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'Quantum fridge' gets close to absolute zero

But will it cool a beer?

NIST scientists have demonstrated a solid state refrigerator that sucks energy out of objects using a trick of quantum physics in which hot electrons tunnel through a one-way junction, carrying heat with them.

It's been a long project: NIST first demonstrated the use of NIS (normal metal / insulator / superconductor) junctions for cooling back in 2005. However, it's taken this long to scale the device up from the micron scale into the device shown below:

NIST's superconducting fridge

NIST's quantum refrigerator

In this image, the “quantum fridge” is on the green circuit board, and it cooled the copper block down to cryogenic temperatures. In the demonstration, they used 700 pW of cooling power to cool the 1.9 cm3 block from 290 mK (milli-Kelvin) to 256 mK. The researchers' next target is to achieve base temperatures of 100 mK.

The copper block, according to project leader Joel Ullom, is around a million times the mass of the refrigerating elements.

The 48 cooling elements are sandwiches of normal metal separated from a superconductor by an insulator. When a voltage is applied across the sandwich, the hottest electrons tunnel across the insulator into the superconductor. As they do make the journey, the electrons carry heat and vibrational energy with them.

So where's the quantum physics in that, you might ask. The trick is this: to select the properties of the materials so that the NIS junction is energy-selective: only electrons with the right quanta of energy are permitted to cross the insulator into the superconductor.

As the researchers note in the abstract to their paper in Applied Physics Letters, “previous devices using this cooling principle fell short of general-purpose refrigerators since they could not be coupled to arbitrary payloads.”

And to answer the question in the sub-head, yes, the device probably could cool your beer. It might cheaper and more convenient, however, to buy yourself a beer fridge. ®

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