Nanorotor Cooled to 2D Quantum Ground State for First Time
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- University of Vienna researchers, with TU Wien and Ulm University, achieved the first 2D quantum ground state cooling of a nanorotor's rotation, as reported in Nature Physics.
- The nano-dumbbell rotor — two 150 nm silica spheres — was cooled via optical methods to a few tens of microkelvin above absolute zero, confining orientation to ~20 microradians of uncertainty.
- Lead author Stephan Troyer said the rotor's tip moves "less than one hundredth of the diameter of a single atom" — a level of orientation precision unattained in 2D before.
- Previous 1D rotational quantum cooling of a levitated nanoparticle came from Lukas Novotny's team at ETH Zürich; the new result extends quantum control to both orientational axes.
- The silica rotor comprises roughly 100 million atoms — orders of magnitude more massive than typical quantum test systems (single atoms, ions, or molecules), probing the quantum-classical boundary.
- When the trapping laser is switched off, the nanorotor can enter a quantum superposition of all orientations simultaneously; its initial alignment dissolves before reviving after a well-defined time, enabling rotational matter-wave interferometry.
- Researchers used coherent scattering cooling at 100 MW/cm² light intensity, with each scattered photon removing a single quantum of mechanical energy from the rotor's rotation.
Why it matters: The first 2D quantum ground state cooling of a 100-million-atom silica rotor enables rotational matter-wave interferometry and ultra-sensitive quantum torque detection, per the University of Vienna team. The technique scales to smaller particles — Troyer notes cooling works across sizes, targeting structures 100 times lighter for rotational quantum interference experiments.
