Electron superhighway paves way for quantum computer

Rice University physicists have created a tiny “electron superhighway” that could help scientists design a quantum-based computer at some point in the future.

The device – which is described as a “quantum spin Hall topological insulator” – is one of the essential building blocks needed to create quantum particles capable of storing and manipulating data.

According to Rice physicist Rui-Rui Du, today’s computers use binary bits of data that are either ones or zeros. However, quantum-powered computers would use quantum bits, or “qubits,” which can be both ones and zeros at the same time, thanks to the quirks of quantum mechanics.

This quirk would provide quantum computers with a huge edge in performing particular types of calculations, including code-breaking, climate modeling and biomedical simulation.

“In principle, we don’t need many qubits to create a powerful computer,” explained Du. “In terms of information density, a silicon microprocessor with 1 billion transistors would be roughly equal to a quantum processor with 30 qubits.”

Perhaps not unsurprisingly, researchers have adopted various approaches to creating qubits. Regardless of the approach, a common problem is making certain that information encoded into qubits isn’t lost over time due to quantum fluctuations.

The approach followed by Du and colleague Ivan Knez is known as “topological quantum computing,” which is expected to be more fault-tolerant than other types of quantum computers. This is because each qubit in a topological quantum computer will be made from a pair of quantum particles that have a virtually immutable shared identity. 

Unfortunately, the catch to the topological method is that physicists have yet to create or observe one of these stable pairs of particles, which are known as “majorana fermions.” 

The relatively elusive Majorana fermions were first proposed in 1937, although the race to create them in a chip has just begun.

Physicists now believe the particles can be made by “marrying” a two-dimensional topological insulator – like the one created by Du and Knez – to a superconductor. Yet, topological insulators are often thought of as peculiar oddities. Although electricity cannot flow through them, it is capable of flowing around their narrow outer edges. 

As such, if a small square of a topological insulator is attached to a superconductor, the elusive Majorana fermions are expected to appear precisely where the materials meet. If this proves true, says Knez, the devices could potentially be used to generate qubits for quantum computing.

Knez spent more than a year refining the techniques to create Rice’s topological insulator. The device is made from a commercial-grade semiconductor that’s commonly used in designing night-vision goggles. 

“We are well-positioned for the next step… Meanwhile, only experiments can tell whether we can find Majorana fermions and whether they are good candidates for creating stable qubits,” added Du.