MIT researchers are developing a superconducting nanowire, which could enable more efficient superconducting electronics.
Superconductors — materials that conduct electricity without resistance — are remarkable. They provide a macroscopic glimpse into quantum phenomena, which are usually observable only at the atomic level. Beyond their physical peculiarity, superconductors are also useful. They’re found in medical imaging, quantum computers, and cameras used with telescopes.
But superconducting devices can be finicky. Often, they’re expensive to manufacture and prone to err from environmental noise. That could change, thanks to research from MIT.
The researchers are developing a superconducting nanowire, which could enable more efficient superconducting electronics. The nanowire’s potential benefits derive from its simplicity.
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.
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.
However, the Josephson junction is fundamentally quite a delicate object. That translates directly into cost and complexity of manufacturing. Josephson junction-based superconductors also may not play well with others.
To overcome these disadvantages, the MIT team is developing a new technology — the superconducting nanowire — with roots older than the Josephson junction itself.
In 1956, MIT electrical engineer Dudley Buck published a description of a superconducting computer switch called the cryotron. The device 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.
At the time, the cryotron was much smaller than other types of computing switches, like vacuum tubes or transistors, and Buck thought the cryotron could become the building block of computers. But in 1959, Buck died suddenly at age 32, halting the development of the cryotron. Since then, transistors have been scaled to microscopic sizes and today make up the core logic components of computers.
Now, MIT team is rekindling Buck’s ideas about superconducting computer switches. The devices they are making are very much like cryotrons in that they don’t require Josephson junctions, and they dubbed their superconducting nanowire device the nano-cryotron in tribute to Buck — though it works a bit differently than the original cryotron.
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 research team has already demonstrated proof-of-concept for the nano-cryotron’s use as an electronic component. A sample device is developed to add binary digits using nano-cryotrons . And the team has successfully used nano-cryotrons as an interface between superconducting devices and classical, transistor-based electronics.
The researchers say that this 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.
The nano-cryotron could one day find a home in superconducting quantum computers and supercooled electronics for telescopes. Wires have low power dissipation, so they may also be handy for energy-hungry applications.
News source: MIT
