It’s the coolest drum of all time. The temperature of a tiny round membrane, only 20 micrometers wide and 100 nanometers thick, has been lowered below the “quantum limit”, colder than was thought possible.
The usual way to get something to an extraordinarily cold temperature is to use laser cooling, in which highly organised light dampens the thermal vibrations by slowing the random motion of atoms. The more organised the light, the more effectively it can cool things.
A new technique developed by a team at the National Institute of Standards and Technology in Boulder, Colorado, uses “squeezed” light to get atoms colder than is possible with regular laser cooling.
Squeezed light is more organised in one particular orientation and less in others. It has been used in other contexts before, but never for cooling. “This research combines several fields that have existed for quite some time, so it’s kind of surprising that no one tried to do this experiment before,” says Amir Safavi-Naeini at Stanford University in California, who was not involved in the research.
By shining squeezed light on a thin aluminium membrane resembling the head of a snare drum, John Teufel and his colleagues were able to lower it to a temperature of about 360 microkelvin, or 10,000 times colder than the vacuum of space. “It’s much colder than any naturally occurring temperature anywhere in the universe,” says Teufel.
Supercooled systems like this tiny drum could be used as extremely sensitive and precise sensors for measuring force or acceleration, since they would register little random noise from their environment.
“In the near term, it’s about achieving the highest sensitivities that nature allows,” says Teufel. But further into the future, this sort of cooling may help us revolutionise quantum computing and probe the nature of the quantum world.
“Getting things cold is just another way of saying that you can engineer their state to be something that you want,” says Safavi-Naeini. Improving our ability to control the state of a system like this drum increases the possibility of being able to change it so we can measure the quantum properties that are usually only applied to individual particles.
“Why don’t we see these kind of quantum behaviors in our daily life, but we see them on an atomic scale?” Teufel asks. “Where is the line in between?” He hopes that supercooled systems like his team’s tiny drum might eventually be able to show us.