7,973 research outputs found
Amplification of Fluctuations in a Spinor Bose Einstein Condensate
Dynamical instabilities due to spin-mixing collisions in a Rb F=1
spinor Bose-Einstein condensate are used as an amplifier of quantum spin
fluctuations. We demonstrate the spectrum of this amplifier to be tunable, in
quantitative agreement with mean-field calculations. We quantify the
microscopic spin fluctuations of the initially paramagnetic condensate by
applying this amplifier and measuring the resulting macroscopic magnetization.
The magnitude of these fluctuations is consistent with predictions of a
beyond-mean-field theory. The spinor-condensate-based spin amplifier is thus
shown to be nearly quantum-limited at a gain as high as 30 dB
Periodic spin textures in a degenerate F=1 Rb spinor Bose gas
We report on the spin textures produced by cooling unmagnetized Rb F=1
spinor gases into the regime of quantum degeneracy. At low temperatures,
magnetized textures form that break translational symmetry and display
short-range periodic magnetic order characterized by one- or two-dimensional
spatial modulations with wavelengths much smaller than the extent of the
quasi-two-dimensional degenerate gas. Spin textures produced upon cooling spin
mixtures with a non-zero initial magnetic quadrupole moment also show
ferromagnetic order that, at low temperature, coexists with the spatially
modulated structure.Comment: 6 pages, revised substantially following reviewer comments and
further analysi
Spontaneously modulated spin textures in a dipolar spinor Bose-Einstein condensate
Helical spin textures in a Rb F=1 spinor Bose-Einstein condensate are
found to decay spontaneously toward a spatially modulated structure of spin
domains. This evolution is ascribed to magnetic dipolar interactions that
energetically favor the short-wavelength domains over the long-wavelength spin
helix. This is confirmed by eliminating the dipolar interactions by a sequence
of rf pulses and observing a suppression of the formation of the short-range
domains. This study confirms the significance of magnetic dipole interactions
in degenerate Rb F=1 spinor gases
The Evolution of Luminous Compact Blue Galaxies: Disks or Spheroids?
Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies
characterized by high luminosities, blue colors, and high surface brightnesses.
Residing at the high luminosity, high mass end of the blue sequence, LCBGs sit
at the critical juncture of galaxies that are evolving from the blue to the red
sequence. Yet we do not understand what drives the evolution of LCBGs, nor how
they will evolve. Based on single-dish HI observations, we know that they have
a diverse range of properties. LCBGs are HI-rich with M(HI)=10^{9-10.5} M(sun),
have moderate M(dyn)=10^{10-12} M(sun), and 80% have gas depletion timescales
less than 3 Gyr. These properties are consistent with LCBGs evolving into
low-mass spirals or high mass dwarf ellipticals or dwarf irregulars. However,
LCBGs do not follow the Tully-Fisher relation, nor can most evolve onto it,
implying that many LCBGs are not smoothly rotating, virialized systems. GMRT
and VLA HI maps confirm this conclusion revealing signatures of recent
interactions and dynamically hot components in some local LCBGs, consistent
with the formation of a thick disk or spheroid. Such signatures and the high
incidence of close companions around LCBGs suggest that star formation in local
LCBGs is likely triggered by interactions. The dynamical masses and apparent
spheroid formation in LCBGs combined with previous results from optical
spectroscopy are consistent with virial heating being the primary mechanism for
quenching star formation in these galaxies.Comment: 4 pages, 1 figure, to appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Se
High-Resolution Magnetometry with a Spinor Bose-Einstein Condensate
We demonstrate a precision magnetic microscope based on direct imaging of the
Larmor precession of a Rb spinor Bose-Einstein condensate. This
magnetometer attains a field sensitivity of 8.3 pT/Hz over a
measurement area of 120 m, an improvement over the low-frequency field
sensitivity of modern SQUID magnetometers. The corresponding atom shot-noise
limited sensitivity is estimated to be 0.15 pT/Hz for unity duty cycle
measurement. The achieved phase sensitivity is close to the atom shot-noise
limit suggesting possibilities of spatially resolved spin-squeezed
magnetometry. This magnetometer marks a significant application of degenerate
atomic gases to metrology
Construction and testing of the optical bench for LISA pathfinder
eLISA is a space mission designed to measure gravitational radiation over a frequency range of 0.1–100 mHz (European Space Agency LISA Assessment Study Report 2011). It uses laser interferometry to measure changes of order in the separation of inertial test masses housed in spacecraft separated by 1 million km. LISA Pathfinder (LPF) is a technology demonstrator mission that will test the key eLISA technologies of inertial test masses monitored by laser interferometry in a drag-free spacecraft. The optical bench that provides the interferometry for LPF must meet a number of stringent requirements: the optical path must be stable at the few level; it must direct the optical beams onto the inertial masses with an accuracy of better than ±25 μm, and it must be robust enough not only to survive launch vibrations but to achieve full performance after launch. In this paper we describe the construction and testing of the flight optical bench for LISA Pathfinder that meets all the design requirements
The Nature of Nearby Counterparts to Intermediate Redshift Luminous Compact Blue Galaxies II. CO Observations
We present the results of a single-dish beam-matched survey of the three
lowest rotational transitions of CO in a sample of 20 local (D < 70 Mpc)
Luminous Compact Blue Galaxies (LCBGs). These ~L*, blue, high surface
brightness, starbursting galaxies were selected with the same criteria used to
define LCBGs at higher redshifts. Our detection rate was 70%, with those
galaxies having Lblue<7e9 Lsun no detected. We find the H2 masses of local
LCBGs range from 6.6e6 to 2.7e9 Msun, assuming a Galactic CO-to-H2 conversion
factor. Combining these results with our earlier HI survey of the same sample,
we find that the ratio of molecular to atomic gas mass is low, typically 5-10%.
Using a Large Velocity Gradient model, we find that the average gas conditions
of the entire ISM in local LCBGs are similar to those found in the centers of
star forming regions in our Galaxy, and nuclear regions of other galaxies. Star
formation rates, determined from IRAS fluxes, are a few solar masses per year,
much higher per unit dynamical mass than normal spirals. If this rate remains
constant, the molecular hydrogen depletion time scales are short, 10-200 Myr.Comment: accepted for publication in the ApJ (vol 625
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