76,848 research outputs found
De Sitter Bounces
By analytically continuing recently-found instantons, we construct
time-dependent solutions of Einstein-Maxwell de Sitter gravity which smoothly
bounce between two de Sitter phases. These deformations of de Sitter space
undergo several stages in their time evolution. Four and five-dimensional de
Sitter bounces can be lifted to non-singular time-dependent solutions of
M-theory.Comment: Latex, 18 pages, 5 figure
Mode-Locked Two-Photon States
The concept of mode locking in laser is applied to a two-photon state with
frequency entanglement. Cavity enhanced parametric down-conversion is found to
produce exactly such a state. The mode-locked two-photon state exhibits a
comb-like correlation function. An unbalanced Hong-Ou-Mandel type
interferometer is used to measure the correlation function. A revival of the
typical interference dip is observed. We will discuss schemes for engineering
of quantum states in time domain.Comment: 4 pages, 5 figure
Magneto-electric effect in NdCrTiO5
We have measured the dielectric constant and the pyroelectric current of
orthorhombic (space group ) NdCrTiO polycrystalline samples. The
dielectric constant and the pyroelectric current show features associated with
ferroelectric transitions at the antiferromagnetic transition temperature
( = 21 K). The effect of magnetic fields is to enhance the
features almost linearly up to the maximum measured field (7 T) with a
spontaneous polarization value of C/m. Two possible
scenarios, the linear magnetoelectric effect and multiferroicity
(antiferromagnetism + ferroelectricity), are discussed as possible explanations
for the observations.Comment: 7 pages, 6 figure
The Resonant Exchange Qubit
We introduce a solid-state qubit in which exchange interactions among
confined electrons provide both the static longitudinal field and the
oscillatory transverse field, allowing rapid and full qubit control via rf
gate-voltage pulses. We demonstrate two-axis control at a detuning sweet-spot,
where leakage due to hyperfine coupling is suppressed by the large exchange
gap. A {\pi}/2-gate time of 2.5 ns and a coherence time of 19 {\mu}s, using
multi-pulse echo, are also demonstrated. Model calculations that include
effects of hyperfine noise are in excellent quantitative agreement with
experiment
Unprecedented January–July Warming Recorded In A 178-year Tree-ring Width Chronology In The Dabie Mountains, Southeastern China
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Path Integral of the Two Dimensional Su-Schrieffer-Heeger Model
The equilibrium thermodynamics of the two dimensional Su-Schrieffer-Heeger
Model is derived by means of a path integral method which accounts for the
variable range of the electronic hopping processes. While the lattice degrees
of freedom are classical functions of time and are integrated out exactly, the
electron particle paths are treated quantum mechanically. The free energy of
the system and its temperature derivatives are computed by summing at any
over the ensemble of relevant particle paths which mainly contribute to the
total partition function. In the low regime, the {\it heat capacity over T}
ratio shows un upturn peculiar of a glassy like behavior. This feature is more
sizeable in the square lattice than in the linear chain as the overall hopping
potential contribution to the total action is larger in higher dimensionality.Comment: Phys.Rev.B vol.71 (2005
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