25,273 research outputs found
Dephasing in Quantum Dots: Quadratic Coupling to Acoustic Phonons
A microscopic theory of optical transitions in quantum dots with
carrier-phonon interaction is developed. Virtual transitions into higher
confined states with acoustic phonon assistance add a quadratic phonon coupling
to the standard linear one, thus extending the independent Boson model. Summing
infinitely many diagrams in the cumulant, a numerically exact solution for the
interband polarization is found. Its full time dependence and the absorption
lineshape of the quantum dot are calculated. It is the quadratic interaction
which gives rise to a temperature-dependent broadening of the zero-phonon line,
being here calculated for the first time in a consistent scheme.Comment: 4 pages, 2 figure
Evaluation of the importance of spin-orbit couplings in the nonadiabatic quantum dynamics with quantum fidelity and with its efficient "on-the-fly" ab initio semiclassical approximation
We propose to measure the importance of spin-orbit couplings (SOCs) in the
nonadiabatic molecular quantum dynamics rigorously with quantum fidelity. To
make the criterion practical, quantum fidelity is estimated efficiently with
the multiple-surface dephasing representation (MSDR). The MSDR is a
semiclassical method that includes nuclear quantum effects through interference
of mixed quantum-classical trajectories without the need for the Hessian of
potential energy surfaces. Two variants of the MSDR are studied, in which the
nuclei are propagated either with the fewest-switches surface hopping or with
the locally mean field dynamics. The fidelity criterion and MSDR are first
tested on one-dimensional model systems amenable to numerically exact quantum
dynamics. Then, the MSDR is combined with "on-the-fly" computed electronic
structure to measure the importance of SOCs and nonadiabatic couplings (NACs)
in the photoisomerization dynamics of CH2NH2+ considering 20 electronic states
and in the collision of F + H2 considering six electronic states.Comment: 9 pages, 3 figures, submitted to J. Chem. Phy
Spatially resolved photo ionization of ultracold atoms on an atom chip
We report on photo ionization of ultracold magnetically trapped Rb atoms on
an atom chip. The atoms are trapped at 5 K in a strongly anisotropic
trap. Through a hole in the chip with a diameter of 150 m two laser beams
are focussed onto a fraction of the atomic cloud. A first laser beam with a
wavelength of 778 nm excites the atoms via a two photon transition to the 5D
level. With a fiber laser at 1080 nm the excited atoms are photo ionized.
Ionization leads to depletion of the atomic density distribution observed by
absorption imaging. The resonant ionization spectrum is reported. The setup
used in this experiment is not only suitable to investigate BEC ion mixtures
but also single atom detection on an atom chip
High-temperature ferroelectric order and magnetic field-cooled effect driven magnetoelectric coupling in R2BaCuO5 (R= Er, Dy, Sm)
The high-temperature ferroelectric order and a remarkable magnetoelectric
effect driven by the magnetic field cooling are reported in R2BaCuO5 (R = Er,
Dy, Sm) series. The ferroelectric (FE) orders are observed at much higher
temperatures than their magnetic orders for all three members. The value of FE
Curie temperature (TFE) is considerably high as ~ 235 K with the polarization
value (P) of ~ 1410 {\mu}C/m2 for a 4 kV/cm poling field in case of Er2BaCuO5,
whereas the values of TFE and P are also promising as ~ 232 K and ~ 992
{\mu}C/m2 for Dy2BaCuO5, and ~ 184 K and ~ 980 {\mu}C/m2 for Sm2BaCuO5. The
synchrotron diffraction studies of Dy2BaCuO5 confirm a structural transition at
TFE to a polar Pna21 structure, which correlates the FE order. An unusual
magnetoelectric coupling is observed below the R order for Er and Dy compounds
and below the Cu order for Sm compound, when the pyroelectric current is
recorded only with the magnetic field both in heating and cooling cycles i.e.
typical magnetic field cooled effect. The magnetic field cooled effect driven
emergence of polarization is ferroelectric in nature, as it reverses due to the
opposite poling field. The unexplored R2BaCuO5 series attracts the community
for large TFE, high P value, and strange magnetoelectric consequences.Comment: 9 figures and 2 supporting figure
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