Researchers at the National Institute of Standards and Technology (NIST) in the United States have demonstrated a solid-state refrigerator that uses quantum physics in micro- and nanostructures to cool a much larger object to extremely low temperatures – and here we’re talking sub-cryogenic.
What’s more, the prototype NIST refrigerator, which has very modest outer dimensions, enables researchers to place any suitable object in the cooling zone and later remove and replace it, similar to an all-purpose kitchen refrigerator. The cooling power is the equivalent of a window-mounted air conditioner cooling a building the size of the Lincoln Memorial in Washington, DC.
“It’s one of the most flabbergasting results I’ve seen,” says project leader Joel Ullom. “We used quantum mechanics in a nanostructure to cool a block of copper. The copper is about a million times heavier than the refrigerating elements. This is a rare example of a nano- or microelectromechanical machine that can manipulate the macroscopic world.”
The technology may offer a compact, convenient means of chilling advanced sensors below standard cryogenic temperatures – 300 milliKelvin (mK), typically achieved by use of liquid helium – to enhance their performance in quantum information systems, telescope cameras, and searches for mysterious dark matter and dark energy.
As described in Applied Physics Letters, the NIST refrigerator’s cooling elements, consisting of 48 tiny sandwiches of specific materials, chilled a plate of copper, 2,5 cm on a side and 3 mm thick, from 290 mK to 256 mK. The cooling process took about 18 hours. NIST researchers expect that minor improvements will enable faster and further cooling to about 100 mK.
The cooling elements are sandwiches of a normal metal, a 1 nanometre-thick insulating layer, and a superconducting metal. When a voltage is applied, the hottest electrons “tunnel” from the normal metal through the insulator to the superconductor. The temperature in the normal metal drops dramatically and drains electronic and vibrational energy from the object being cooled.
NIST researchers previously demonstrated this basic cooling method but are now able to cool larger objects that can be easily attached and removed. Cooling to temperatures below 300 mK currently requires complex, large and costly apparatus. NIST researchers, whose work is supported by Nasa, plan to boost the cooling power of the prototype refrigerator by adding more and higher-efficiency superconducting junctions and building a more rigid support structure.