Light tends to heat things up; less obvious are its dramatic cooling capabilities. Now it seems light's cold side could provide a cheaper, easier way to explore the limits of quantum theory.

Quantum mechanics describes the behaviour of electrons and atoms, but not everyday "macroscopic" objects. One way to probe where and why quantum laws break down is to induce quantum behaviour in ever-larger objects. At room temperature, thermal vibrations destroy delicate quantum states. So the largest object to attain a quantum state, a microscopic lever in a "superposition" of still and vibrating states, was cooled cryogenically to 25 millikelvin.

As cryogenics are expensive and tricky to use, a team led by Oskar Painter of the California Institute of Technology in Pasadena etched a pattern onto a silicon strip about 15 micrometres long. This allowed it to trap light, as well as mechanical vibrations due to heat, but only at certain, resonant frequencies.

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