120 research outputs found
Self-Energy Correction to the Two-Photon Decay Width in Hydrogenlike Atoms
We investigate the gauge invariance of the leading logarithmic radiative
correction to the two-photon decay width in hydrogenlike atoms. It is shown
that an effective treatment of the correction using a Lamb-shift "potential"
leads to equivalent results in both the length as well as the velocity gauges
provided all relevant correction terms are taken into account. Specifically,
the relevant radiative corrections are related to the energies that enter into
the propagator denominators, to the Hamiltonian, to the wave functions, and to
the energy conservation condition that holds between the two photons; the form
of all of these effects is different in the two gauges, but the final result is
shown to be gauge invariant, as it should be. Although the actual calculation
only involves integrations over nonrelativistic hydrogenic Green functions, the
derivation of the leading logarithmic correction can be regarded as slightly
more complex than that of other typical logarithmic terms. The dominant
radiative correction to the 2S two-photon decay width is found to be -2.020536
(alpha/pi) (Zalpha)^2 ln[(Zalpha)^-2] in units of the leading nonrelativistic
expression. This result is in agreement with a length-gauge calculation [S. G.
Karshenboim and V. G. Ivanov, e-print physics/9702027], where the coefficient
was given as -2.025(1).Comment: 9 pages, RevTe
Two-Loop Bethe Logarithms for Higher Excited S Levels
Processes mediated by two virtual low-energy photons contribute quite
significantly to the energy of hydrogenic S states. The corresponding level
shift is of the order of (alpha/pi)^2 (Zalpha)^6 m_e c^2 and may be ascribed to
a two-loop generalization of the Bethe logarithm. For 1S and 2S states, the
correction has recently been evaluated by Pachucki and Jentschura [Phys. Rev.
Lett. vol. 91, 113005 (2003)]. Here, we generalize the approach to higher
excited S states, which in contrast to the 1S and 2S states can decay to P
states via the electric-dipole (E1) channel. The more complex structure of the
excited-state wave functions and the necessity to subtract P-state poles lead
to additional calculational problems. In addition to the calculation of the
excited-state two-loop energy shift, we investigate the ambiguity in the energy
level definition due to squared decay rates.Comment: 14 pages, RevTeX, to appear in Phys. Rev.
The Dipole Coupling of Atoms and Light in Gravitational Fields
The dipole coupling term between a system of N particles with total charge
zero and the electromagnetic field is derived in the presence of a weak
gravitational field. It is shown that the form of the coupling remains the same
as in flat space-time if it is written with respect to the proper time of the
observer and to the measurable field components. Some remarks concerning the
connection between the minimal and the dipole coupling are given.Comment: 10 pages, LaTe
Shell Structure of Exotic Nuclei
Theoretical predictions and experimental discoveries for neutron-rich,
short-lived nuclei far from stability indicate that the familiar concept of
nucleonic shell structure should be considered as less robust than previously
thought. The notion of single-particle motion in exotic nuclei is reviewed with
a particular focus on three aspects: (i) variations of nuclear mean field with
neutron excess due to tensor interactions; (ii) importance of many-body
correlations; and (iii) influence of open channels on properties of weakly
bound and unbound nuclear states.Comment: 14 pages, 7 figures, submitted to Progress in Particle and Nuclear
Physics, Proc. of the International School of Nuclear Physics 28th Course,
Radioactive Beams, Nuclear Dynamics and Astrophysics, Erice-Sicily: 16 - 24
September 200
Extension of the sum rule for the transition rates between multiplets to the multiphoton case
The sum rule for the transition rates between the components of two
multiplets, known for the one-photon transitions, is extended to the
multiphoton transitions in hydrogen and hydrogen-like ions. As an example the
transitions 3p-2p, 4p-3p and 4d-3d are considered. The numerical results are
compared with previous calculations.Comment: 10 pages, 4 table
Quantum Interferometric Optical Lithography: Exploiting Entanglement to Beat The Diffraction Limit
Classical, interferometric, optical lithography is diffraction limited to
writing features of a size lambda/2 or greater, where lambda is the optical
wavelength. Using nonclassical photon number states, entangled N at a time, we
show that it is possible to write features of minimum size lambda/(2N) in an
N-photon absorbing substrate. This result surpasses the usual classical
diffraction limit by a factor of N. Since the number of features that can be
etched on a two-dimensional surface scales inversely as the square of the
feature size, this allows one to write a factor of N^2 more elements on a
semiconductor chip. A factor of N = 2 can be achieved easily with entangled
photon pairs generated from optical parametric downconversion. It is shown how
to write arbitrary 2D patterns by using this method.Comment: 9 pages, 2 figure
Biphoton focusing for two-photon excitation
We study two-photon excitation using biphotons generated via the process of
spontaneous parametric down-conversion in a nonlinear crystal. We show that the
focusing of these biphotons yields an excitation distribution that is
essentially the same as the distribution of one-photon excitation at the pump
wavelength. We also demonstrate that biphoton excitation in the image region
yields a distribution whose axial width is approximately that of the crystal
thickness and whose transverse width is that of the pump at the input to the
crystal.Comment: Accepted for publication in Physical Review
Frequency-resolved Monte Carlo
We adapt the Quantum Monte Carlo method to the cascaded formalism of quantum optics, allowing us to simulate the emission of photons of known energy. Statistical processing of the photon clicks thus collected agrees with the theory of frequency-resolved photon correlations, extending the range of applications based on correlations of photons of prescribed energy, in particular those of a photon-counting character. We apply the technique to autocorrelations of photon streams from a two-level system under coherent and incoherent pumping, including the Mollow triplet regime where we demonstrate the direct manifestation of leapfrog processes in producing an increased rate of two-photon emission events
Polarization correlation in the two-photon decay of atomic hydrogen: nonlocality versus entanglement
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