15,492 research outputs found
Effects of mixed rare earth occupancy on the low temperature properties of (R, R',R''...)Ni2Ge2 single crystals
Temperature and applied magnetic field dependent magnetization measurements
on 34 single crystalline samples of (R, R',R''...)Ni2Ge2 compounds (R, R', R'',
etc. being primarily Gd-Lu, Y), were made. These measurements reveal that,
despite extremes in local moment anisotropy, the average de Gennes parameter is
a remarkably good predictor of the paramagnetic to antiferromagnetic ordering
temperature. In addition, the pronounced metamagnetic phase transitions seen in
the low temperature phase of TbNi2Ge2 are found to be remarkably robust to high
substitution levels of Gd and 25% substitutions of other heavy rare earths
Polarization and frequency disentanglement of photons via stochastic polarization mode dispersion
We investigate the quantum decoherence of frequency and polarization
variables of photons via polarization mode dispersion in optical fibers. By
observing the analogy between the propagation equation of the field and the
Schr\"odinger equation, we develop a master equation under Markovian
approximation and analytically solve for the field density matrix. We identify
distinct decay behaviors for the polarization and frequency variables for
single-photon and two-photon states. For the single photon case, purity
functions indicate that complete decoherence for each variable is possible only
for infinite fiber length. For entangled two-photon states passing through
separate fibers, entanglement associated with each variable can be completely
destroyed after characteristic finite propagation distances. In particular, we
show that frequency disentanglement is independent of the initial polarization
status. For propagation of two photons in a common fiber, the evolution of a
polarization singlet state is addressed. We show that while complete
polarization disentanglement occurs at a finite propagation distance, frequency
entanglement could survive at any finite distance for gaussian states.Comment: 2 figure
Non-Markovian master equation for a damped oscillator with time-varying parameters
We derive an exact non-Markovian master equation that generalizes the
previous work [Hu, Paz and Zhang, Phys. Rev. D {\bf 45}, 2843 (1992)] to damped
harmonic oscillators with time-varying parameters. This is achieved by
exploiting the linearity of the system and operator solution in Heisenberg
picture. Our equation governs the non-Markovian quantum dynamics when the
system is modulated by external devices. As an application, we apply our
equation to parity kick decoupling problems. The time-dependent dissipative
coefficients in the master equation are shown to be modified drastically when
the system is driven by pulses. For coherence protection to be effective,
our numerical results indicate that kicking period should be shorter than
memory time of the bath. The effects of using soft pulses in an ohmic bath are
also discussed
The Schrodinger particle in an oscillating spherical cavity
We study a Schrodinger particle in an infinite spherical well with an
oscillating wall. Parametric resonances emerge when the oscillation frequency
is equal to the energy difference between two eigenstates of the static cavity.
Whereas an analytic calculation based on a two-level system approximation
reproduces the numerical results at low driving amplitudes, epsilon, we observe
a drastic change of behaviour when epsilon > 0.1, when new resonance states
appear bearing no apparent relation to the eigenstates of the static system.Comment: 9 pages, 6 figures, corrected typo
Quantum fluctuations in coupled dark solitons in trapped Bose-Einstein condensates
We show that the quantum fluctuations associated with the Bogoliubov
quasiparticle vacuum can be strongly concentrated inside dark solitons in a
trapped Bose Einstein condensate. We identify a finite number of anomalous
modes that are responsible for such quantum phenomena. The fluctuations in
these anomalous modes correspond to the `zero-point' oscillations in coupled
dark solitons.Comment: 4 pages, 3 figure
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