The Cryotron: Superconducting Nano-Wire May be Enroute to Your Quantum Computer

Nanowire could provide a stable superconducting transistor

+  Most metals lose resistance and become superconducting at extremely low temperatures, usually just a few degrees above absolute zero. They’re used to sense magnetic fields, especially in highly sensitive situations like monitoring brain activity. They also have applications in both quantum and classical computing.

Berggren said his group’s superconducting nanowire could one day complement – or perhaps compete with – Josephson junction-based superconducting devices. “Wires are relatively easy to make, so it may have some advantages in terms of manufacturability,” he said.

+  Underlying many of these superconductors is a device invented in the 1960s called the Josephson junction – essentially two superconductors separated by a thin insulator. “That’s what led to conventional superconducting electronics, and then ultimately to the superconducting quantum computer,” Berggren said.

+  However, the Josephson junction “is fundamentally quite a delicate object,” Berggren added. That translates directly into cost and complexity of manufacturing, especially for the thin insulating later. Josephson junction-based superconductors also may not play well with others: “If you try to interface it with conventional electronics, like the kinds in our phones or computers, the noise from those just swamps the Josephson junction. So, this lack of ability to control larger-scale objects is a real disadvantage when you’re trying to interact with the outside world.”

+ To overcome these disadvantages, Berggren is developing a new technology – the superconducting nanowire – with roots older than the Josephson junction itself.

+  The nano-cryotron uses heat to trigger a switch, rather than a magnetic field. In Berggren’s device, current runs through a superconducting, supercooled wire called the “channel.” That channel is intersected by an even smaller wire called a “choke” – like a multilane highway intersected by a side road. When current is sent through the choke, its superconductivity breaks down and it heats up. Once that heat spreads from the choke to the main channel, it causes the main channel to also lose its superconducting state.

Source:  Control Engineering.  Daniel Ackerman,  Nanowire could provide a stable superconducting transistor…

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