Quantum fridge hits record low

SWEDEN/USA: Researchers claim to have have engineered a new type of refrigerator that can cool superconducting qubits to record low temperatures.

Quantum computers require extreme cooling to perform reliable calculations. One of the challenges preventing quantum computers from entering society is the difficulty of freezing quantum bits or “qubits” to temperatures close to absolute zero.

Now, researchers at Chalmers University of Technology, Sweden, and the University of Maryland, USA, have engineered a refrigerator that can autonomously cool superconducting qubits to record low temperatures, paving the way for more reliable quantum computation.

For qubits to work without errors and for longer periods in such a system, they need to be cooled to a temperature close to absolute zero, equivalent to -273.15ºC or zero Kelvin.

The cooling systems used today, so-called dilution refrigerators, bring the qubits to about 50mK above absolute zero. The closer a system approaches to absolute zero, the more difficult further cooling is. 

While, according to the laws of thermodynamics, no finite process can cool any system to absolute zero, the Swedish and US researchers have constructed a new type of quantum refrigerator based on superconducting circuits that can complement the dilution refrigerator. Powered by heat from the environment, it can cool the target qubit to 22mK, without external control.

The refrigerator utilises interactions between different qubits, specifically between the target qubit to be cooled and two quantum bits used for cooling. Next to one of the qubits, a warm environment is engineered to serve as a hot thermal bath. The hot thermal bath gives energy to one of the quantum refrigerator’s superconducting qubits and powers the quantum refrigerator.

The quantum refrigerator is described in an article in the journal Nature Physics.