A team of researches at the University of St Andrews in Scotland claim to have made the fastest spinning object to date — a birefringent crystalline vaterite sphere 4.4 μm in diameter (one fifteenth the diameter of a human hair) spun with circular polarized light to a peak rotational frequency of ten million rotations per second. (A wash machine on spin cycle makes about twenty rotations per second, for comparison.)
Vaterite is a polymorph of calcium carbonate (CaCO3), but one that I never heard of before. Some more familiar polymorphs of CaCO3 are calcite (the mineral that makes up limestone) and aragonite (the mineral that mollusks use to build their shells). Vaterite, calcite, and aragonite are birefringent, which means that light rays will follow two slightly different paths through these transparent materials.
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The spheres they manufactured are so small that they can be held in place and then spun with the pressure of laser light. The spinning was accomplished using circular polarized light — essentially light that spins. Something about the birefringence of the vaterite gives the circular polarized light something to grab onto. Pump out the air to reduce the drag and let the fun begin.
AnimateAn initial rotation rate of 110 Hz is recorded at atmospheric pressure, which increases to a stable rotation rate of 5 MHz for a pressure of 0.1 Pa. Decreasing the pressure further can lead to rotation rates of up to 10 MHz, although, at such rates, the particle is lost in a short period of time. We remark that this represents, to date, the largest measured rotation rate for a ‘man-made’ object.
The title for fastest rotating object was previously held by a flake of graphene (a single atom thick layer of graphite) suspended in an electric field and spun at something greater than 1 MHz. This article is hidden behind a paywall, but there’s a free copy at arXiv.org and a nice little summary at phys.org.