42,619 research outputs found
Ambipolar Electric Field, Photoelectrons, and their Role in Atmospheric Escape From Hot-jupiters
Atmospheric mass-loss from Hot-jupiters can be large due to the close
proximity of these planets to their host star and the strong radiation the
planetary atmosphere receives. On Earth, a major contribution to the
acceleration of atmospheric ions comes from the vertical separation of ions and
electrons, and the generation of the ambipolar electric field. This process,
known as the "polar wind", is responsible for the transport of ionospheric
constituents to the Earth's magnetosphere, where they are well observed. The
polar wind can also be enhanced by a relatively small fraction of super-thermal
electrons (photoelectrons) generated by photoionization. We formulate a
simplified calculation of the effect of the ambipolar electric field and the
photoelectrons on the ion scale-height in a generalized manner. We find that
the ion scale-height can be increased by a factor of 2-15 due to the polar wind
effects. We also estimate a lower limit of an order of magnitude increase of
the ion density and the atmospheric mass-loss rate when polar wind effects are
included.Comment: 7 pages, 3 figures, accepted to ApJ Letter
Narrow band microwave radiation from a biased single-Cooper-pair transistor
We show that a single-Cooper-pair transistor (SCPT) electrometer emits
narrow-band microwave radiation when biased in its sub-gap region. Photo
activation of quasiparticle tunneling in a nearby SCPT is used to
spectroscopically detect this radiation, in a configuration that closely mimics
a qubit-electrometer integrated circuit. We identify emission lines due to
Josephson radiation and radiative transport processes in the electrometer, and
argue that a dissipative superconducting electrometer can severely disrupt the
system it attempts to measure.Comment: 4 pages, 3 figure
Thermal effects on lattice strain in hcp Fe under pressure
We compute the c/a lattice strain versus temperature for nonmagnetic hcp iron
at high pressures using both first-principles linear response quasiharmonic
calculations based on the full potential linear-muffin-tin-orbital (LMTO)
method and the particle-in-cell (PIC) model for the vibrational partition
function using a tight-binding total-energy method. The tight-binding model
shows excellent agreement with the all-electron LMTO method. When hcp structure
is stable, the calculated geometric mean frequency and Helmholtz free energy of
hcp Fe from PIC and linear response lattice dynamics agree very well, as does
the axial ratio as a function of temperature and pressure. On-site
anharmonicity proves to be small up to the melting temperature, and PIC gives a
good estimate of its sign and magnitude. At low pressures, hcp Fe becomes
dynamically unstable at large c/a ratios, and the PIC model might fail where
the structure approaches lattice instability. The PIC approximation describes
well the vibrational behavior away from the instability, and thus is a
reasonable approach to compute high temperature properties of materials. Our
results show significant differences from earlier PIC studies, which gave much
larger axial ratio increases with increasing temperature, or reported large
differences between PIC and lattice dynamics results.Comment: 9 figure
First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures
We investigate the equation of state and elastic properties of hcp iron at
high pressures and high temperatures using first principles linear response
linear-muffin-tin-orbital method in the generalized-gradient approximation. We
calculate the Helmholtz free energy as a function of volume, temperature, and
volume-conserving strains, including the electronic excitation contributions
from band structures and lattice vibrational contributions from quasi-harmonic
lattice dynamics. We perform detailed investigations on the behavior of elastic
moduli and equation of state properties as functions of temperature and
pressure, including the pressure-volume equation of state, bulk modulus, the
thermal expansion coefficient, the Gruneisen ratio, and the shock Hugoniot.
Detailed comparison has been made with available experimental measurements and
theoretical predictions.Comment: 33 pages, 12 figure
First-principles thermoelasticity of bcc iron under pressure
We investigate the elastic and isotropic aggregate properties of
ferromagnetic bcc iron as a function of temperature and pressure by computing
the Helmholtz free energies for the volume-conserving strained structures using
the first-principles linear response linear-muffin-tin-orbital method and the
generalized-gradient approximation. We include the electronic excitation
contributions to the free energy from the band structures, and phonon
contributions from quasi-harmonic lattice dynamics. We make detailed
comparisons between our calculated elastic moduli and their temperature and
pressure dependences with available experimental and theoretical data.Comment: 5 figures, 2 table
Balanced homodyne detectors in QFT
Within the dipole approximation we describe the interaction of a photodiode
with the quantum electric field. The diode is modelled by an electron in a
bound state which upon interaction, treated perturbatively in the paper, can
get excited to one of the scattering states. We furthermore analyze a balanced
homodyne detector (BHD) with a local oscillator (LO) consisting of two
photodiodes illuminated by a monochromatic coherent state. We show, that to the
leading order the BHD's output measures the expectation value of the quantum
electric field, in the state without the LO, restricted to the frequency of the
LO. The square of the output measures the two-point function of the quantum
field. This shows that the BHDs provide tools for measurements of sub-vacuum
(negative) expectation values of the squares quantum fields and thus for test
of Quantum Energy Inequality - like bounds, or other QFT effects under the
influence of external conditions.Comment: Revised version with minor mistakes remove
Distillation of GHZ states by selective information manipulation
Methods for distilling maximally entangled tripartite (GHZ) states from
arbitrary entangled tripartite pure states are described. These techniques work
for virtually any input state. Each technique has two stages which we call
primary and secondary distillation. Primary distillation produces a GHZ state
with some probability, so that when applied to an ensemble of systems, a
certain percentage is discarded. Secondary distillation produces further GHZs
from the discarded systems. These protocols are developed with the help of an
approach to quantum information theory based on absolutely selective
information, which has other potential applications.Comment: minor corrections, especially of some numerical values; conclusions
unaffecte
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