Collisional shifts in optical-lattice atom clocks

We theoretically study the effects of elastic collisions on the determination of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom clocks. Interparticle interactions of bosonic atoms in multiply-occupied lattice sites can cause a linear frequency shift, as well as generate asymmetric Ramsey fringe patterns and reduce fringe visibility due to interparticle entanglement. We propose a method of reducing these collisional effects in an optical lattice by introducing a phase difference of $\pi$ between the Ramsey driving fields in adjacent sites. This configuration suppresses site to site hopping due to interference of two tunneling pathways, without degrading fringe visibility. Consequently, the probability of double occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure

Late Pleistocene-Holocene productivity record of benthic foraminifera from the Iceland Plateau (Core PS1246-2)

Benthic foraminiferal assemblage patterns in Core PS 1246-2 from the Iceland Plateau are examined as they relate to annual productivity and seasonal productivity changes during the Late Pleistocene glacial (23,000-11,000 yrs B.P.), Younger Dryas cool period (11,000-10,000 yrs B.P.) and Holocene (10,000-2,900 yrs B.P.). Abundance fluctuations of Cibicidoides wuellerstorji, a suspension-feeder, are used as the proxy for annual productivity, while fluctuations of the phytodetritus-exploiting species Epistoininclln r ~ i p r a E, ponides tlinzid~illisa nd GloDocossidlrliiia strbglobosa are used as the indicators of seasonal productivity. These records show seasonal productivity began to increase around 22,500 yrs B.P. and experienced three subsequent peaks in the glacial, while annual productivity increased around 16,000 yrs B.P. and shows only one peak in the glacial. The Younger Dryas shows a decrease in both seasonal and annual productivity records. Seasonal productivity in the early Holocene is much higher than during the glacial, yet appears more extreme. The Holocene record of annualproductivity continues to show a strong general increase in intensity

Last interglacial ocean changes in the Bahamas: climate teleconnections between low and high latitudes

Paleorecords and modeling studies suggest that instabilities in the Atlantic Meridional Overturning Circulation (AMOC) strongly affect the low-latitude climate, namely via feedbacks on the Atlantic Intertropical Convergence Zone (ITCZ). Despite the pronounced millennial-scale overturning and climatic variability documented in the subpolar North Atlantic during the last interglacial period (MIS 5e), studies on cross-latitudinal teleconnections remain very limited. This precludes a full understanding of the mechanisms controlling subtropical climate evolution across the last warm cycle. Here, we present new planktic foraminiferal assemblage data combined with δ18O values in surface and thermocline-dwelling foraminifera from the Bahamas, a region ideally suited to studying past changes in the subtropical ocean and atmosphere. Our data reveal that the peak sea surface warmth during early MIS 5e was intersected by an abrupt millennial-scale cooling/salinification event, which was possibly associated with a sudden southward displacement of the mean annual ITCZ position. This atmospheric shift is, in turn, ascribed to the transitional climatic regime of early MIS 5e, which was characterized by persistent ocean freshening in the high latitudes and an unstable AMOC mode.</p

Photoemission induced gating of topological insulator

The recently discovered topological insulators exhibit topologically protected metallic surface states which are interesting from the fundamental point of view and could be useful for various applications if an appropriate electronic gating can be realized. Our photoemission study of Cu intercalated Bi2Se3 shows that the surface states occupancy in this material can be tuned by changing the photon energy and understood as a photoemission induced gating effect. Our finding provides an effective tool to investigate the new physics coming from the topological surface states and suggests the intercalation as a recipe for synthesis of the material suitable for electronic applications.Comment: + resistivity data and some discussio

Combinatorial identities for binary necklaces from exact ray-splitting trace formulae

Based on an exact trace formula for a one-dimensional ray-splitting system, we derive novel combinatorial identities for cyclic binary sequences (P\'olya necklaces).Comment: 15 page

Green's function for the Relativistic Coulomb System via Sum Over Perturbation Series

We evaluate the Green's function of the D-dimensional relativistic Coulomb system via sum over perturbation series which is obtained by expanding the exponential containing the potential term $V({\bf x)}$ in the path integral into a power series. The energy spectra and wave functions are extracted from the resulting amplitude.Comment: 13 pages, ReVTeX, no figure

Interplay between Static and Dynamic Properties of Semifluxons in YBa2Cu3O7−δ 0−π Josephson Junctions

We have investigated the static and dynamic properties of long YBa2Cu3O7-delta 0-pi Josephson junctions and compared them with those of conventional 0 junctions. Scanning SQUID microscope imaging has revealed the presence of a semifluxon at the phase discontinuity point in 0-pi Josephson junctions. Zero field steps have been detected in the current-voltage characteristics of all junctions. Comparison with simulation allows us to attribute these steps to fluxons traveling in the junction for conventional 0 junctions and to fluxon-semifluxon interactions in the case of 0-pi Josephson junctions