779 research outputs found
Quantum simulator for the Schwinger effect with atoms in bi-chromatic optical lattices
Ultra-cold atoms in specifically designed optical lattices can be used to
mimic the many-particle Hamiltonian describing electrons and positrons in an
external electric field. This facilitates the experimental simulation of (so
far unobserved) fundamental quantum phenomena such as the Schwinger effect,
i.e., spontaneous electron-positron pair creation out of the vacuum by a strong
electric field.Comment: 4 pages, 2 figures; minor corrections and improvements in text and in
figures; references adde
Unconventional density wave in CeCoIn_5?
Very recently large Nernst effect and Seebeck effect were observed above the
superconducting transition temperature 2.3K in a heavy fermion superconductor
CeCoIn_5. We shall interpret this large Nernst effect in terms of
unconventional density wave (UDW), which appears around T=18K. Also the
temperature dependence of the Seebeck coefficient below T=18K is described in
terms of UDW. Another hallmark for UDW is the angular dependent
magnetoresistance, which should be readily accessible experimentally.Comment: 4 pages, 7 figure
QED vacuum fluctuations and induced electric dipole moment of the neutron
Quantum fluctuations in the QED vacuum generate non-linear effects, such as
peculiar induced electromagnetic fields. In particular, we show here that an
electrically neutral particle, possessing a magnetic dipole moment, develops an
induced electric dipole-type moment with unusual angular dependence, when
immersed in a quasistatic, constant external electric field. The calculation of
this effect is done in the framework of the Euler-Heisenberg effective QED
Lagrangian, corresponding to the weak field asymptotic expansion of the
effective action to one-loop order. It is argued that the neutron might be a
good candidate to probe this signal of non-linearity in QED.Comment: A misprint has been corrected, and three new references have been
adde
Observability of an induced electric dipole moment of the neutron from nonlinear QED
It has been shown recently that a neutron placed in an external quasistatic
electric field develops an induced electric dipole moment
due to quantum fluctuations in the QED vacuum. A
feasible experiment which could detect such an effect is proposed and described
here. It is shown that the peculiar angular dependence of
on the orientation of the neutron spin leads to a
characteristic asymmetry in polarized neutron scattering by heavy nuclei. This
asymmetry can be of the order of for neutrons with epithermal
energies. For thermalized neutrons from a hot moderator one still expects
experimentally accessible values of the order of . The contribution of
the induced effect to the neutron scattering length is expected to be only one
order of magnitude smaller than that due to the neutron polarizability from its
quark substructure. The experimental observation of this scattering asymmetry
would be the first ever signal of nonlinearity in electrodynamics due to
quantum fluctuations in the QED vacuum
Sauter-Schwinger like tunneling in tilted Bose-Hubbard lattices in the Mott phase
We study the Mott phase of the Bose-Hubbard model on a tilted lattice. On the
(Gutzwiller) mean-field level, the tilt has no effect -- but quantum
fluctuations entail particle-hole pair creation via tunneling. For small
potential gradients (long-wavelength limit), we derive a quantitative analogy
to the Sauter-Schwinger effect, i.e., electron-positron pair creation out of
the vacuum by an electric field. For large tilts, we obtain resonant tunneling
related to Bloch oscillations.Comment: 4 pages, 1 figur
Dynamically assisted Schwinger mechanism
We study electron-positron pair creation {from} the Dirac vacuum induced by a
strong and slowly varying electric field (Schwinger effect) which is
superimposed by a weak and rapidly changing electromagnetic field (dynamical
pair creation). In the sub-critical regime where both mechanisms separately are
strongly suppressed, their combined impact yields a pair creation rate which is
{dramatically} enhanced. Intuitively speaking, the strong electric field lowers
the threshold for dynamical particle creation -- or, alternatively, the fast
electromagnetic field generates additional seeds for the Schwinger mechanism.
These findings could be relevant for planned ultra-high intensity lasers.Comment: 4 pages, 2 figure
Birefringence and Dichroism of the QED Vacuum
We use an analytic form for the Heisenberg-Euler Lagrangian to calculate the
birefringent and dichroic properties of the vacuum for arbitrarily strong
wrenchless fields.
PACS : 12.20.Ds, 42.25.Lc 97.60.Jd, 98.70.RzComment: 8 pages, 2 figures, to appear in Journal of Physics
QED One-loop Corrections to a Macroscopic Magnetic Dipole
We consider the field equations of a static magnetic field including one-loop
QED corrections, and calculate the corrections to the field of a magnetic
dipole.
PACS: 12.20.Ds, 97.60.Jd, 97.60.GbComment: 11 pages, 4 figures, to appear in Journal of Physics
Singularity-Free Electrodynamics for Point Charges and Dipoles: Classical Model for Electron Self-Energy and Spin
It is shown how point charges and point dipoles with finite self-energies can
be accomodated into classical electrodynamics. The key idea is the introduction
of constitutive relations for the electromagnetic vacuum, which actually
mirrors the physical reality of vacuum polarization. Our results reduce to
conventional electrodynamics for scales large compared to the classical
electron radius cm. A classical simulation for a
structureless electron is proposed, with the appropriate values of mass, spin
and magnetic moment.Comment: 3 page
Thermally-induced vacuum instability in a single plane wave
Ever since Schwinger published his influential paper [J. Schwinger, Phys.
Rev. \textbf{82}, 664 (1951)], it has been unanimously accepted that the vacuum
is stable in the presence of an electromagnetic plane wave. However, we advance
an analysis that indicates this statement is not rigorously valid in a real
situation, where thermal effects are present. We show that the thermal vacuum,
in the presence of a single plane-wave field, even in the limit of zero
frequency (a constant crossed field), decays into electron-positron pairs.
Interestingly, the pair-production rate is found to depend nonperturbatively on
both the amplitude of the constant crossed field and on the temperature.Comment: 5 pages, 3 figure
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