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Julia Scherschligt

Publications and source records attributed to Julia Scherschligt.

12 recordsLinked to original sources
arXiv2024

Compact Blackbody Radiation Atomic Sensor: Measuring Temperature using Optically Excited Atoms in Vapor Cells

We demonstrate a blackbody radiation thermometer based on optically excited rubidium atoms in a vapor cell. The temperature measurement is fast, with statistical uncertainty as low as 0.1% in one second. We resolve temperature with a precision of 0.04% in the range 308 K to 344 K when averaging for several seconds. Additionally, we describe an extension to this measurement scheme where the device operates as a self-calibrated, or primary, thermometer. We make progress toward realizing a primary thermometer by demonstrating a temperature-dependent self-consistent calibration scheme, with temperature accuracy of order 1% limited by the uncertainty in atomic transition dipole matrix elements.

physics.atom-ph↗
arXiv2024

On the effect of "glancing" collisions in the cold atom vacuum standard

We theoretically investigate the effect of ``glancing" collisions on the ultra-high vacuum (UHV) pressure readings of the cold atom vacuum standard (CAVS), based on either ultracold $^7$Li or $^{87}$Rb atoms. Here, glancing collisions are those collisions between ultracold atoms and room-temperature background atoms or molecules in the vacuum that do not impart enough kinetic energy to eject an ultracold atom from its trap. Our model is wholly probabilistic and shows that the number of the ultracold atoms remaining in the trap as a function of time is non-exponential. We update the recent results of a comparison between a traditional pressure standard -- a combined flowmeter and dynamic expansion system -- to the CAVS [D.S. Barker, et al., arXiv:2302.12143] to reflect the results of our model. We find that the effect of glancing collisions shifts the theoretical predictions of the total loss rate coefficients for $^7$Li colliding with noble gases or N$_2$ by up to $0.6$ %. Likewise, we find that in the limit of zero trap depth the experimentally extracted loss rate coefficients for $^{87}$Rb colliding with noble gases or N$_2$ shift by as much as 2.2 %.

physics.atom-ph↗
arXiv2023

Accurate measurement of the loss rate of cold atoms due to background gas collisions for the quantum-based cold atom vacuum standard

We present measurements of thermalized collisional rate coefficients for ultra-cold $^7$Li and $^{87}$Rb colliding with room-temperature He, Ne, N$_2$, Ar, Kr, and Xe. In our experiments, a combined flowmeter and dynamic expansion system, a vacuum metrology standard, is used to set a known number density for the room-temperature background gas in the vicinity of the magnetically trapped $^7$Li or $^{87}$Rb clouds. Each collision with a background atom or molecule removes a $^7$Li or $^{87}$Rb atom from its trap and the change in the atom loss rate with background gas density is used to determine the thermalized loss rate coefficients with fractional standard uncertainties better than 1.6 % for $^7$Li and 2.7 % for $^{87}$Rb. We find consistency -- a degree of equivalence of less than one -- between the measurements and recent quantum-scattering calculations of the loss rate coefficients [J. Klos and E. Tiesinga, J. Chem. Phys. 158, 014308 (2023)], with the exception of the loss rate coefficient for both $^7$Li and $^{87}$Rb colliding with Ar. Nevertheless, the agreement between theory and experiment for all other studied systems provides validation that a quantum-based measurement of vacuum pressure using cold atoms also serves as a primary standard for vacuum pressure, which we refer to as the cold-atom vacuum standard.

physics.atom-ph↗
arXiv2022

Comparison of two multiplexed portable cold-atom vacuum standards

We compare the vacuum measured by two portable cold-atom vacuum standards (pCAVS) based on ultracold $^7$Li atoms. The pCAVS are quantum-based standards that use a priori scattering calculations to convert a measured loss rate of cold atoms from a conservative trap into a background gas pressure. Our pCAVS devices share the same laser system and measure the vacuum concurrently. The two pCAVS together detected a leak with a rate on the order of $10^{-6}$ Pa L/s. After fixing the leak, the pCAVS measured a pressure of about 40 nPa with 2.6 % uncertainty. The two pCAVS agree within their uncertainties, even when swapping some of their component parts. Operation of the pCAVS was found to cause some additional outgassing, on the order of $10^{-8}$ Pa L/s, which can be mitigated in the future by better thermal management.

physics.atom-ph↗
arXiv2021

Stability of bakeable capacitance diaphragm gauges

Here, we study the stability of capacitance diaphragm gauges. We focus on their stability before and after a controlled series of bakes. We find that baking results in appreciable shifts of the zero offset, but note that these can easily be corrected at time of use. Linearity however cannor be corrected at time of use, so it is essential to understand its effect if one wished to use similar gauges in a system that requires baking. For the gauges in this study, we find that baking introduces a minimal additional uncertainty, and that the total uncertainty can be kept to below about 0.3% at the k=2 confidence level (95%).

physics.ins-det↗
arXiv2018

Nuclear-Spin Dependent Parity Violation in Optically Trapped Polyatomic Molecules

We investigate using optically trapped linear polyatomic molecules as probes of nuclear spin-dependent parity violation. The presence of closely spaced, opposite-parity $\ell$-doublets is a general feature of such molecules, allowing parity-violation-sensitive pairs of levels to be brought to degeneracy in magnetic fields typically 100 times smaller than in diatomics. Assuming laser cooling and trapping of polyatomics at the current state-of-the-art for diatomics, we expect to measure nuclear spin-dependent parity-violating matrix elements $iW$ with 70 times better sensitivity than the current best measurements. Our scheme should allow for 10 \% measurements of $iW$ in nuclei as light as Be or as heavy as Yb, with averaging times on order the of 10 days and 1 second, respectively.

physics.atom-ph↗
arXiv2018

Challenges to miniaturizing cold atom technology for deployable vacuum metrology

Cold atoms are excellent metrological tools; they currently realize SI time and, soon, SI pressure in the ultra-high (UHV) and extreme high vacuum (XHV) regimes. The development of primary, vacuum metrology based on cold atoms currently falls under the purview of national metrology institutes. Under the emerging paradigm of the "quantum-SI", these technologies become deployable (relatively easy-to-use sensors that integrate with other vacuum chambers), providing a primary realization of the pascal in the UHV and XHV for the end-user. Here, we discuss the challenges that this goal presents. We investigate, for two different modes of operation, the expected corrections to the ideal cold-atom vacuum gauge and estimate the associated uncertainties. Finally, we discuss the appropriate choice of sensor atom, the light Li atom rather than the heavier Rb.

physics.atom-ph↗
arXiv2018

Quantum-based vacuum metrology at NIST

The measurement science in realizing and disseminating the unit for pressure in the International System of Units (SI), the pascal (Pa), has been the subject of much interest at the National Institute of Standards and Technology (NIST). Modern optical-based techniques for pascal metrology have been investigated, including multi-photon ionization and cavity ringdown spectroscopy. Work is ongoing to recast the pascal in terms of quantum properties and fundamental constants and in so doing, make vacuum metrology consistent with the global trend toward quantum-based metrology. NIST has ongoing projects that interrogate the index of refraction of a gas using an optical cavity for low vacuum, and count background particles in high vacuum to extreme high vacuum using trapped laser-cooled atoms.

physics.ins-det↗
arXiv2018

Development of a new UHV/XHV pressure standard (cold atom vacuum standard)

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.

physics.app-ph↗
arXiv2018

A 3D-printed alkali metal dispenser

We demonstrate and characterize a source of Li atoms made from direct metal laser sintered titanium. The source's outgassing rate is measured to be $5 \,(2)\cdot 10^{-7}$\,$\rm{Pa}~ \rm{L}~ \rm{s}^{-1}$ at a temperature $T=330\,^\circ$C, which optimizes the number of atoms loaded into a magneto-optical trap. The source loads $\approx 10^7$ $^7$Li atoms in the trap in $\approx 1$\,s. The loaded source weighs 700\,mg and is suitable for a number of deployable sensors based on cold atoms.

physics.ins-det↗
arXiv2002

Anisotropic Magnetoresistance in Ga$_{1-x}$Mn$_x$As

We have measured the magnetoresistance in a series of Ga$_{1-x}$Mn$_x$As samples with 0.033$\le x \le$ 0.053 for three mutually orthogonal orientations of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in these materials is negative (i.e. the sample resistance is higher when its magnetization is perpendicular to the measuring current than when the two are parallel) and has a magnitude on the order of 5% at temperatures near 10K and below. This stands in contrast to the results for most conventional magnetic materials where the SRA is considerably smaller in magnitude for those few cases in which a negative sign is observed. The magnitude of the SRA drops from its maximum at low temperatures to zero at T$_C$ in a manner that is consistent with mean field theory. These results should provide a significant test for emerging theories of transport in this new class of materials.

cond-mat.mtrl-sci↗