8,667 research outputs found
Phase separation and pair condensation in a spin-imbalanced 2D Fermi gas
We study a two-component quasi-two-dimensional Fermi gas with imbalanced spin
populations. We probe the gas at different interaction strengths and
polarizations by measuring the density of each spin component in the trap and
the pair momentum distribution after time of flight. For a wide range of
experimental parameters, we observe in-trap phase separation characterized by
the appearance of a spin-balanced condensate surrounded by a polarized gas. Our
momentum space measurements indicate pair condensation in the imbalanced gas
even for large polarizations where phase separation vanishes, pointing to the
presence of a polarized pair condensate. Our observation of zero momentum pair
condensates in 2D spin-imbalanced gases opens the way to explorations of more
exotic superfluid phases that occupy a large part of the phase diagram in lower
dimensions
Probing quench dynamics across a quantum phase transition into a 2D Ising antiferromagnet
Simulating the real-time evolution of quantum spin systems far out of
equilibrium poses a major theoretical challenge, especially in more than one
dimension. We experimentally explore the dynamics of a two-dimensional Ising
spin system with transverse and longitudinal fields as we quench it across a
quantum phase transition from a paramagnet to an antiferromagnet. We realize
the system with a near unit-occupancy atomic array of over 200 atoms obtained
by loading a spin-polarized band insulator of fermionic lithium into an optical
lattice and induce short-range interactions by direct excitation to a low-lying
Rydberg state. Using site-resolved microscopy, we probe the correlations in the
system after a sudden quench from the paramagnetic state and compare our
measurements to exact calculations in the regime where it is possible. We
achieve many-body states with longer-range antiferromagnetic correlations by
implementing a near-adiabatic quench and study the buildup of correlations as
we cross the quantum phase transition at different rates
Swift UVOT Observations of Core-Collapse SNe
We review recent UV observations of core-collapse supernovae (SNe) with the
Swift Ultra-violet/Optical Telescope (UVOT) during its first two years.
Rest-frame UV photometry is useful for differentiating SN types by exploiting
the UV-optical spectral shape and more subtle UV features. This is useful for
the real-time classification of local and high-redshift SNe using only
photometry. Two remarkable SNe Ib/c were observed with UVOT -- SN2006jc was a
UV bright SN Ib. Swift observations of GRB060218/SN2006aj began shortly after
the explosion and show a UV-bright peak followed by a UV-faint SN bump. UV
observations are also useful for constraining the temperature and ionization
structure of SNe IIP. Rest-frame UV observations of all types are important for
understanding the extinction, temperature, and bolometric luminosity of SNe and
to interpret the observations of high redshift SNe observed at optical
wavelengths.Comment: Figures are enlarged and colorized from print versio
Shining a Light on the Federal Reserveâs Foreign Affairs
Throughout its history, the U.S. Federal Reserve has engaged in international diplomacy, outside the bounds of (and sometimes in conflict with) the priorities of the White House and U.S. State Department. In directing monetary policy, the Fedâs primary concern is to benefit the U.S. economy. In the process, the Fed at times acts in concert with foreign central banks, as was the case in setting new bank regulations after the 2008 financial crisis. At other times, the Fed acts in ways that other countries view as detrimental to their economic interests. Either way, the Fed operates with little public accountability and can wind up complicating the work of U.S. diplomats. This issue brief focuses on the questions of whether and how greater oversight of the Fedâs international activities should be pursued. It recommends not an overhaul of the Fedâs structure or the elimination of its role in international affairs but instead calls for greater disclosure of its international activities. The Fed should provide testimony to Congress twice per year on its foreign policies, just as it does for monetary and regulatory policy. This kind of disclosure permits broader discussion of the Fedâs activities without eliminating the benefits of its institutional independence for monetary policy.https://repository.upenn.edu/pennwhartonppi/1063/thumbnail.jp
GroundâState Wavefunctions and Energies for the Helium Isoelectronic Series through Z = 10
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69577/2/JCPSA6-47-8-3077-1.pd
Anisotropic focusing characteristics of micro-domain structures within crystalline Sr<sub>0.61</sub>Ba<sub>0.39</sub>Nb<sub>2</sub>O<sub>6</sub> : the crystal ball
We report the anisotropic focusing characteristics of a spherically configured region of micro-domains that have been induced within a cubic shaped crystal of Ce:doped Sr0.61Ba0.39Nb2O6. The internal spherical structure focuses extraordinary polarised light, but not ordinary polarised. The spherical region, which is easily observed via scattering, is formed as the crystal cools down, after a repoling cycle through the Curie temperature, with an applied field. Analytic modelling of the thermal gradients that exist within the crystal during cooling reveals a small (< 1°) temperature difference between the central and outside regions. The similarity in shape between these temperature profiles and the observed scattering region suggests a possible mechanism for the growth of this spherical micro-domained structure
Configuration Interaction in Twoâ and ThreeâElectron Atoms
The ground states of the first four members of the helium isoelectronic series and the 22S and 22P states of lithium are calculated using a configurationâinteraction expansion in a complete denumerable set of singleâparticle functions, with one adjustable scale parameter. The best energies for the twoâelectron systems, obtained with 120âterm expansions, are E(Hâ) = â0.52748, E(He) = â2.90335, E(Li+) = â7.27945, and E(Be+ +) = â13.65504, in units of e2/a0. The energies for all but He are lower than any heretofore obtained with a configurationâinteraction approach. The dependence of energy on scale factor is found to be very pronounced, in contrast to the corresponding behavior for wavefunctions which contain the interparticle coordinates explicitly. The best energies for the lithium states, obtained with 208âterm expansions, are E(22S) = â7.47369 and E(22P) = â7.40366. The 22S energy is not as good as has been obtained with either expansions in terms of interparticle coordinates or configuration interaction with many nonlinear parameters. The 22P energy is of approximately the same accuracy but is lower than any previously published.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70610/2/JCPSA6-45-11-4248-1.pd
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