Efficient Two-dimensional Subrecoil Raman Cooling of Atoms in a Tripod Configuration

We present an efficient method for subrecoil cooling of neutral atoms by applying Raman cooling in 2D to a four-level tripod-system. The atoms can be cooled simultaneously in two directions using only three laser beams. We describe the cooling process with a simple model showing that the momentum distribution can be rapidly narrowed to velocity spread down to $0.1v_\text{rec}$, corresponding to effective temperature equal to $0.01T_\text{rec}$. This method opens new possibilities for cooling of neutral atoms.Comment: 6 pages, 3 figure

Robust two-dimensional subrecoil Raman cooling by adiabatic transfer in a tripod atomic system

We demonstrate two-dimensional robust Raman cooling in a four-level tripod system, in which velocity-selective population transfer is achieved by a STIRAP pulse. In contrast to basic 2D Raman cooling with square envelope pulses [Phys. Rev. A 83, 023407 (2011)], the technique presented here allows for a wide variation in the pulse duration and amplitude once the adiabaticity criterion is satisfied. An efficient population transfer together with attaining of a narrow spread of the resonant-velocity group leads to the narrowing of the velocity-distribution spread down to $0.1v_\mathrm{rec}$, corresponding to an effective temperature equal to $0.01 T_\mathrm{rec}$. This robust method opens new possibilities for cooling of neutral atoms.Comment: 8 pages, 3 figure

Oral Interviews for Testing in the High-School Spanish Classroom

Our project offers strategies and materials for the beginning Spanish classroom to increase oral proficiency of students through an emphasis on individual and small-group interviews with the teacher, which will be an integral part to every classroom test. These interviews will be referred to also as “One-On-One orals,” “OOOs,” or simply “encounters,” inspired by the oral proficiency interviews (OPIs) first developed in the 1980s to measure speaker competence in a second language--as per the proficiency guidelines of the American Council for the Teaching of Foreign Languages (ACTFL). (Our project’s classroom materials begin on page 5.) As we know today, the speaking competencies that the OPIs strive for and measure have shaped much of the evolution of our classroom teaching. Now, with this project, the goal is to use test-day interviews that parallel the OPI as a way to further develop speaking abilities and consolidate grammatical concepts and vocabulary. The interviews can be as simple as having students communicate prepared/practiced material in Spanish to the instructor face to face--while the rest of the class is completing written portions of the exam. Our project will details sample interviews to help teachers imagine what they themselves might try (see page 5). We also provide some suggestions for technology use and share an activity that is outside the scope of the testing interview but can be a fun way to encourage classroom speaking (pages 12-15)

Dimensions of infinitely generated self-affine sets and restricted digit sets for signed Lüroth expansions

For countably infinite IFSs on ℝ2 consisting of affine contractions with diagonal linear parts, we give conditions under which the affinity dimension is an upper bound for the Hausdorff dimension and a lower bound for the lower box-counting dimension. Moreover, we identify a family of countably infinite IFSs for which the Hausdorff and affinity dimension are equal, and which have full dimension spectrum. The corresponding self-affine sets are related to restricted digit sets for signed L\"uroth expansions

Collective molecule formation in a degenerate Fermi gas via a Feshbach resonance

We model collisionless collective conversion of a degenerate Fermi gas into bosonic molecules via a Feshbach resonance, treating the bosonic molecules as a classical field and seeding the pairing amplitudes with random phases. A dynamical instability of the Fermi sea against association into molecules initiates the conversion. The model qualitatively reproduces several experimental observations {[Regal et al., Nature {\bf 424}, 47 (2003)]}. We predict that the initial temperature of the Fermi gas sets the limit for the efficiency of atom-molecule conversion.Comment: 4 pages, 3 figures, 10+ references, accepted to PR

Tailoring of motional states in double-well potentials by time-dependent processes

We show that the vibrational state tailoring method developed for molecular systems can be applied for cold atoms in optical lattices. The original method is based on a three-level model interacting with two strong laser pulses in a counterintuitive sequence [M. Rodriguez et al., Phys. Rev. A 62, 053413 (2000)]. Here we outline the conditions for achieving similar dynamics with single time-dependent potential surfaces. It is shown that guided switching between diabatic and adiabatic evolution has an essential role in this system. We also show that efficient and precise tailoring of motional states in optical lattices can be achieved, for instance, simply by superimposing two lattices and moving them with respect to each other.Comment: 9 pages, 11 figures, 25 references; accepted to PRA; v2: minor explanatory remarks added & typos correcte