97 research outputs found
All They Want Is to Gain Attention : Press Coverage and the Selma-to-Montgomery March
March in Alabama can be a beautiful month with warm days, cool nights, flowers bursting from the ground with vibrant yellows, reds, and violets, and greens everywhere. Jonquils push through the ground like horns resounding with the song of spring and forsythia adorns itself ingold.1 March can also fulfill the proverb “comes in like a lion, goes out like a lamb.” Alabama’s March of 1965 offered cold, wet, windy weather up until the end. But a different wind blew through Selma that month—the wind of discontent and change.
For the first three months of 1965, Dr. Martin Luther King, Jr.’s Southern Christian Leadership Conference (SCLC), had conducted a voter registration drive in central Alabama’s Black Belt counties. King sought to expose voting barriers in this part of the South as a means of eliminating them nation-wide through federal legislation.2 Press coverage would be vital, focusing attention on the problem he sought to correct.
Settlers originally called the counties bordering the Alabama River the Black Belt because the rich limestone soil had become dark loam through the centuries. But the name also assumed an ethnological meaning; a majority of inhabitants descended from slaves who once worked its antebellum plantations. In 1965, those land-holdings still dotted the countryside, and many features of the old order still flourished. Contrasts also marked the region: majestic homes and ramshackle shanties, opulence and poverty, white and black, played against the endless sweep of cotton fields. In the midst of this Black Belt, athwart the Alabama River, sat Dallas County. Selma, on the river’s north bank almost in the center of both county and state, served as the county seat.
Measurement of the Zero Crossing in a Feshbach Resonance of Fermionic 6-Li
We measure a zero crossing in the scattering length of a mixture of the two
lowest hyperfine states of 6-Li. To locate the zero crossing, we monitor the
decrease in temperature and atom number arising from evaporation in a CO2 laser
trap as a function of magnetic field B. The temperature decrease and atom loss
are minimized for B=528(4) G, consistent with no evaporation. We also present
preliminary calculations using potentials that have been constrained by the
measured zero crossing and locate a broad Feshbach resonance at approximately
860 G, in agreement with previous theoretical predictions. In addition, our
theoretical model predicts a second and much narrower Feshbach resonance near
550 G.Comment: Five pages, four figure
Robust Online Hamiltonian Learning
In this work we combine two distinct machine learning methodologies,
sequential Monte Carlo and Bayesian experimental design, and apply them to the
problem of inferring the dynamical parameters of a quantum system. We design
the algorithm with practicality in mind by including parameters that control
trade-offs between the requirements on computational and experimental
resources. The algorithm can be implemented online (during experimental data
collection), avoiding the need for storage and post-processing. Most
importantly, our algorithm is capable of learning Hamiltonian parameters even
when the parameters change from experiment-to-experiment, and also when
additional noise processes are present and unknown. The algorithm also
numerically estimates the Cramer-Rao lower bound, certifying its own
performance.Comment: 24 pages, 12 figures; to appear in New Journal of Physic
On the Fulde-Ferrell State in Spatially Isotropic Superconductors
Effects of superconducting fluctuations on the Fulde-Ferrell (FF) state are
discussed in a spatially isotropic three-dimensional superconductor under a
magnetic field. For this system, Shimahara recently showed that within the
phenomenological Ginzburg-Landau theory, the long-range order of the FF state
is suppressed by the phase fluctuation of the superconducting order parameter.
[H. Shimahara: J. Phys. Soc. Jpn. {\bf 67} (1998) 1872, Physica B {\bf 259-261}
(1999) 492] In this letter, we investigate this instability of the FF state
against superconducting fluctuations from the microscopic viewpoint, employing
the theory developed by Nozi\'eres and Schmitt-Rink in the BCS-BEC crossover
field. Besides the absence of the second-order phase transition associated with
the FF state, we show that even if the pairing interaction is weak, the shift
of the chemical potential from the Fermi energy due to the fluctuations is
crucial near the critical magnetic field of the FF state obtained within the
mean-field theory.Comment: 11 pages, 1 figur
Microscopic Structure of a Vortex Line in a Superfluid Fermi Gas
The microscopic properties of a single vortex in a dilute superfluid Fermi
gas at zero temperature are examined within the framework of self-consistent
Bogoliubov-de Gennes theory. Using only physical parameters as input, we study
the pair potential, the density, the energy, and the current distribution.
Comparison of the numerical results with analytical expressions clearly
indicates that the energy of the vortex is governed by the zero-temperature BCS
coherence length.Comment: 4 pages, 4 embedded figures. Added references. To be published in
Physical Review Letter
All-Optical Production of a Degenerate Fermi Gas
We achieve degeneracy in a mixture of the two lowest hyperfine states of
Li by direct evaporation in a CO laser trap, yielding the first
all-optically produced degenerate Fermi gas. More than atoms are
confined at temperatures below K at full trap depth, where the Fermi
temperature for each state is K. This degenerate two-component mixture
is ideal for exploring mechanisms of superconductivity ranging from Cooper
pairing to Bose condensation of strongly bound pairs.Comment: 4 pgs RevTeX with 2 eps figs, to be published in Phys. Rev. Let
Two-species mixture of quantum degenerate Bose and Fermi gases
We have produced a macroscopic quantum system in which a Li-6 Fermi sea
coexists with a large and stable Na-23 Bose-Einstein condensate. This was
accomplished using inter-species sympathetic cooling of fermionic Li-6 in a
thermal bath of bosonic Na-23
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