In quantum computers, the superpositions and entanglements of the qubits are fragile. Qubits must not only be accurately configured, but their quantum coherence needs to survive for the entire calculation. Isolation from the environmental perturbations is essential. Yet the isolation can extract a price on operating temperature and initialization times.
Kuan Yen Tan, Mikko Möttönen, and colleagues at Aalto University in Finland now report a proof-of-concept demonstration of a quantum-circuit refrigerator (QCR). They used as their prototype circuit a qubit-like superconducting microwave resonator. To cool the resonator, the team embedded a normal-metal segment connected via tunnel junctions to two superconducting leads. The photo shows a centimeter-sized silicon chip with a pair of serpentine resonators; the rectangles attached to each resonator are bonding pads, two for the micron-sized QCR and two for a thermometer to monitor the resonator temperature.
The QCR can be switched on and off on demand by adjusting...
