Squeezing Light Cools Microscopic Drum Below Quantum Limit

Using a special circuit to generate microwave photons stripped of intensity fluctuations, physicists at the National Institute of Standards and Technology (NIST) have cooled a mechanical object to a temperature lower than previously thought possible.

NIST researchers applied a special form of microwave light to cool a microscopic aluminum drum to an energy level below the generally accepted limit, to just one fifth of a single quantum of energy. The drum, which is 20 micrometers in diameter and 100 nanometers thick, beat 10 million times per second while its range of motion fell to nearly zero. Courtesy of Teufel/NIST.

The new NIST theory and experiments showed that a microscopic mechanical drum — a vibrating aluminum membrane — could be cooled to less than one-fifth of a single quantum, or packet of energy.

John Teufel, the NIST physicist who led the experiment, said the new technique could be used to cool objects to absolute zero, the temperature at which matter is devoid of nearly all energy and motion.

"The colder you can get the drum, the better it is for any application," said Teufel. "Sensors would become more sensitive. You can store information longer. If you were using it in a quantum computer, then you would compute without distortion, and you would actually get the answer you want."

The drum, 20 micrometers in diameter and 100 nanometers thick, was embedded in a superconducting circuit designed so that the drum motion influenced the microwaves bouncing inside a hollow enclosure known as an electromagnetic cavity.

The NIST experiment used the "squeezed light" to drive the drum circuit, ultimately moving the noise and unwanted fluctuations from a useful property of the light to another aspect that doesn’t affect the experiment.

"Noise gives random kicks or heating to the thing you're trying to cool," Teufel said. "We are squeezing the light at a 'magic' level — in a very specific direction and amount — to make perfectly correlated photons with more stable intensity. These photons are both fragile and powerful."

The NIST theory and experiments indicate that squeezed light removes the generally accepted cooling limit; this includes objects that are large or operate at low frequencies, which are the most difficult to cool.

The drum might be used in applications such as hybrid quantum computers combining both quantum and mechanical elements.

The NIST study has been published in the journal Nature (doi:10.1038/nature20604).