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

Anisotropic focusing characteristics of micro-domain structures within crystalline Sr_0.61Ba_0.39Nb₂O₆ : 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

Shining a Light on the Federal Reserve’s 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 Fed’s 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 Fed’s international activities should be pursued. It recommends not an overhaul of the Fed’s 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 Fed’s activities without eliminating the benefits of its institutional independence for monetary policy.https://repository.upenn.edu/pennwhartonppi/1063/thumbnail.jp

Ground‐State 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

Configuration Interaction in Two‐ and Three‐Electron 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 configuration‐interaction expansion in a complete denumerable set of single‐particle functions, with one adjustable scale parameter. The best energies for the two‐electron systems, obtained with 120‐term expansions, are E(H−) = −0.52748, E(He) = −2.90335, E(Li+) = −7.27945, and E(Be+ +) = −13.65504, in units of e2/a0. The energies for all but He are lower than any heretofore obtained with a configuration‐interaction 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 208‐term expansions, are E(22S) = −7.47369 and E(22P) = −7.40366. 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