13,531 research outputs found
Coupling between internal spin dynamics and external degrees of freedom in the presence of colored noise
We observe asymmetric transition rates between Zeeman levels (spin-flips) of
magnetically trapped atoms. The asymmetry strongly depends on the spectral
shape of an applied noise. This effect follows from the interplay between the
internal states of the atoms and their external degrees of freedom, where
different trapped levels experience different potentials. Such insight may
prove useful for controlling atomic states by the introduction of noise, as
well as provide a better understanding of the effect of noise on the coherent
operation of quantum systems.Comment: 5 pages, 4 figures; accepted to PR
High-Resolution Spectroscopy of FUors
High-resolution spectroscopy was obtained of the FUors FU Ori and V1057 Cyg
between 1995 and 2002 with SOFIN at NOT and with HIRES at Keck I. During those
years FU Ori remained about 1 mag. (in B) below its 1938-39 maximum brightness,
but V1057 Cyg (B ~ 10.5 at peak in 1970-71) faded from about 13.5 to 14.9 and
then recovered slightly. Their photospheric spectra resemble a rotating G0 Ib
supergiant, with v_eq sin i = 70 km/s for FU Ori and 55 km/s for V1057 Cyg. As
V1057 Cyg faded, P Cyg structure in Halpha and the IR CaII lines strengthened
and a complex shortward-displaced shell spectrum increased in strength,
disappeared in 1999, and reappeared in 2001. Night-to-night changes in the wind
structure of FU Ori show evidence of sporadic infall. The strength of P Cyg
absorption varied cyclically with a period of 14.8 days, with phase stability
maintained over 3 seasons, and is believed to be the rotation period. The
structure of the photospheric lines also varies cyclically, but with a period
of 3.54 days. A similar variation may be present in V1057 Cyg. As V1057 Cyg has
faded, the emission lines of a pre-existing low-excitation chromosphere have
emerged, so we believe the `line doubling' in V1057 Cyg is produced by these
central emission cores in the absorption lines, not by orbital motion in an
inclined Keplerian disk. No dependence of v_eq sin i on wavelength or
excitation potential was detected in either star, again contrary to expectation
for a self-luminous accretion disk. Nor are critical lines in the near infrared
accounted for by synthetic disk spectra. A rapidly rotating star near the edge
of stability (Larson 1980), can better explain these observations. FUor
eruptions may not be a property of ordinary TTS, but may be confined to a
special subspecies of rapid rotators having powerful quasi-permanent winds.Comment: 41 pages (including 32 figures and 9 tables); ApJ, in press; author
affiliation, figs. 3 and 9 correcte
The Schwarzschild black hole as a point particle
The description of a point mass in general relativity (GR) is given in the
framework of the field formulation of GR where all the dynamical fields,
including the gravitational field, are considered in a fixed background
spacetime. With the use of stationary (not static) coordinates non-singular at
the horizon, the Schwarzschild solution is presented as a point-like field
configuration in a whole background Minkowski space. The requirement of a
stable -causality stated recently in [J.B.Pitts and W.C.Schieve, Found.
Phys., v. 34, 211 (2004)] is used essentially as a criterion for testing
configurations.Comment: LATEX, 8 pages, no figure
Production of a Fermi gas of atoms in an optical lattice
We prepare a degenerate Fermi gas of potassium atoms by sympathetic cooling
with rubidium atoms in a one-dimensional optical lattice. In a tight lattice we
observe a change of the density of states of the system, which is a signature
of quasi two dimensional confinement. We also find that the dipolar
oscillations of the Fermi gas along the tight lattice are almost completely
suppressed.Comment: 4 pages, 4 figures, revised versio
Realization of an Excited, Strongly-Correlated Quantum Gas Phase
Ultracold atomic physics offers myriad possibilities to study strongly
correlated many-body systems in lower dimensions. Typically, only ground state
phases are accessible. Using a tunable quantum gas of bosonic cesium atoms, we
realize and control in one dimensional geometry a highly excited quantum phase
that is stabilized in the presence of attractive interactions by maintaining
and strengthening quantum correlations across a confinement-induced resonance.
We diagnose the crossover from repulsive to attractive interactions in terms of
the stiffness and the energy of the system. Our results open up the
experimental study of metastable excited many-body phases with strong
correlations and their dynamical properties
Generation of higher derivatives operators and electromagnetic wave propagation in a Lorentz-violation scenario
We study the perturbative generation of higher-derivative operators as
corrections to the photon effective action, which are originated from a Lorentz
violation background. Such corrections are obtained, at one-loop order, through
the proper-time method, using the zeta function regularization. We focus over
the lowest order corrections and investigate their influence in the propagation
of electromagnetic waves through the vacuum, in the presence of a strong,
constant magnetic field. This is a setting of experimental relevance, since it
bases active efforts to measure non linear electromagnetic effects. After
surprising cancellations of Lorentz violating corrections to the Maxwell's
equation, we show that no effects of the kind of Lorentz violation we consider
can be detected in such a context.Comment: v2: 13 pages, no figures, section IV considerably rewritten, main
results unchanged and are now obtained in a simpler way. To appear in PL
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