Measuring the Emptiness of a Vacuum
Stephen Eckel
Group Leader, Fundamental Thermodynamics Group
Sensor Sciences Division
NIST
About the Lecture
From the tiniest semiconductors manufactured to underpin the AI revolution to the detection of ripples of spacetime due to coalescing black holes, modern technologies and discoveries rely on some of the purest vacuums obtainable on Earth. These vacuums are so pure, that for every gas molecule left behind in the vacuum chamber, roughly 100 billion have been removed. At such ultra-high vacuum pressures, the current best way to measure pressure is the so-called ionization gauge, invented during the vacuum tube era. Unreliable and inaccurate at best, ionization gauges require constant recalibration to be used in any application requiring even modest accuracy.
At NIST, we are endeavoring to change the way vacuum is measured in the ultra-high and extreme-high vacuum regimes by utilizing techniques from modern atomic physics. Our technique requires laser cooling and trapping clouds of roughly 100,000 lithium or rubidium atoms and suspending them in a trap formed by magnetic fields within the vacuum chamber whose pressure we wish to measure. The atom clouds are cold, roughly 100 millionths of a degree above absolute zero, and the traps holding them are just strong enough to confine these barely moving atoms. If a left-behind gas molecule bouncing around the vacuum chamber strikes one of the laser-cooled atoms, it will, with near unity probability, eject the atom from the trap. Thus, one can use the measured loss rate of atoms from the trap together with the calculated cross-section for a collision to extract the vacuum pressure.
Over the last decade, we have built several devices – called cold-atom vacuum standards (CAVSs) – based on this measurement principle. In the last several years, we have verified the technique and the quantum mechanical calculations that underpin it using laboratory-scale devices. In parallel, we also developed a version that can act as a replacement for the crude ionization gauges used today, which we call the portable cold-atom vacuum standard (p-CAVS). As we look toward the future, we continue to refine our prototype p-CAVS, so that it can be used in industry and science as a drop-in replacement for ionization gauges and be ready to deliver the accuracy needed for when the next generation of advanced manufacturing or big science experiments requires even better vacuums.
Selected Reading & Media References
Popular Science (https://www.popsci.com/science/vacuum-measurements-manufacturing-new-method/)
Popular Mechanics (https://www.popularmechanics.com/science/a44904905/new-way-to-measure-nothing/)
Physics World (https://physicsworld.com/a/cold-atoms-used-to-create-reliable-pressure-gauge-for-ultra-high-vacuum/)
IEEE Spectrum (https://spectrum.ieee.org/vacuum-measurement)
NIST press releases:
https://www.nist.gov/news-events/news/2023/08/nist-demonstrates-new-primary-standard-measuring-ultralow-pressures
https://www.nist.gov/news-events/news/2022/07/primary-standard-measuring-vacuum
About the Speaker
Stephen Eckel is the Group Leader of the Fundamental Thermodynamics Group at the National Institute of Standards and Technology (NIST). Previously at NIST he served as research physicist developing quantum-based, cold-atom measurement standards.
Stephen’s research centers on cold-atom sensing and precision measurement, particularly the use of atoms and molecules to create calibration-free sensors for pressure/vacuum and temperature. A major focus of his work is translating quantum systems—laser-cooled atoms, atom–molecule interactions, and precision spectroscopy—into practical metrology tools that can function as primary standards and deployable instruments.
He was a member of the team that developed the cold atom vacuum standard, currently the only primary standard of vacuum pressure in the ultra-high and extreme-high vacuum regimes. And Stephen and collaborators demonstrated the portable Cold Atom Vacuum Standard (pCAVS), a first-of-its-kind absolute vacuum standard and quantum-mechanical vacuum pressure sensor.
Stephen is an author on more than 56 scientific and technical publications and an inventor in six patent applications and patents.
Among other honors and awards, Stephen is a recipient of the Presidential Early Career Award for Scientists and Engineers, a Department of Commerce Bronze Medal for the pCAVS demonstration, and the Physical Measurement Laboratory’s Scientific Leadership Award.
He earned a B.S. in Physics at Lehigh University and a Ph.D. in Physics at Yale.
Google Scholar: https://scholar.google.com/citations?hl=en&user=WrHKnoAAAAAJ
ResearchGate: https://www.researchgate.net/profile/Stephen-Eckel?ev=prf_overview
Webpage(s): https://www.nist.gov/people/stephen-eckel