Researchers at the University of Singapore are reported to have built a refrigerator that’s just three atoms in size.
Researchers have built tiny “heat engines” before, but quantum fridges existed only as proposals until the team at the Centre for Quantum Technologies at the National University of Singapore chilled with their atoms.
“Our device is the first implementation of the absorption refrigeration cycle on the nanoscale,” claims Stefan Nimmrichter, co-author of a paper published in Nature Communications.
To create an absorption fridge with just three atoms, the researchers caught and held three atoms of ytterbium in a metal chamber from which they’d removed all the air. They also pulled one electron off each atom to leave them with a positive charge.
The charged ions can then be held in place with electric fields. Meanwhile, the researchers nudge and zap the ions with lasers to bring them into their lowest energy state of motion. The result is that the ions are suspended almost perfectly still, strung out in a line.
Another laser zap then injects some heat, making the ions move in three modes – an axial and two radial ones. By tuning the movement frequencies, the researchers set up conditions for refrigeration.
At its coldest, it is said to be within 40microK of absolute zero. Each round of preparing the ions and counting phonons took up to 70ms, with cooling happening for around 1ms. This process was said to have been repeated thousands of times.