Pressure from Individual Particles Measured for the First Time

By VirentaNews Staff — May 17, 2026

For the first time in history, scientists have measured the minuscule pressure exerted by individual particles—a feat once thought impossible due to the vanishingly small forces involved. Using a microscopic silica bead suspended in a vacuum by a laser beam, researchers have created an ultra-sensitive optomechanical sensor capable of detecting quantum-scale radiation pressure. This pressure, equivalent to a few attonewtons (10^-18 newtons), arises when photons or other particles strike a surface. The experiment, conducted at the University of Vienna and published in Nature Physics, marks a turning point in quantum measurement science, offering a new way to probe fundamental particles and forces at previously inaccessible scales. Such precision could soon allow physicists to detect elusive phenomena, including the hypothetical Majorana neutrino, which may hold the key to understanding why the universe contains more matter than antimatter.

Why Quantum Pressure Measurement Matters Now

Until now, the forces generated by individual particles have been too faint to measure directly, hiding behind thermal noise and instrumental limitations. But advances in laser cooling, vacuum technology, and nanofabrication have converged to make such measurements feasible. The ability to detect radiation pressure at the single-particle level opens a new frontier in quantum optomechanics—the study of how light interacts with mechanical systems. This is not merely a technical achievement; it reshapes how scientists can test quantum mechanics in macroscopic systems. Moreover, with growing interest in dark matter, quantum gravity, and neutrino physics, tools that can sense the faintest interactions are urgently needed. This breakthrough arrives at a critical moment when theoretical predictions outpace experimental capabilities, and physicists are racing to build instruments sensitive enough to test them.

A Bead Suspended by Light Acts as a Quantum Force Sensor

The device at the heart of this discovery is deceptively simple: a 200-nanometer silica bead levitated in a high-vacuum chamber by a tightly focused laser beam—a technique known as optical trapping. The bead, isolated from nearly all environmental disturbances, behaves like a nearly perfect harmonic oscillator. When photons strike it, they impart tiny momentum kicks, causing measurable displacements. By monitoring these movements with interferometric precision, researchers can back-calculate the force exerted. In this experiment, the team achieved a sensitivity of 5 attonewtons per square root hertz, enabling them to detect pressure from just a few photons. Crucially, the system operates at room temperature, avoiding the need for complex cryogenic setups. The levitation method eliminates physical contact with supports, which would otherwise introduce noise and damping, making this one of the most isolated mechanical systems ever created.

Probing the Quantum Frontier with Unprecedented Sensitivity

The implications of this technology extend far beyond measuring photon pressure. The same sensor could be used to detect weakly interacting particles, such as the Majorana neutrino—a theoretical particle that is its own antiparticle. Unlike conventional neutrinos, Majorana neutrinos could explain the matter-antimatter asymmetry in the universe through a process called leptogenesis. Detecting them requires observing extremely rare, low-energy interactions, which this optomechanical system is uniquely suited to sense. Additionally, researchers suggest the device could test theories of wavefunction collapse, search for dark matter candidates like hidden photons, or even explore quantum gravity effects. Because the bead is macroscopic yet governed by quantum laws when cooled, it serves as a bridge between quantum and classical physics, allowing tests of quantum superposition at larger scales. According to lead researcher Uroš Delić, “We are pushing the boundaries of what can be measured, inching closer to observing quantum effects in objects visible to the naked eye.”

From Lab Experiment to Fundamental Physics Discoveries

This technology could transform how physicists search for new particles and forces. Traditional detectors, like those at CERN or neutrino observatories, rely on large-scale collisions or rare decays within tons of material. In contrast, this optomechanical approach offers a tabletop alternative with extreme sensitivity to weak, continuous forces. If refined, such sensors could be deployed in networks to detect dark matter waves or exotic fields permeating space. Moreover, because the system responds to momentum transfer rather than ionization or light emission, it is sensitive to particles that do not interact electromagnetically—precisely the kind that evade conventional detectors. Biomedical and materials science applications may also emerge, such as non-invasive probing of cellular mechanics or atomic-scale surface forces. However, the primary impact lies in fundamental physics, where even a single unexpected force signature could signal new physics beyond the Standard Model.

Expert Perspectives

“This experiment demonstrates a remarkable level of control over a mesoscopic object,” says Prof. Mark Kasevich, a quantum physicist at Stanford University who was not involved in the study. “It’s a major leap in force sensitivity.” Others caution that scaling the technology for particle detection will require reducing noise even further and improving particle interaction cross-sections. “The challenge isn’t just sensitivity—it’s knowing what you’re measuring,” notes Dr. Sabine Hossenfelder, a theoretical physicist at the Frankfurt Institute for Advanced Studies. While some experts see this as a path to new physics, others emphasize that distinguishing signal from noise at such scales remains a formidable hurdle. Still, there is broad agreement that levitated optomechanics is becoming a vital tool in the quantum arsenal.

Looking ahead, researchers aim to cool the bead to its quantum ground state and observe quantum superpositions of motion. They also plan to expose the sensor to controlled particle beams to calibrate its response. If successful, this could lead to a new class of quantum sensors capable of detecting particles no accelerator can produce. The next five years may see the first attempts to use such devices in searches for Majorana neutrinos or dark matter. As quantum measurement edges closer to the limits imposed by Heisenberg’s uncertainty principle, one question remains: what undiscovered forces are we now able to feel?

Source: New Scientist