5,927 research outputs found
Stabilization of collapse and revival dynamics by a non-Markovian phonon bath
Semiconductor quantum dots (QDs) have been demonstrated to be versatile
candidates to study the fundamentals of light-matter interaction [1-3]. In
contrast with atom optics, dissipative processes are induced by the inherent
coupling to the environment and are typically perceived as a major obstacle
towards stable performances in experiments and applications [4].
In this paper we show that this is not necessarily the case. In fact, the
memory of the environment can enhance coherent quantum optical effects. In
particular, we demonstrate that the non-Markovian coupling to an incoherent
phonon bath has a stabilizing effect on the coherent QD cavity-quantum
electrodynamics (cQED) by inhibiting irregular oscillations and boosting
regular collapse and revival patterns. For low photon numbers we predict QD
dynamics that deviate dramatically from the well-known atomic Jaynes-Cummings
model. Our proposal opens the way to a systematic and deliberate design of
photon quantum effects via specifically engineered solid-state environments.Comment: 5 pages, 4 figure
Covariant transverse-traceless projection for secondary gravitational waves
Second-order tensor modes induced by nonlinear gravity are a key component of
the cosmological background of gravitational waves. A detection of this
background would allow us to probe the primordial power spectrum at otherwise
inaccessible scales. Usually, the energy density of these gravitational waves
is studied within perturbation theory in a particular gauge -- a connection
between our physical spacetime and a fictitious background. It is a widely
recognized issue that the second-order, scalar-induced gravitational waves are
gauge dependent. This issue arises because they are not well-defined as tensors
in the physical spacetime at second-order and are thus unphysical. In this
paper, we propose the covariant transverse-traceless projection of the
extrinsic curvature to study cosmological gravitational waves on a spatial
hypersurface. We define a new energy density which is based purely on spacetime
tensors, independent of perturbation theory, and thus is gauge invariant by
definition. We show that, in the context of second-order perturbation theory,
this new energy density contains only propagating modes in the constant-time
hypersurface in the Newtonian gauge. We further show that we can recover the
same gravitational waves after a transformation to the synchronous gauge, so
long as we correctly identify the Newtonian hypersurface.Comment: 14 pages, 2 figure, major revisio
Comparative study of macroscopic quantum tunneling in Bi_2Sr_2CaCu_2O_y intrinsic Josephson junctions with different device structures
We investigated macroscopic quantum tunneling (MQT) of
BiSrCaCuO intrinsic Josephson junctions (IJJs) with two device
structures. One is a nanometer-thick small mesa structure with only two or
three IJJs and the other is a stack of a few hundreds of IJJs on a narrow
bridge structure. Experimental results of switching current distribution for
the first switching events from zero-voltage state showed a good agreement with
the conventional theory for a single Josephson junction, indicating that a
crossover temperature from thermal activation to MQT regime for the former
device structure was as high as that for the latter device structure. Together
with the observation of multiphoton transitions between quantized energy levels
in MQT regime, these results strongly suggest that the observed MQT behavior is
intrinsic to a single IJJ in high- cuprates, independent of device
structures. The switching current distribution for the second switching events
from the first resistive state, which were carefully distinguished from the
first switchings, was also compared between two device structures. In spite of
the difference in the heat transfer environment, the second switching events
for both devices were found to show a similar temperature-independent behavior
up to a much higher temperature than the crossover temperature for the first
switching. We argue that it cannot be explained in terms of the self-heating
owing to dissipative currents after the first switching. As possible
candidates, the MQT process for the second switching and the effective increase
of electronic temperature due to quasiparticle injection are discussed.Comment: 10pages, 7figures, submitted to Phys. Rev.
Determination of signal molecules that contribute to the antimesothelioma effect of a vitamin E analogue
Strong lensing in the Einstein-Straus solution
We analyse strong lensing in the Einstein-Straus solution with positive
cosmological constant. For concreteness we compare the theory to the light
deflection of the lensed quasar SDSS J1004+4112.Comment: 14 pages, 3 figures, 5 tables. To the memory of J\"urgen Ehlers v2
contains a note added during publication in GRG and less typo
Possibility of valence-fluctuation mediated superconductivity in Cd-doped CeIrIn probed by In-NQR
We report on a pressure-induced evolution of exotic superconductivity and
spin correlations in CeIr(InCd) by means of
In-Nuclear-Quadrupole-Resonance (NQR) studies. Measurements of an NQR spectrum
and nuclear-spin-lattice-relaxation rate have revealed that
antiferromagnetism induced by the Cd-doping emerges locally around Cd dopants,
but superconductivity is suddenly induced at = 0.7 and 0.9 K at 2.34 and
2.75 GPa, respectively. The unique superconducting characteristics with a large
fraction of the residual density of state at the Fermi level that increases
with differ from those for anisotropic superconductivity mediated by
antiferromagnetic correlations. By incorporating the pressure dependence of the
NQR frequency pointing to the valence change of Ce, we suggest that
unconventional superconductivity in the CeIr(InCd) system may
be mediated by valence fluctuations.Comment: Accepted for publication in Physical Review Letter
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