Magnetic Josephson effect

A fundamental prediction of superconductivity theory has been demonstrated in the lab for the first time. An international team of physicists has observed coherent quantum phase slip, a phenomenon similar to the well-known Josephson effect in which magnetic flux takes the place of electric charge. Its discovery has fundamental implications for our understanding of macroscopic quantum systems and could also lead to intriguing applications, including a possible way to produce a qubit in a quantum computer.

Alexey Bezryadin, at the University of Illinois at Urbana-Champaign, believes that the work marks a significant achievement, both in terms of its progress in fundamental physics and its potential for application. “I would say there are two significant features to this work,” he says. “One is that the observation of these coherent quantum phase slips extends the applicability of quantum mechanics to more complex macroscopic systems. The applied aspect is that there are predictions that, if coherent quantum phase slips can exist (and this paper demonstrates that they do), you can use that to build certain useful devices.”

Astafiev agrees: “The phenomenon that we demonstrated is fundamental. As fundamental, I would imagine, as the Josephson effect. Josephson physics has proved very rich and there are many very useful devices based on the Josephson effect.” He believes it should be possible to exploit coherent quantum phase slip to build devices analogous to those based on the Josephson junction. In particular, Astafiev, who has a specific interest in quantum computing, hopes that qubits based on coherent quantum phase slip may not be prone to “charge noise” – a type of noise caused by the presence of an insulator that tends to cause quantum decoherence in Josephson qubits.

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