Quantum physicists succeed in controlling energy losses and displacements

Quantum computers must retain quantum information for a long time to be able to solve important problems faster than a normal computer. Energy losses take the state of the qubit from one to zero, destroying the quantum information stored at the same time. As a result, scientists around the world have always worked to eliminate all sources of energy loss – or dissipation – from these machines.

Dr. Mikko Mottonen from Aalto University and his research team have taken a different approach. "Years ago, we realized that quantum computers really need dissipation to work effectively, and the trick is to have them only when you need them," he says.

In their article to be published on March 11, 2019 in Physical Nature, scientists at Aalto University and the University of Oulu demonstrate that they can increase the dissipation rate by a factor of a thousand in a high-quality superconducting resonator on demand – such resonators are used in prototypes quantum computing.

"The quantum chip refrigerator we invented recently was the key to achieving this dissipative tunability.The future quantum computers need a similar feature to be able to control the loss of energy on demand" says Mottonen.

According to Dr. Matti Silveri, the first author of the book, the most significant results from a scientific point of view were unexpected.

"To our surprise, we found a change in the resonator frequency when we activated dissipation.7 Seventy years ago, Nobel laureate Willis Lamb first commented on the small variations in the resonator frequency. energy in the hydrogen atoms We observe the same first time in quantum technical systems, "says Silveri.

Lamb's observations were revolutionary at that time. They showed that modeling the atom of hydrogen was not enough; Electromagnetic fields must be taken into account, even if their energy is zero. This phenomenon is now also confirmed in quantum circuits.

The key to this new observation was that dissipation, and thus energy transfer, could be turned on or off. The control of these energy transfers is essential for the implementation of quantum logic and quantum computers.

"Building a quantum computer on a large scale is one of the biggest challenges in our society," said Mottonen.

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More information:
Moving lamb with broadband in an elaborate quantum system, Physical Nature (2019). DOI: 10.1038 / s41567-019-0449-0, https://www.nature.com/articles/s41567-019-0449-0