“This is the culminating result,” says NIST physicist Julia Scherschligt. “We have had numerous positive developments before. But this validates the fact that our cold atom standard is truly a standard.”
When the CAVS sensor is connected to a vacuum chamber, the leftover atoms or molecules in the chamber collide with the trapped atoms. Each collision knocks an atom out of the trap, reducing the number of atoms and the intensity of light emitted. That intensity, easily measured by light sensors, serves as a sensitive measure of pressure. This relationship between the rate of dimming and the number of molecules is predicted exactly by quantum mechanics.
Published Aug. 10, 2023, in NIST News.
To verify the accuracy of their cold atom vacuum standard (CAVS) for measuring ultralow vacuum pressures, NIST researchers built a high-performance version of a traditional pressure metrology setup known as a dynamic expansion system. In this system, they injected gas at a flow rate of roughly 10 billion to 100 billion molecules per second into the top chamber. The gas moves from the upper chamber to the lower chamber, which is evacuated by a large pump at a known rate through a precisely dimensioned orifice. A set of gauges measured the pressure ratio between the top and bottom chambers to correct for imperfections. Using the gas inflow rate and the rate that gas moves between the two chambers, the researchers calculated the pressure in the top chamber, which the CAVS independently measures. The researchers found agreement between this known pressure value and the readings from the CAVS sensors, thereby validating their new method. Credit: NIST.
However, someone has to pay for this content. And that’s where advertising comes in. Most people consider ads a nuisance, but they do serve a useful function besides allowing media companies to stay afloat. They keep you aware of new products and services relevant to your industry. All ads in Quality Digest apply directly to products and services that most of our readers need. You won’t see automobile or health supplement ads.
“Indeed, the portable version is so simple, we eventually decided to automate it such that we very rarely had to intervene in its operation,” says NIST physicist Dan Barker. “In fact, most of the data from the portable CAVS for this study were taken while we were comfortably asleep at home.”
A vacuum chamber is never perfectly empty. A small number of atoms or molecules always remains, and measuring the tiny pressures they exert is critical. For instance, semiconductor manufacturers create microchips in vacuum chambers that must be almost entirely devoid of atomic and molecular contaminants, and so they need to monitor the gas pressure in the chamber to ensure that the contaminant levels are acceptably low.
Not only can CAVS make measurements as good as those in traditional pressure gauges, but it can also reliably measure the much lower vacuum pressures—a trillionth of the Earth’s sea-level atmospheric pressure and below—that will be required for future chip manufacturing and next-generation science. And its operation, based on well-understood quantum physics principles, means that it can make accurate readings “right out of the box” without requiring any adjustments or calibration to other reference pressure sources or techniques.
In this experiment, the researchers built a high-performance dynamic expansion system that allowed for extremely small flows of gas—in the range of 10 billion to 100 billion atoms or molecules per second—and included a custom-built flowmeter to measure flows that low. The hole they built to remove atoms slowly from the chamber was machined to submicrometer precision.
NIST researchers Dan Barker, Steve Eckel, Jim Fedchak, Julia Scherschligt, and their colleagues developed and tested a new method, known as the cold atom vacuum standard (CAVS), for measuring ultralow pressures. Credit: NIST.
Together, these CAVS systems promise to help researchers working with ultralow pressures reach new highs in both science and technology.
Dynamic expansion systems work by injecting a known amount of gas, measured in molecules per second, into a vacuum chamber, then slowly removing the gas from the other end of the chamber at a known rate. The researchers then calculate the resulting pressure in the chamber.
NIST Demonstrates New ‘Primary Standard’ for Measuring Ultralow Pressures
Chip manufacturing, gravitational wave detectors, and quantum computers could all benefit
Paper: Daniel S. Barker, James A. Fedchak, Jacek Kłos, Julia Scherschligt, Abrar A. Sheikh, Eite Tiesinga and Stephen P. Eckel. “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. Published online Aug. 1, 2023. DOI: 10.1116/5.0147686
NIST researcher Dan Barker checks on the CAVS setup in the lab. Credit: NIST.
“The heavy lifting needed to stand up to one of these classical standard devices is monumental,” Scherschligt said. “Going through the effort of doing that really drove home the point of this whole experiment, which is that CAVS provides high accuracy in a much simpler form.”
Published: Tuesday, August 29, 2023 – 12:02