussian statistics. Such protocols have
shown the possibility of reaching very high secret-key rates, even in the
presence of strong losses in the quantum communication channel. Despite this
robustness to loss, their security can be affected by more general attacks
where extra Gaussian noise is introduced by the eavesdropper. In this general
scenario we show a "hardware solution" for enhancing the security thresholds of
these protocols. This is possible by extending them to a two-way quantum
communication where subsequent uses of the quantum channel are suitably
combined. In the resulting two-way schemes, one of the honest parties assists
the secret encoding of the other with the chance of a non-trivial superadditive
enhancement of the security thresholds. Such results enable the extension of
quantum cryptography to more complex quantum communications.Comment: 12 pages, 7 figures, REVTe
Dynamical Semigroup Description of Coherent and Incoherent Particle-Matter Interaction
The meaning of statistical experiments with single microsystems in quantum
mechanics is discussed and a general model in the framework of non-relativistic
quantum field theory is proposed, to describe both coherent and incoherent
interaction of a single microsystem with matter. Compactly developing the
calculations with superoperators, it is shown that the introduction of a time
scale, linked to irreversibility of the reduced dynamics, directly leads to a
dynamical semigroup expressed in terms of quantities typical of scattering
theory. Its generator consists of two terms, the first linked to a coherent
wavelike behaviour, the second related to an interaction having a measuring
character, possibly connected to events the microsystem produces propagating
inside matter. In case these events breed a measurement, an explicit
realization of some concepts of modern quantum mechanics ("effects" and
"operations") arises. The relevance of this description to a recent debate
questioning the validity of ordinary quantum mechanics to account for such
experimental situations as, e.g., neutron-interferometry, is briefly discussed.Comment: 22 pages, latex, no figure
Gamma-Ray Burst and Relativistic Shells: The Surface Filling Factor
The variability observed in many complex gamma-ray bursts (GRBs) is
inconsistent with causally connected variations in a single, symmetric,
relativistic shell interacting with the ambient material ("external shocks").
Rather, the symmetry of the shell must be broken on an angular scale much
smaller than Gamma^{-1} where Gamma is the bulk Lorentz factor for the shell.
The observed variability in the external shock models arises from the number of
causally connected regions that (randomly) become active. We define the
"surface filling factor" to be the ratio of the area of causally connected
regions that become active to the observable area of the shell. From the
observed variability in 52 BATSE bursts, we estimate the surface filling factor
to be typically 0.005 although some values are near unity. We find that the
surface filling factor is about 0.1 Delta T/T in both the constant Gamma phase
(which probably produces the GRB) and the deaccelerating phase (which probably
produces the x-ray afterglows). Here, \Delta T is a typical time scale of
variability and T is the time since the initial signal. We analyze the 2 hr
flare seen by ASCA 36 hr after the GRB and conclude that the surface filling
factor must be small (0.001) in the x-ray afterglow phase as well. Explanations
for low surface filling factor can either require more or less energy (by a
factor of about 1000) compared to that expected for a symmetric shell.Comment: 26 pages, 5 embedded figures, Latex, revised version as in press,
ApJ, added figure to show the possible expanding shell geometries that can
give low filling facto
The Bose-Einstein distribution functions and the multiparticle production at high energies
The evolution properties of propagating particles produced at high energies
in a randomly distributed environment are studied. The finite size of the phase
space of the multiparticle production region as well as the chaoticity can be
derived.Comment: 18 pages, LaTeX, no figures, no table
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