753 research outputs found
Infra-red Divergences in Light-Front QED and Coherent State Basis
We present a next to leading order calculation of electron mass
renormalization in Light-Front Quantum Electrodynamics (LFQED) using
old-fashioned time ordered perturbation theory (TOPT). We show that the true
infrared divergences in get canceled up to if one uses
coherent state basis instead of fock basis to calculate the transition matrix
elements.Comment: 44 pages,11 figure
Phonon bottleneck in the low-excitation limit
The phonon-bottleneck problem in the relaxation of two-level systems (spins)
via direct phonon processes is considered numerically in the weak-excitation
limit where the Schroedinger equation for the spin-phonon system simplifies.
The solution for the relaxing spin excitation p(t), emitted phonons n_k(t),
etc. is obtained in terms of the exact many-body eigenstates. In the absence of
phonon damping Gamma_{ph} and inhomogeneous broadening, p(t) approaches the
bottleneck plateau p_\infty > 0 with strongly damped oscillations, the
frequency being related to the spin-phonon splitting Delta at the avoided
crossing. For any Gamma_{ph} > 0 one has p(t) -> 0 but in the case of strong
bottleneck the spin relaxation rate is much smaller than Gamma_{ph} and p(t) is
nonexponential. Inhomogeneous broadening exceeding Delta partially alleviates
the bottleneck and removes oscillations of p(t). The line width of emitted
phonons, as well as Delta, increase with the strength of the bottleneck, i.e.,
with the concentration of spins.Comment: 16 PR pages, 14 Figure captions, submitted to PRB. The whole text
does dot fit here. Please, get the correct file from
http://www.lehman.edu/faculty/dgaranin/Bottleneck2.pd
Sub-Natural Linewidth Single Photons from a Quantum Dot
The observation of quantum dot resonance fluorescence enabled a new
solid-state approach to generating single photons with a bandwidth almost as
narrow as the natural linewidth of a quantum dot transition. Here, we operate
in the Heitler regime of resonance fluorescence to generate sub-natural
linewidth and high-coherence quantum light from a single quantum dot. The
measured single-photon bandwidth exhibits a 30-fold reduction with respect to
the radiative linewidth of the QD transition and the single photons exhibit
coherence properties inherited from the excitation laser. In contrast,
intensity-correlation measurements reveal that this photon source maintains a
high degree of antibunching behaviour on the order of the transition lifetime
with vanishing two-photon scattering probability. This light source will find
immediate applications in quantum cryptography, measurement-based quantum
computing and, in particular, deterministic generation of high-fidelity
distributed entanglement among independent and even disparate quantum systems
Three and Four-Body Interactions in Spin-Based Quantum Computers
In the effort to design and to construct a quantum computer, several leading
proposals make use of spin-based qubits. These designs generally assume that
spins undergo pairwise interactions. We point out that, when several spins are
engaged mutually in pairwise interactions, the quantitative strengths of the
interactions can change and qualitatively new terms can arise in the
Hamiltonian, including four-body interactions. In parameter regimes of
experimental interest, these coherent effects are large enough to interfere
with computation, and may require new error correction or avoidance techniques.Comment: 5 pages incl. 4 figures. To appear in Phys. Rev. Lett. For an
expanded version including detailed calculations see
http://xxx.lanl.gov/abs/cond-mat/030201
Entanglement between the future and past in the quantum vacuum
We note that massless fields within the future and past light cone may be
quantized as independent systems. We show that the vacuum is an entangled state
of these systems, exactly mirroring the known entanglement between the
spacelike separated Rindler wedges. We describe a detector which exhibits a
thermal response to the vacuum when switched on at t=0. The feasibility of
experimentally detecting this effect is discussed.Comment: 4 pages, 1 figur
Quantization Of Cyclotron Motion and Quantum Hall Effect
We present a two dimensional model of IQHE in accord with the cyclotron
motion. The quantum equation of the QHE curve and a new definition of filling
factor are also given.Comment: 13 Pages, Latex, 1 figure, to appear in Europhys. Lett. September
199
New facts about muon production in Extended Air Shower simulations
Whereas air shower simulations are very valuable tools for interpreting
cosmic ray data, there is a long standing problem: is seems to be impossible to
accommodate at the same time the longitudinal development of air showers and
the number of muons measured at ground. Using a new hadronic interaction model
(EPOS) in air shower simulations produces considerably more muons, in agreement
with results from the HiRes-MIA experiment. We find that this is mainly due to
a better description of baryon-antibaryon production in hadronic interactions.
This is a new aspect of air shower physics which has never been considered so
far
Quantum derivation of the use of classical electromagnetic potentials in relativistic Coulomb excitation
We prove that a relativistic Coulomb excitation calculation in which the
classical electromagnetic field of the projectile is used to induce transitions
between target states gives the same target transition amplitudes, to all
orders of perturbation theory, as would a calculation in which the interaction
between projectile and target is mediated by a quantized electromagnetic field.Comment: 1 .zip file containing LaTex source plus three figures as .eps file
High energy cosmic-ray interactions with particles from the Sun
Cosmic-ray protons with energies above eV passing near the Sun may
interact with photons emitted by the Sun and be excited to a
resonance. When the decays, it produces pions which further decay to
muons and photons which may be detected with terrestrial detectors. A flux of
muons, photon pairs (from decay), or individual high-energy photons
coming from near the Sun would be a rather striking signature, and the flux of
these particles is a fairly direct measure of the flux of cosmic-ray nucleons,
independent of the cosmic-ray composition. In a solid angle within
around the Sun the flux of photon pairs is about \SI{1.3e-3}{}
particles/(kmyr), while the flux of muons is about \SI{0.33e-3}{}
particles/(kmyr). This is beyond the reach of current detectors like
the Telescope Array, Auger, KASCADE-Grande or IceCube. However, the muon flux
might be detectable by next-generation air shower arrays or neutrino detectors
such as ARIANNA or ARA. We discuss the experimental prospects in some detail.
Other cosmic-ray interactions occuring close to the Sun are also briefly
discussed.Comment: 8 pages, 11 figure
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