Superconductors — materials that conduct electricity without resistance — provide a macroscopic glimpse into quantum phenomena, which are usually observable only at the atomic level. Superconductors are found in medical imaging, quantum computers, and cameras used with telescopes. But often, they are expensive to manufacture and prone to error from environmental noise.
Researchers are developing a superconducting nanowire that could enable more efficient superconducting electronics. Most metals lose resistance and become superconducting at extremely low temperatures — usually just a few degrees above absolute zero. They are used to sense magnetic fields, especially in highly sensitive situations like monitoring brain activity. They also have applications in both quantum and classical computing.
Underlying many of these superconductors is a device invented in the 1960s called the Josephson junction, which is essentially two superconductors separated by a thin insulator — it is what led to conventional superconducting electronics and then ultimately to the superconducting quantum computer.
The Josephson junction is costly and complex to manufacture, especially for the thin insulating later. Josephson junction-based superconductors also may not interface with conventional electronics like those in cellphones or computers — the noise from those swamps the Josephson junction.
In 1956, a superconducting computer switch called the cryotron was developed. It was little more than two superconducting wires: One was straight and the other was coiled around it. The cryotron acts as a switch, because when current flows through the coiled wire, its magnetic field reduces the current flowing through the straight wire.
The new device is very much like a cryotron in that it doesn’t require Josephson junctions. The superconducting nanowire device — called the nano-cryotron — uses heat to trigger a switch rather than a magnetic field. 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.
The superconducting nanowire could one day complement, or perhaps compete with, Josephson junction-based superconducting devices and find a home in superconducting quantum computers and supercooled electronics for telescopes.