A Nanoparticle in a Laser Beam Feels Single Molecules Hit It

Yu-Han Tseng, David C. Moore and colleagues at Yale University and Lawrence Berkeley National Laboratory report that they have detected the momentum transferred by single gas molecules as they strike a nanoparticle held in a laser beam, one collision at a time. The measurement was published Oct. 19, 2026.

The group writes that counting those individual hits measures the pressure of the gas directly, and presents the result as a proof of principle for a pressure sensor built on single collisions. The authors also write that the sensitivity reached is what precision measurements of fundamental particle interactions would require. Both are stated as prospects, not as instruments already built. The paper appears in Physical Review Letters.

The particle is held in place by light alone, with no physical support. Three gases were used: krypton, xenon and sulfur hexafluoride. The authors report good agreement with theoretical expectations. They say the rate of detected events accurately measures each gas's own share of the pressure, its partial pressure. The shape of the spectrum they measure, they add, is a sensitive probe of the nanoparticle's surface, including its temperature.

The smallest impulse signal the group reconstructed was 200 keV/c, a momentum unit used in particle physics: an energy in thousands of electron volts divided by the speed of light.