9,377 research outputs found
Spectral asymptotics for large skew-symmetric perturbations of the harmonic oscillator
Originally motivated by a stability problem in Fluid Mechanics, we study the
spectral and pseudospectral properties of the differential operator on , where is a
real-valued function and a small parameter. We define
as the infimum of the real part of the spectrum of
, and as the supremum of the norm of the
resolvent of along the imaginary axis. Under appropriate
conditions on , we show that both quantities ,
go to infinity as , and we give precise
estimates of the growth rate of . We also provide an example
where is much larger than if is
small. Our main results are established using variational "hypocoercive"
methods, localization techniques and semiclassical subelliptic estimates.Comment: 38 pages, 4 figure
Creating collective many-body states with highly excited atoms
We study the collective excitation of a gas of highly excited atoms confined
to a large spacing ring lattice, where the ground and the excited states are
coupled resonantly via a laser field. Our attention is focused on the regime
where the interaction between the highly excited atoms is very weak in
comparison to the Rabi frequency of the laser. We demonstrate that in this case
the many-body excitations of the system can be expressed in terms of free
spinless fermions. The complex many-particle states arising in this regime are
characterized and their properties, e.g. their correlation functions, are
studied. In addition we investigate how one can actually experimentally access
some of these many-particle states by a temporal variation of the laser
parameters.Comment: 10 pages, 7 figure
Photoionization Rates of Cs Rydberg Atoms in a 1064 nm Far Off-Resonance Trap
Experimental measurements of photoionization rates of Rydberg
states of Cs () in a 1064 nm far off-resonance dipole trap
are presented. The photoionization rates are obtained by measuring the
lifetimes of Rydberg atoms produced inside of a 1064 nm far off-resonance trap
and comparing the lifetimes to corresponding control experiments in a
magneto-optical trap. Experimental results for the control experiments agree
with recent theoretical predictions for Rydberg state lifetimes and measured
photoionization rates are in agreement with transition rates calculated from a
model potential.Comment: 12 pages, 4 figure
Quasiclassical calculations of BBR-induced depopulation rates and effective lifetimes of Rydberg nS, nP and nD alkali-metal atoms with n < 80
Rates of depopulation by blackbody radiation (BBR) and effective lifetimes of
alkali-metal \textit{nS}, \textit{n}P and \textit{nD} Rydberg states have been
calculated in a wide range of principal quantum numbers at the
ambient temperatures of 77, 300 and 600 K. Quasiclassical formulas were used to
calculate the radial matrix elements of the dipole transitions from Rydberg
states. Good agreement of our numerical results with the available theoretical
and experimental data has been found. We have also obtained simple analytical
formulas for estimates of effective lifetimes and BBR-induced depopulation
rates, which well agree with the numerical data.Comment: 12 pages, 6 figures, 8 tables. Typo in Eq.16 corrected in V2. Typos
in Eq.5 and Eq.9 corrected in V3. Error in calculation of Rb nP_{3/2}
effective lifetimes corrected in V4: see new data in Table II and Table VII,
Erratum to be published in PR
Effect of finite detection efficiency on the observation of the dipole-dipole interaction of a few Rydberg atoms
We have developed a simple analytical model describing multi-atom signals
that are measured in experiments on dipole-dipole interaction at resonant
collisions of a few Rydberg atoms. It has been shown that finite efficiency of
the selective field-ionization detector leads to the mixing up of the spectra
of resonant collisions registered for various numbers of Rydberg atoms. The
formulas which help to estimate an appropriate mean Rydberg atom number for a
given detection efficiency are presented. We have found that a measurement of
the relation between the amplitudes of collisional resonances observed in the
one- and two-atom signals provides a straightforward determination of the
absolute detection efficiency and mean Rydberg atom number. We also performed a
testing experiment on resonant collisions in a small excitation volume of a
sodium atomic beam. The resonances observed for 1 to 4 detected Rydberg atoms
have been analyzed and compared with theory.Comment: 10 pages, 4 figures; equations 8,9,18,19,23,26-31, figures 3 and
4(d), and measurements revised in version
Ionization of Sodium and Rubidium nS, nP and nD Rydberg atoms by blackbody radiation
Results of theoretical calculations of ionization rates of Rb and Na Rydberg
atoms by blackbody radiation (BBR) are presented. Calculations have been
performed for nS, nP and nD states of Na and Rb, which are commonly used in a
variety of experiments, at principal quantum numbers n=8-65 and at three
ambient temperatures of 77, 300 and 600 K. A peculiarity of our calculations is
that we take into account the contributions of BBR-induced redistribution of
population between Rydberg states prior to photoionization and field ionization
by extraction electric field pulses. The obtained results show that these
phenomena affect both the magnitude of measured ionization rates and shapes of
their dependencies on n. The calculated ionization rates are compared with the
results of our earlier measurements of BBR-induced ionization rates of Na nS
and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states
except nS with n>15 is observed. We also present the useful analytical formulae
for quick estimation of BBR ionization rates of Rydberg atoms.Comment: 14 pages, 6 figures, 6 tables in Appendi
A comparison of star formation characteristics in different types of irregular galaxies
Two regions of recent star formation in blue irregular galaxies were observed with the IUE in the short wavelength, low dispersion mode. The spectra indicates that the massive star content is similar in these regions and is best fit by massive stars formed in a burst and now are approximately 2.5 to 3.0 million years old
Strongly correlated gases of Rydberg-dressed atoms: quantum and classical dynamics
We discuss techniques to generate long-range interactions in a gas of
groundstate alkali atoms, by weakly admixing excited Rydberg states with laser
light. This provides a tool to engineer strongly correlated phases with reduced
decoherence from inelastic collisions and spontaneous emission. As an
illustration, we discuss the quantum phases of dressed atoms with dipole-dipole
interactions confined in a harmonic potential, as relevant to experiments. We
show that residual spontaneous emission from the Rydberg state acts as a
heating mechanism, leading to a quantum-classical crossover.Comment: 4 pages, 4 figure
Spectral properties of a Rydberg atom immersed in a Bose-Einstein condensate
The electronic spectrum of a Rydberg atom immersed in a Bose-Einstein
condensate is investigated. The Heisenberg equations of motions for the
condensate and the Rydberg atom are derived. Neglecting the backaction of the
Rydberg atom onto the condensate decouples the equations describing the
condensate and Rydberg atom. In this case the spectral structure of the Rydberg
atom is completely determined by an effective potential which depends on the
density distribution of the condensate. We study the spectral properties for
the situation of an isotropic harmonic and anharmonic as well as axially
symmetric confinement. In the latter case an intriguing analogy with Rydberg
atoms in magnetic fields is encountered
Collective quantum jumps of Rydberg atoms
We study an open quantum system of atoms with long-range Rydberg interaction,
laser driving, and spontaneous emission. Over time, the system occasionally
jumps between a state of low Rydberg population and a state of high Rydberg
population. The jumps are inherently collective and in fact exist only for a
large number of atoms. We explain how entanglement and quantum measurement
enable the jumps, which are otherwise classically forbidden.Comment: 4 page
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