New technology could boost quantum computers

Nanowire could provide a stable, easy-to-make superconducting transistor.


Beyond their actual property, superconductors are remarkable and likewise valuable. They’re found in clinical imaging, quantum PCs, and cameras utilized with telescopes.

However, superconducting gadgets can be finicky. Frequently, they’re costly to produce and inclined to err from environmental noise. 

A recent study could change that. Scientists from Karl Berggren’s group in the Department of Electrical Engineering and Computer Science are developing a superconducting nanowire, enabling more efficient superconducting electronics. The nanowire’s potential benefits derive from its simplicity.

In 1956, MIT electrical Dudley Buck published a depiction of a superconducting computer switch called the cryotron, a device that was little more than two superconducting wires: One was straight, and the other was curled around it. The cryotron goes about as a switch since when the current courses through the coiled wire, its magnetic field reduces the current moving 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. Since then, transistors have been scaled to microscopic sizes and today make up the core logic components of computers.

Now, Berggren is rekindling Buck’s ideas about superconducting computer switches.

Berggren said, “The devices we’re making are very much like cryotrons in that they don’t require Josephson junctions. Our 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, as opposed to a magnetic field. In Berggren’s device, current runs through a superconducting, supercooled wire called the “channel.” An even smaller wire intersects that channel called a “choke”. 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 also causes the main channel to lose its superconducting state.

Scientists have already shown proof-of-concept for the nano-cryotron’s use as an electronic component. A previous understudy of Berggren’s, Adam McCaughan, built up a gadget that utilizes nano-cryotrons to add binary digits. Also, Berggren has effectively used nano-cryotrons as an interface between superconducting devices and classical, transistor-based electronics.

Berggren said“Our superconducting nanowire could one day complement — or perhaps compete with — Josephson junction-based superconducting devices. “Wires are relatively easy to make so that 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.”

“It’s probably not going to replace the transistors in your phone, but if it could replace the transistor in a server farm or data center? That would be a huge impact.”

“We’re doing fundamental research here. While we’re interested in applications, we’re just also interested in: What are some different kinds of ways to do computing? As a society, we’ve focused on semiconductors and transistors. But we want to know what else might be out there.”

Berggren will present a summary of the research at this month’s IEEE Solid-state Circuits Conference.

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