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A tiny glass bead hangs in a laser beam like a speck of dust in sunlight. Around it is a rarefied gas: atoms of krypton, xenon, and heavy molecules of sulfur hexafluoride. They collide with the bead, and each hit transfers a tiny impulse, like a pea thrown at a taut sheet makes it tremble.

The authors of the study recorded these shifts and reconstructed the force of each individual hit. It turned out that the frequency of hits precisely indicates how much gas is around: count the hits — know the pressure. Also, from the nature of the trembling, the temperature of the bead's surface can be determined. The faintest nudges they could detect carry an impulse of just 200 kiloelectronvolts divided by the speed of light — trillions of times less than the impulse of a flying mosquito.

Such a sensitive "nanobarometer" could become a new standard for measuring pressure in vacuum — without mercury columns or membranes, simply by counting molecular hits. And in the future, such levitating sensors could help study how particles interact with each other at the smallest distances.

Original abstract

as written by the authors arXiv:2604.18371

We experimentally demonstrate the detection of momentum transfers from individual collisions of Kr, Xe, and SF$$_6$$ with an optically levitated nanoparticle, finding good agreement with theoretical expectations. The observed event rates accurately measure the gas partial pressures, while the spectral shape provides a sensitive probe of the surface properties of the nanoparticle, including its temperature. The reconstruction of impulse signals as small as 200 keV/$$c$$ further establishes that levitated optomechanical sensors can reach the sensitivity required for precision measurements of fundamental particle interactions, and demonstrates a proof-of-principle for a primary pressure sensor based on the detection of individual gas particle collisions.