76 research outputs found
Superconductivity at 11.3 K induced by cobalt doping in CeOFeAs
Pure phases of a new oxyarsenide superconductor of the nominal composition
CeOFe0.9Co0.1As was successfully synthesized by solid state reaction in sealed
silica ampoules at 1180 C. It crystallizes in the layered tetragonal ZrCuSiAs
type structure (sp gp P4/nmm) with lattice parameter of a = 3.9918(5) angstrom
and c = 8.603(1) angstrom. A sharp superconducting transition is observed at
11.31 K with an upper critical field of 45.22 T at ambient pressure. The
superconducting transition temperature is drastically lowered (~ 4.5, 4.9 K) on
increasing the concentration (x = 0.15, 0.2) of cobalt
Laser induced breakdown of the magnetic field reversal symmetry in the propagation of unpolarized light
We show how a medium, under the influece of a coherent control field which is
resonant or close to resonance to an appropriate atomic transition, can lead to
very strong asymmetries in the propagation of unpolarized light when the
direction of the magnetic field is reversed. We show how EIT can be used to
mimic effects occuring in natural systems and that EIT can produce very large
asymmetries as we use electric dipole allowed transitions. Using density matrix
calculations we present results for the breakdown of the magnetic field
reversal symmetry for two different atomic configurations.Comment: RevTex, 6 pages, 10 figures, Two Column format, submitted to Phys.
Rev.
Superconductivity in CeO_{1-x}F_xFeAs with upper critical field of 94 T
We have successfully synthesized Ce based oxypnictide with fluorine doping
(CeO_{1-x}F_xFeAs) by a two step solid state reaction method. Detailed XRD and
EDX confirm the crystal structure and chemical compositions. We observe that an
extremely high Hc2(0) of 94 T can be achieved in the x = 0.1 composition. This
increase in Hc2(0) is accompanied by a decrease in transition temperature (38.4
K in x = 0.1 composition) from 42.5 K for the x = 0.2 phase. The in-plane
Ginzburg-Landau coherence length is estimated to be ~ 27 A at x = 0.2
suggesting a moderate anisotropy in this class of superconductors. The Seebeck
coefficient confirms the majority carrier to be electrons and strong dominance
of electron-electron correlations in this multiband superconductor
Quantum interference in the fluorescence of a molecular system
It has been observed experimentally [H.R. Xia, C.Y. Ye, and S.Y. Zhu, Phys.
Rev. Lett. {\bf 77}, 1032 (1996)] that quantum interference between two
molecular transitions can lead to a suppression or enhancement of spontaneous
emission. This is manifested in the fluorescent intensity as a function of the
detuning of the driving field from the two-photon resonance condition. Here we
present a theory which explains the observed variation of the number of peaks
with the mutual polarization of the molecular transition dipole moments. Using
master equation techniques we calculate analytically as well as numerically the
steady-state fluorescence, and find that the number of peaks depends on the
excitation process. If the molecule is driven to the upper levels by a
two-photon process, the fluorescent intensity consists of two peaks regardless
of the mutual polarization of the transition dipole moments. If the excitation
process is composed of both a two-step one-photon process and a one-step,
two-photon process, then there are two peaks on transitions with parallel
dipole moments and three peaks on transitions with antiparallel dipole moments.
This latter case is in excellent agreement with the experiment.Comment: 11 pages, including 8 figure
Interference-induced gain in Autler-Townes doublet of a V-type atom in a cavity
We study the Autler-Townes spectrum of a V-type atom coupled to a
single-mode, frequency-tunable cavity field at finite termperature, with a
pre-selected polarization in the bad cavity limit, and show that, when the mean
number of thermal photons and the excited sublevel splitting is very
large (the same order as the cavity linewidth), the probe gain may occur at
either sideband of the doublet, depending on the cavity frequency, due to the
cavity-induced interference.Comment: Minor changes are mad
Cavity implementation of quantum interference in a -type atom
A scheme for engineering quantum interference in a -type atom
coupled to a frequency-tunable, single-mode cavity field with a pre-selected
polarization at finite temperature is proposed. Interference-assisted
population trapping, population inversions and probe gain at one sideband of
the Autler-Townes spectrum are predicted for certain cavity resonant
frequencies.Comment: 2 postscript figures are adde
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
Quantum interference in a driven two-level atom
We show that a dynamical suppression of spontaneous emission, predicted for a three-level atom [S.-Y. Zhu and M. O. Scully, Phys. Rev. Lett. 76, 388 (1996)] can occur in a two-level atom driven by st polychromatic field. We find that the quantum interference, responsible for the cancellation of spontaneous emission, appears between different channels of transitions among the dressed states of the driven atom. We discuss the effect for bichromatic and trichromatic (amplitude-modulated) fields and fmd that these two cases lead to the cancellation of spontaneous emission in different parts of the fluorescence spectrum. Our system has the advantage of being easily accessible by current experiments. [S1050-2947(99)50712-9]
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