Scientists have managed to cool a mechanical object to temperatures lower than previously thought possible suggesting that theoretically it is possible to cool objects to absolute zero temperature.
The experiment was conducted by scientists on a mechanical aluminium drum measuring 20 micrometers in diameter and 100 nanometers thick. The drum was embedded in a superconducting circuit designed so that the drum motion influences the microwaves – a form of electromagnetic radiation – bouncing inside a hollow enclosure known as an electromagnetic cavity.
Scientists published their findings in journal Nature wherein they showed that the vibrating aluminum membrane could be cooled to less than one-fifth of a single quantum, or packet of energy, lower than ordinarily predicted by quantum physics. Scientists added that their new technique paves way, theoretically, for cooling of objects to absolute zero.
The technique makes use of “squeezed light” to drive the drum circuit. Squeezing is a quantum mechanical concept in which noise, or unwanted fluctuations, is moved from a useful property of the light to another aspect that doesn’t affect the experiment. These quantum fluctuations limit the lowest temperatures that can be reached with conventional cooling techniques. The NIST team used a special circuit to generate microwave photons that were purified or stripped of intensity fluctuations, which reduced inadvertent heating of the drum.
In a previous experiment NIST scientists cooled the quantum drum to its lowest-energy “ground state,” or one-third of one quantum. They used a technique called sideband cooling, which involves applying a microwave tone to the circuit at a frequency below the cavity’s resonance. This tone drives electrical charge in the circuit to make the drum beat. The drumbeats generate light particles, or photons, which naturally match the higher resonance frequency of the cavity. These photons leak out of the cavity as it fills up. Each departing photon takes with it one mechanical unit of energy—one phonon—from the drum’s motion. This is the same idea as laser cooling of individual atoms, first demonstrated at NIST in 1978 and now widely used in applications such atomic clocks.