In a milestone for quantum optomechanics, researchers at ETH Zurich have trapped a cluster of three nano glass spheres, smaller than a human hair, in a laser-based optical tweezer and cooled their rotational motion to within 8 percent of classical noise at room temperature.
This platform makes it possible to build practical quantum devices, such as ultra-sensitive force sensors, navigation systems that work without GPS, and advanced medical imagers, that can operate in standard laboratory or clinical settings without bulky cryogenic equipment.
By suppressing external disturbances and implementing active phase-noise cancellation, they observed the object’s zero-point fluctuations, or intrinsic “trembling”, with 92 percent of its motion attributed to genuine quantum effects. This achievement marks the highest quantum state purity for a mechanically levitated object without cryogenics and paves the way toward real-world quantum technologies.
Background and Significance
Quantum researchers traditionally rely on cooling systems near absolute zero to suppress thermal noise. In contrast, Martin Frimmer’s group used coherent scattering into a high-finesse Fabry–Pérot cavity to cool the megahertz-frequency librational mode of an optically levitated silica nanoparticle cluster from room temperature to its quantum ground state.
Key Findings
- Levitated cluster diameter ten times smaller than a human hair remained motionless in three dimensions
- Rotational oscillations measured at one million deflections per second revealed zero-point fluctuations
- Sideband thermometry inferred a phonon population of 0.04 quanta, corresponding to 92 percent quantum purity
- Active phase-noise cancellation achieved up to 20 dB suppression of laser fluctuations
- No cryogenic cooling required, simplifying future device integration
How Did They Do It?
The experiment placed the anisotropic nanosphere cluster in an ultrahigh vacuum chamber and focused polarized laser light through a high-numerical-aperture lens to form an optical tweezer. At the focal point, the particle’s long axis aligned with the electric field, creating a stable trapping potential. Coherent scattering into a Fabry–Pérot cavity enhanced anti-Stokes processes, extracting energy from the librational motion. Meanwhile, a Mach–Zehnder-based phase-noise eater reduced laser phase noise, allowing the team to approach the quantum back-action limit.
Why Does This Matter?
Imagine sensors that detect the tiniest forces—from individual gas molecules to elusive dark matter interactions—without freezing components to near absolute zero. Or navigation tools that remain accurate underground or underwater where GPS cannot reach. In medicine, room-temperature quantum sensors could pick up faint biomagnetic signals, improving diagnostics for heart and brain health.
Looking Ahead
With this “perfect start”, as Frimmer describes it, the next steps include squeezing the high-purity librational mode, extending phase-noise suppression to other mechanical degrees of freedom, and integrating levitated particles with atomic qubits. Such advances will deepen our understanding of gravity’s role in quantum mechanics and drive the development of real-world quantum technologies.
Journal: Nature Physics
DOI: 10.1038/s41567-025-02976-9
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