Dirty Or Clean, Graphene Could Make A Nice Little Quantum Computer

December 23rd, 2013 by Tina Casey

An international team of researchers based at MIT has figured out how to make the edges of the two-dimensional wonder material graphene behave like one-dimensional electronic wires. I know, right? To ice the cake, the edges don’t have to be perfectly formed. They can be irregular or “dirty” and those electrons would still go zipping along in the right direction.

In terms of quantum computers, that’s an important advantage for graphene. Graphene, which we’ve dubbed the nanomaterial of the new millennium, is a single layer of carbon atoms that you can lift from a chunk of graphite with sticky tape (that’s what the original researchers did when they discovered it back in 2004).

Graphene is cheap compared to other materials with quantum computer potential but it is notoriously difficult to fabricate perfect examples in bulk, so if a measure of imperfection does not interfere with its efficiency, finding applications for it would be that much more likely.

Graphene And Quantum Computing

Despite its famously slim silhouette, graphene has been estimated to have 200 times the strength of steel while possessing unique electronic properties that have intrigued thousands of researchers since its discovery in 2004.

In terms of the usefulness of graphene in next-generation computers, think back to the difference between your smart phone and the bulky mainframe/punched card system of just a few generations ago. Now think ahead to what that will come after your phone, and you’re talking about a computer that operates on an atomic scale, otherwise known as a quantum computer.

One key to quantum computing, according to our friends over at Lawrence Berkeley National Laboratory, is to develop a “fault-tolerant” material from an exotic class of materials called topological conductors, which have an insulating interior but are conductors on the surface.

That fits the MIT graphene research to a T, except that in its normal state graphene is not a topological conductor.

As described by MIT writer David Chandler, in order to get graphene to behave like a topological conductor, the research team subjected a flake of graphene to a 35-tesla magnetic field (think of an MRI machine, times ten) under a temperature of just 0.3 degrees Celsius [update: that’s 0.3 degrees Celsius above absolute zero, not just plain old 0.3 degrees Celsius].

Here’s what happened when they turned the field perpendicular to the flake, keeping in mind that normally graphene is a conductor throughout its structure:

…the behavior changes: Current flows only along the edge, while the bulk remains insulating. Moreover, this current flows only in one direction — clockwise or counterclockwise, depending on the orientation of the magnetic field — in a phenomenon known as the quantum Hall effect.

By exposing the flake to another magnetic field in the same plane, the researchers got electrons to move around the edges in different directions. Combine that with switchability (the edge states can be turned on and off at will), there you have the makings of atom-scale circuits and transistors.

Next Steps To A Quantum Computer

I know what you’re thinking. You’re thinking that in the real world, a computer that needs a couple of 35-tesla magnetic fields and freezing temperatures to operate will never go in your pocket.









Well, according to Chandler, the research team is already working on a system that requires less extreme conditions.

We’re still years away from quantum computing, but in the mean time you’ll see graphene popping up in all kinds of other applications, including EV batteries, printable “electronic ink,” ultra-thin solar cells, and catalysts for converting carbon dioxide into fuel.

Image: Courtesy of MIT.

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