



01669nas a2200181   4500008004100000245010700041210006900148260001300217490000800230520098500238100002701223700002201250700002201272700002401294700001901318700001901337856013101356       2020                        eng d00aCollisions of room-temperature helium with ultracold lithium and the van der Waals bound state of HeLi0 aCollisions of roomtemperature helium with ultracold lithium and   c1/6/20200 v1013 a<p>We have computed the thermally averaged total, elastic rate coefficient for the collision of a room-temperature helium atom with an ultracold lithium atom. This rate coefficient has been computed as part of the characterization of a cold-atom vacuum sensor based on laser-cooled Li 6 or Li 7 atoms that will operate in the ultrahigh-vacuum (p&lt; 10&minus; 6 Pa) and extreme-high-vacuum (p&lt; 10&minus; 10 Pa) regimes. The analysis involves computing the X 2 Σ+ HeLi Born-Oppenheimer potential followed by the numerical solution of the relevant radial Schrödinger equation. The potential is computed using a single-reference-coupled-cluster electronic-structure method with basis sets of different completeness in order to characterize our uncertainty budget. We predict that the rate coefficient for a 300 K helium gas and a 1 μ K Li gas is 1.467 (13)&times; 10&minus; 9 cm 3/s for He 4+ Li 6 and 1.471 (13)&times; 10&minus; 9 cm 3/s for He 4+ Li 7, where the &hellip;</p>1 aMakrides, Constantinos1 aBarker, Daniel, S1 aFedchak, James, A1 aScherschligt, Julia1 aEckel, Stephen1 aTiesinga, Eite  uhttps://www.quics.umd.edu/publications/collisions-room-temperature-helium-ultracold-lithium-and-van-der-waals-bound-state-heli01586nas a2200193   4500008004100000245007900041210006900120260001400189490000700203520099200210100002401202700002201226700002201248700001901270700002001289700002701309700001901336856003701355       2017                        eng d00aDevelopment of a new UHV/XHV pressure standard (cold atom vacuum standard)0 aDevelopment of a new UHVXHV pressure standard cold atom vacuum s  c2017/11/30 v543 a<p>The National Institute of Standards and Technology has recently begun a program to develop a primary pressure standard that is based on ultra-cold atoms, covering a pressure range of 1 x 10-6 to 1 x 10-10 Pa and possibly lower. These pressures correspond to the entire ultra-high vacuum range and extend into the extreme-high vacuum. This cold-atom vacuum standard (CAVS) is both a primary standard and absolute sensor of vacuum. The CAVS is based on the loss of cold, sensor atoms (such as the alkali-metal lithium) from a magnetic trap due to collisions with the background gas (primarily H2) in the vacuum. The pressure is determined from a thermally-averaged collision cross section, which is a fundamental atomic property, and the measured loss rate. The CAVS is primary because it will use collision cross sections determined from ab initio calculations for the Li + H2 system. Primary traceability is transferred to other systems of interest using sensitivity coefficients.</p>1 aScherschligt, Julia1 aFedchak, James, A1 aBarker, Daniel, S1 aEckel, Stephen1 aKlimov, Nikolai1 aMakrides, Constantinos1 aTiesinga, Eite  uhttps://arxiv.org/abs/1801.1012001945nas a2200205   4500008004100000245007600041210006900117260001500186300001100201490000700212520133700219100001901556700001901575700001901594700002401613700002701637700001801664700001901682856003801701       2015                        eng d00aSelf-heterodyne detection of the {\it in-situ} phase of an atomic-SQUID0 aSelfheterodyne detection of the it insitu phase of an atomicSQUI  c2015/09/03  a0336020 v923 a  We present theoretical and experimental analysis of an interferometric
measurement of the {\it in-situ} phase drop across and current flow through a
rotating barrier in a toroidal Bose-Einstein condensate (BEC). This experiment
is the atomic analog of the rf-superconducting quantum interference device
(SQUID). The phase drop is extracted from a spiral-shaped density profile
created by the spatial interference of the expanding toroidal BEC and a
reference BEC after release from all trapping potentials. We characterize the
interferometer when it contains a single particle, which is initially in a
coherent superposition of a torus and reference state, as well as when it
contains a many-body state in the mean-field approximation. The single-particle
picture is sufficient to explain the origin of the spirals, to relate the
phase-drop across the barrier to the geometry of a spiral, and to bound the
expansion times for which the {\it in-situ} phase can be accurately determined.
Mean-field estimates and numerical simulations show that the inter-atomic
interactions shorten the expansion time scales compared to the single-particle
case. Finally, we compare the mean-field simulations with our experimental data
and confirm that the interferometer indeed accurately measures the {\it
in-situ} phase drop.
1 aMathew, Ranchu1 aKumar, Avinash1 aEckel, Stephen1 aJendrzejewski, Fred1 aCampbell, Gretchen, K.1 aEdwards, Mark1 aTiesinga, Eite  uhttp://arxiv.org/abs/1506.09149v2