@article { ISI:000505979700006,
title = {Collisions of room-temperature helium with ultracold lithium and the van der Waals bound state of HeLi},
journal = {Phys. Rev. A},
volume = {101},
number = {1},
year = {2020},
month = {JAN 6},
pages = {012702},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {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 < 10(-6) Pa) and extreme-high-vacuum (p < 10(-10) Pa) regimes. The analysis involves computing the X (2) Sigma(+) HeLi Born-Oppenheimer potential followed by the numerical solution of the relevant radial Schrodinger 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 mu K Li gas is 1.467(13) x 10(-9) cm(3)/s for He-4 + Li-6 and 1.471(13) x 10(-9) cm(3)/s for He-4 + Li-7, where the numbers in parentheses are the one-standard-deviation uncertainties in the last two significant digits. We quantify the temperature dependence as well. Finally, we evaluate the s-wave scattering length and binding of the single van der Waals bound state of HeLi. We predict that this weakly bound level has a binding energy of -0.0064(43) x hc cm(-1) and -0.0122(67) x hc cm(-1) for He-4 + Li-6 and He-4 + Li-7, respectively. The calculated binding energy of He-4 + Li-7 is consistent with the sole experimental determination.},
issn = {2469-9926},
doi = {10.1103/PhysRevA.101.012702},
author = {Makrides, Constantinos and Barker, Daniel S. and Fedchak, James A. and Scherschligt, Julia and Eckel, Stephen and Tiesinga, Eite}
}
@article {ISI:000466237600004,
title = {Elastic rate coefficients for Li+H-2 collisions in the calibration of a cold-atom vacuum standard},
journal = {Phys. Rev. A},
volume = {99},
number = {4},
year = {2019},
month = {APR 29},
pages = {042704},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {Ongoing efforts at the National Institute of Standards and Technology in creating a cold-atom vacuum standard device have prompted theoretical investigations of atom-molecule collision processes that characterize its operation. Such a device will operate as a primary standard for the ultrahigh-vacuum and extreme-high-vacuum regimes. This device operates by relating loss of ultracold lithium atoms from a conservative trap by collisions with ambient atoms and molecules to the background density and thus pressure through the ideal gas law. The predominant background constituent in these environments is molecular hydrogen H-2. We compute the relevant Li+H-2 Born-Oppenheimer potential energy surface, paying special attention to its uncertainty. Coupled-channel calculations are then used to obtain total rate coefficients, which include momentum-changing elastic and inelastic processes. We find that inelastic rotational quenching of H-2 is negligible near room temperature. For a (T = 300)-K gas of H-2 and 1.0-mu K gas of Li atoms prepared in a single hyperfine state, the total rate coefficients are 6.0(1) x 10(-9) cm(3)/s for both Li-6 and Li-7 isotopes, where the number in parentheses corresponds to a one-standard-deviation combined statistical and systematic uncertainty. We find that a 10-K increase in the H-2 temperature leads to a 1.9\% increase in the rate coefficients for both isotopes. For Li temperatures up to 100 mu K, changes are negligible. Finally, a semiclassical Born approximation significantly overestimates the rate coefficients. The difference is at least ten times the uncertainty of the coupled-channel result.},
issn = {2469-9926},
doi = {10.1103/PhysRevA.99.042704},
author = {Makrides, Constantinos and Barker, Daniel S. and Fedchak, James A. and Scherschligt, Julia and Eckel, Stephen and Tiesinga, Eite}
}
@article { ISI:000444740400001,
title = {Challenges to miniaturizing cold atom technology for deployable vacuum metrology},
journal = {METROLOGIA},
volume = {55},
number = {5},
year = {2018},
month = {OCT},
pages = {S182-S193},
keywords = {cold atom sensing, quantum-SI, vacuum metrology},
issn = {0026-1394},
doi = {10.1088/1681-7575/aadbe4},
author = {Eckel, Stephen and Barker, Daniel S. and Fedchak, James A. and Klimov, Nikolai N. and Norrgard, Eric and Scherschligt, Julia and Makrides, Constantinos and Tiesinga, Eite}
}
@article { ISI:000414365000002,
title = {Development of a new UHV/XHV pressure standard (cold atom vacuum standard)},
journal = {METROLOGIA},
volume = {54},
number = {6},
year = {2017},
month = {DEC},
pages = {S125-S132},
issn = {0026-1394},
doi = {10.1088/1681-7575/aa8a7b},
author = {Scherschligt, Julia and Fedchak, James A. and Barker, Daniel S. and Eckel, Stephen and Klimov, Nikolai and Makrides, Constantinos and Tiesinga, Eite}
}