431 research outputs found
Cumulative identical spin rotation effects in collisionless trapped atomic gases
We discuss the strong spin segregation in a dilute trapped Fermi gas recently
observed by Du et al. with "anomalous" large time scale and amplitude. In a
collisionless regime, the atoms oscillate rapidly in the trap and average the
inhomogeneous external field in an energy dependent way, which controls their
transverse spin precession frequency. During interactions between atoms with
different spin directions, the identical spin rotation effect (ISRE) transfers
atoms to the up or down spin state, depending on their motional energy. Since
low energy atoms are closer to the center of the trap than high energy atoms,
the final outcome is a strong correlation between spins and positions.Comment: 4 pages, 2 figures; v2: comparison to experimental data adde
Optical excitation of nonlinear spin waves
We demonstrate a technique for exciting spin waves in an ultracold gas of
Rb-87 atoms based on tunable AC Stark potentials. This technique allows us to
excite normal modes of spin waves with arbitrary amplitudes in the trapped gas,
including dipole, quadrupole, octupole, and hexadecapole modes. These modes
exhibit strong nonlinearities, which manifest as amplitude dependence of the
excitation frequencies and departure from sinusoidal behavior. Our results are
in good agreement with a full treatment of a quantum Boltzmann transport
equation.Comment: 11 pages, 5 figure
Charge identification for spectral lines in nitrogen
Ion charge identification for spectral lines in nitrogen by beam foil light source techniqu
The mean lives of some excited levels in nitrogen 1
Beam foil measurements of multiplet mean lives in nitrogen deca
The existence of a 2Po excited state for the e+Ca system
The Configuration Interaction method is used to demonstrate that there is an
electronically stable state of positronic calcium with an orbital angular
momentum of L=1. This prediction relies on the use of an asymptotic series to
estimate the variational limit of the energy. The best estimate of the binding
energy is 37 meV. A discussion of the structure of the system is also
presented.Comment: 4 pages, 2 figures, in press PR
Internal state conversion in ultracold gases
We consider an ultracold gas of (non-condensed) bosons or fermions with two
internal states, and study the effect of a gradient of the transition frequency
between these states. When a RF pulse is applied to the sample,
exchange effects during collisions transfer the atoms into internal states
which depend on the direction of their velocity. This results, after a short
time, in a spatial separation between the two states. A kinetic equation is
solved analytically and numerically; the results agree well with the recent
observations of Lewandowski et al.Comment: Accepted version, to appear in PR
Beam-foil spectrum of nitrogen at ultraviolet wavelengths
Spectrum analysis on foil excited nitrogen beam during acceleration at ultraviolet wavelength
Femtosecond transparency in the extreme ultraviolet
Electromagnetically induced transparency-like behavior in the extreme
ultraviolet (XUV) is studied theoretically, including the effect of intense 800
nm laser dressing of He 2s2p (1Po) and 2p^2 (1Se) autoionizing states. We
present an ab initio solution of the time-dependent Schrodinger equation (TDSE)
in an LS-coupling configuration interaction basis set. The method enables a
rigorous treatment of optical field ionization of these coupled autoionizing
states into the N = 2 continuum in addition to N = 1. Our calculated transient
absorption spectra show encouraging agreement with experiment.Comment: 25 pages, 7 figures, 1 tabl
Resource-efficient technology to produce 4-aminodiphenylamine
A critical analysis of the existing and emerging methods for preparation of 4-aminodiphenylamine has been conducted. It is noted that, in economic and environmental terms, the promising methods are based on condensation of aniline with nitrobenzene in an alkaline medium, followed by hydrogenation of the resulting intermediates. Using the above method for industrial production of 4-ADPA will help eliminate principal shortcomings inherent in the existing industrial methods: reduce unit operations of the process, use more accessible, inexpensive raw materials, increase product yield, eliminate formation of carcinogenic substances, significantly decrease the formation of waste products and, most importantly, decrease the volume of waste water. The most promising methods for industrial production are recent discoveries that use heterogeneous catalysts during condensation of aniline with nitrobenzene, e.g., zeolite ZSM-5 treated with tetramethylammonium hydroxide or highly basic anions which considerably simplify production technology and process control, lower costs and comply with strict environmental requirements
Spin self-rephasing and very long coherence times in a trapped atomic ensemble
We perform Ramsey spectroscopy on the ground state of ultra-cold 87Rb atoms
magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities
over the sample should limit the 1/e contrast decay time to about 3 s, while
decay times of 58 s are actually observed. We explain this surprising result by
a spin self-rephasing mechanism induced by the identical spin rotation effect
originating from particle indistinguishability. We propose a theory of this
synchronization mechanism and obtain good agreement with the experimental
observations. The effect is general and susceptible to appear in other physical
systems.Comment: Revised version; improved description of the theoretical treatmen
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