Physicists have demonstrated a system in which light is used to control the motion of an object that is large enough to be seen with the naked eye at the level where quantum mechanics governs its behaviour.
The movement of objects is ultimately governed by the laws of quantum mechanics, which predict some intriguing phenomena: An object could simultaneously be in two places at the same time, and it should always be moving a little, even at a temperature of absolute zero – the oscillator is then said to be in its quantum ‘ground state’. Until recently, these strange predictions of quantum mechanics have only been observed in the motion of tiny objects such as individual atoms. For large objects, the unavoidable coupling of the object to the surrounding environment quickly washes out the quantum properties, in a process known as decoherence. But researchers in EPFL’s Laboratory of Photonics and Quantum Measurements have now shown that it is possible to use light to control the vibrational motion of a large object, consisting of a hundred trillion atoms, at the quantum level. The results of their research have been published in the February 2nd edition of Nature magazine.
The object they used was circular in design – a 30-micrometer diameter glass donut mounted on a microchip. Under the direction of Tobias Kippenberg, the team injected a laser into a thin optical fiber, and brought the fiber close to the donut, allowing light to ‘jump’ to the object and circulate around the circumference of the donut up to a million times. Just as the pressure of a finger running along the rim of a wineglass will cause it to hum, the tiny force exerted by the photons traveling inside the glass ring can cause it to vibrate at a well-defined frequency. But the force can in fact also dampen the vibrations, and thus cool down the oscillatory motion.