Meet the Quantum Fridge
Centre for Quantum Technologies researchers have built a refrigerator that's just three atoms big.
This quantum fridge won't keep your drinks cold, but it’s cool proof of physics operating at the smallest scales.
Researchers have built tiny 'heat engines' before, but quantum fridges existed only as proposals until now.
The device is an ‘absorption refrigerator’. It works without moving parts, using heat to drive a cooling process. The first absorption refrigerators, introduced in the 1850s, were used to make ice and chill food into the 20th century.
The fridge was created in the experimental lab of Prof Dzmitry MATSUKEVICH using exquisite control over individual atoms.
First, the researchers caught and held three atoms of the element Ytterbium in a metal chamber from which they had removed all the air. They also pulled one electron off each atom to leave them with a positive charge. The charged atoms were held in place with electric fields.
The researchers nudged and zapped the ions with lasers to bring them into their lowest energy state of motion. The lasers also injected heat, making the ions wiggle about. The energy of the wiggling ions is quantised in ‘phonons’. By tuning the wiggling frequencies, the researchers set up conditions for refrigeration - making it such that a phonon moving from the see-saw to the slinky mode would drag a phonon from the zig-zag mode with it. The zig-zag mode thus loses energy, and its temperature drops.
Studying such small devices shows the role of quantum effects in thermodynamics.
Prof Valerio SCARANI, a member of the team, said, “"The next question is, can you cool what you want with it? So far, we have the engine of the fridge, but not the box for the beer."
Reference: Gleb MASLENNIKOV, Shiqian DING, Roland HABLÜTZEL, Jaren GAN, Alexandre ROULET, Stefan NIMMRICHTER, Jibo DAI, Valerio SCARANI and Dzmitry MATSUKEVICH, “Quantum absorption refrigerator with trapped ions”, Nature Communications 10, 202 (2019)
Adapted from the Centre for Quantum Technologies’ public release