The NIST Fundamental Thermodynamics Group is seeking a motivated individual with a background in physics or mechanical engineering to work both in our cold atom vacuum standard (CAVS) lab. The CAVS is a vacuum gauge that works by measuring the loss rate of laser-cooled atoms from a conservative, magnetic trap due to collisions with gas molecules left behind in the vacuum chamber [1]. Specifically, samples of atoms are laser cooled in magneto-optical traps and subsequently loaded into a magnetic trap. After some time in the magnetic trap, the remaining atoms are recaptured into the magneto-optical trap and counted using fluorescence imaging. The resulting atom number versus time in the magnetic trap curves are fit to expontentials to extract the loss rate. Using a priori calculations of the collisional parameters between the background gas and sensor atoms, the exponential loss rate can be used to infer the gas density and, with the additional knowledge of the temperature, the gas pressure. Because the collisional parameters can be calculated a priori, the CAVS is a standard for vacuum pressure in ultra-high vacuum regime and below in addition to being a sensor. In 2022, our group compared two portable CAVS devices against each other and demonstrated that they agree with each other without caibration [2]. In 2023, we published a comparison between a portable CAVS using lithium sensor atoms, a laboratory-scale CAVS using rubidium sensor atoms, and a traditional vacuum metrology apparatus and found agreement between all three [3].

There are many outstanding questions left to answer about the CAVS. First, we do not know the lowest pressure at which the gauge can operate. Second, our current measurements at our lowest attainable pressures show super-exponential loss from the trap; we currently do not understand the physical mechanism for this additional loss [3]. Both of these outstanding questions can be answered though through a combination of upgrades to the apparatus, more experimental data, and simulation. The ideal postdoctoral researcher on the project should be able to do all three.

[1] Barker et al., “Precise Quantum Measurement of Vacuum with Cold Atoms.” Review of Scientific Instruments 93 121101 (2022).

[2] Ehinger et al., “Comparison of Two Multiplexed Portable Cold-Atom Vacuum Standards.” AVS Quantum Science 4 034403 (2022).

[3] Barker et al., “Accurate Measurement of the Loss Rate of Cold Atoms Due to Background Gas Collisions for the Quantum-Based Cold Atom Vacuum Standard.” AVS Quantum Science 5 035001 (2023).

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