1,535 research outputs found
Neutrino induced coherent pion production
Neutrino-induced coherent pion production is an important channel for the
study of neutrino-nucleus interactions. It is both a dangerous background
for Îœe oscillation experiments, and a critical component required for precise
understanding of neutrino-nucleus pion production in general.
The body of experimental evidence for coherent pion production at high
neutrino energies is reviewed. This data is described well by the Rein-Sehgal
model, which is described and studied. In light of recent low energy limits
set below the Rein-Sehgal model cross-section an alternative low energy
model, the Alvarez-Ruso model, was implemented in the neutrino interaction
simulation GENIE. The results of this simulation are compared with those
from the Rein-Sehgal model, and briefly with those from other models.
Finally, a search for ΜΌ-induced charged-current (CC) coherent pion production
on 12C was conducted at a mean neutrino energy of 0.86 GeV, using data
from the T2K experiment's off-axis near detector. A 3.0 Ï excess of events
was found above the background prediction, constituting the first experimental
evidence of CC coherent pion production below 7 GeV. Preliminary attempts
to interpret this excess in the context of the Rein-Sehgal and Alvarez-Ruso
models found cross-sections consistent with the limits set by SciBooNE
Raman Adiabatic Transfer of Optical States
We analyze electromagnetically induced transparency and light storage in an
ensemble of atoms with multiple excited levels (multi-Lambda configuration)
which are coupled to one of the ground states by quantized signal fields and to
the other one via classical control fields. We present a basis transformation
of atomic and optical states which reduces the analysis of the system to that
of EIT in a regular 3-level configuration. We demonstrate the existence of dark
state polaritons and propose a protocol to transfer quantum information from
one optical mode to another by an adiabatic control of the control fields
Dynamics of a two-level system coupled with a quantum oscillator in the very strong coupling limit
The time-dependent behavior of a two-level system interacting with a quantum
oscillator system is analyzed in the case of a coupling larger than both the
energy separation between the two levels and the energy of quantum oscillator
(, where is the frequency of the
transition between the two levels, is the frequency of the
oscillator, and is the coupling between the two-level system and the
oscillator). Our calculations show that the amplitude of the expectation value
of the oscillator coordinate decreases as the two-level system undergoes the
transition from one level to the other, while the transfer probability between
the levels is staircase-like. This behavior is explained by the interplay
between the adiabatic and the non-adiabatic regimes encountered during the
dynamics with the system acting as a quantum counterpart of the Landau-Zener
model. The transition between the two levels occurs as long as the expectation
value of the oscillator coordinate is driven close to zero. On the contrary, if
the initial conditions are set such that the expectation values of the
oscillator coordinate are far from zero, the system will remain locked on one
level.Comment: 4 pages, 4 figures, to be published in Physical Review
Using a qubit to measure photon number statistics of a driven, thermal oscillator
We demonstrate theoretically how photon number statistics of a driven, damped
oscillator at finite temperature can be extracted by measuring the dephasing
spectrum of a two-level system dispersively coupled to the oscillator; we thus
extend the work of Dykman (1987) and Gambetta et al. (2006). We carefully
consider the fidelity of this scheme-- to what extent does the measurement
reflect the initial number statistics of the mode? We also derive analytic
results for the dephasing of a qubit by a driven, thermal mode, and compare
results obtained at different levels of approximation. Our results have
relevance both to experiments in circuit cavity QED, as well as to
nano-electromechanical systems.Comment: 11 pages; 2 figures adde
Cold Collision Frequency Shift in Two-Dimensional Atomic Hydrogen
We report a measurement of the cold collision frequency shift in atomic
hydrogen gas adsorbed on the surface of superfluid 4He at T<=90 mK. Using
two-photon electron and nuclear magnetic resonance in 4.6 T field we separate
the resonance line shifts due to the dipolar and exchange interactions, both
proportional to surface density sigma. We find the clock shift Delta v_c =
-1.0(1)x10^-7 Hz cm^-2 x sigma, which is about 100 times smaller than the value
predicted by the mean field theory and known scattering lengths in the 3D case.Comment: 4 pages, 3 figure
Polarization entanglement visibility of photon pairs emitted by a quantum dot embedded in a microcavity
We study the photon emission from a quantum dot embedded in a microcavity.
Incoherent pumping of its excitons and biexciton provokes the emission of leaky
and cavity modes. By solving a master equation we obtain the correlation
functions required to compute the spectrum and the relative efficiency among
the emission of pairs and single photons. A quantum regime appears for low
pumping and large rate of emission. By means of a post-selection process, a two
beams experiment with different linear polarizations could be performed
producing a large polarization entanglement visibility precisely in the quantum
regime.Comment: 13 pages and 6 figure
Slow light in paraffin-coated Rb vapor cells
We present preliminary results from an experimental study of slow light in
anti-relaxation-coated Rb vapor cells, and describe the construction and
testing of such cells. The slow ground state decoherence rate allowed by coated
cell walls leads to a dual-structured electromagnetically induced transparency
(EIT) spectrum with a very narrow (<100 Hz) transparency peak on top of a broad
pedestal. Such dual-structure EIT permits optical probe pulses to propagate
with greatly reduced group velocity on two time scales. We discuss ongoing
efforts to optimize the pulse delay in such coated cell systems.Comment: 6 pages, 6 figures, submitted to Journal of Modern Optic
Dynamics of the excitations of a quantum dot in a microcavity
We study the dynamics of a quantum dot embedded in a three-dimensional
microcavity in the strong coupling regime in which the quantum dot exciton has
an energy close to the frequency of a confined cavity mode. Under the
continuous pumping of the system, confined electron and hole can recombine
either by spontaneous emission through a leaky mode or by stimulated emission
of a cavity mode that can escape from the cavity. The numerical integration of
a master equation including all these effects gives the dynamics of the density
matrix. By using the quantum regression theorem, we compute the first and
second order coherence functions required to calculate the photon statistics
and the spectrum of the emitted light. Our main result is the determination of
a range of parameters in which a state of cavity modes with poissonian or
sub-poissonian (non-classical) statistics can be built up within the
microcavity. Depending on the relative values of pumping and rate of stimulated
emission, either one or two peaks close to the excitation energy of the dot
and/or to the natural frequency of the cavity are observed in the emission
spectrum. The physics behind these results is discussed
Synchronization and bistability of qubit coupled to a driven dissipative oscillator
We study numerically the behavior of qubit coupled to a quantum dissipative
driven oscillator (resonator). Above a critical coupling strength the qubit
rotations become synchronized with the oscillator phase. In the synchronized
regime, at certain parameters, the qubit exhibits tunneling between two
orientations with a macroscopic change of number of photons in the resonator.
The life times in these metastable states can be enormously large. The
synchronization leads to a drastic change of qubit radiation spectrum with
appearance of narrow lines corresponding to recently observed single
artificial-atom lasing [O. Astafiev {\it et al.} Nature {\bf 449}, 588 (2007)].Comment: revtex 4 pages, 6 figs, research at http://www.quantware.ups-tlse.fr
Collapse-and-revival dynamics of strongly laser-driven electrons
The relativistic quantum dynamics of an electron in an intense single-mode
quantized electromagnetic field is investigated with special emphasis on the
spin degree of freedom. In addition to fast spin oscillations at the laser
frequency, a second time scale is identified due to the intensity dependent
emissions and absorptions of field quanta. In analogy to the well-known
phenomenon in atoms at moderate laser intensity, we put forward the conditions
of collapses and revivals for the spin evolution in laser-driven electrons
starting at feasible W/cm.Comment: 18 pages, 4 figure
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