Cooling has proven to be a major concern for engineers developing quantum computers, but now a research team at Finland’s Aalto University says it has invented a quantum circuit refrigerator that could reduce errors in quantum computing. Quantum computers differ from the computers that we use in that, instead of computing using normal bits, they use quantum bits, or qubits. The bits being crunched in your laptop are either zeros or ones, whereas a qubit can exist simultaneously in both states. To obtain correct computational results, every qubit has to be reset at the beginning of a computation. If the qubits are too hot, they cannot be initialized because they are switching between different states too much.
The nanoscale refrigerator developed by the Aalto team will allow most electrical quantum devices to be initialized quickly, making the machines more powerful and reliable. “I have worked on this gadget for five years and it finally works,” says Kuan Yen Tan, a postdoctoral researcher in the group.
Tan cooled down a qubit-like superconducting resonator utilizing the tunneling of single electrons through a two-nanometer-thick insulator. He gave the electrons slightly too little energy from an external voltage source than what is needed for direct tunnelling. Therefore, the electron captures the missing energy required for tunneling from the nearby quantum device, and hence the device loses energy and cools down. The cooling can be switched off by adjusting the external voltage to zero. Then, even the energy available from the quantum device is not enough to push the electron through the insulator.
Next, the group plans to cool actual quantum bits in addition to resonators. The researchers also want to lower the minimum temperature achievable with the refrigerator and make its on/off switch super fast.