In his quest to create a “topological insulator,” Rice graduate student Ivan Knez spent hundreds of hours modifying tiny pieces of semiconductors in Rice University’s clean room. Photo: Jeff Fitlow/Rice University |
Rice University physicists have created a tiny
“electron superhighway” that could one day be useful for building a
quantum computer, a new type of computer that will use quantum particles in
place of the digital transistors found in today’s microchips.
In a paper in Physical
Review Letters, Rice physicists Rui-Rui Du and Ivan Knez describe a new
method for making a tiny device called a “quantum spin Hall topological
insulator.” The device, which acts as an electron superhighway, is one of
the building blocks needed to create quantum particles that store and
manipulate data.
Today’s computers use binary bits of data that are either
ones or zeros. Quantum 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 gives quantum computers a huge edge in performing
particular types of calculations, says Du, professor of physics and astronomy
at Rice. For example, intense computing tasks like code-breaking, climate
modeling and biomedical simulation could be completed thousands of times faster
with quantum computers.
“In principle, we don’t need many qubits to create a
powerful computer,” he says. “In terms of information density, a
silicon microprocessor with 1 billion transistors would be roughly equal to a
quantum processor with 30 qubits.”
In the race to build quantum computers, researchers are
taking a number of 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. This is known as “fault
tolerance.”
The approach Du and Knez are following is called
“topological quantum computing.” Topological designs are expected to
be more fault-tolerant than other types of quantum computers because each qubit
in a topological quantum computer will be made from a pair of quantum particles
that have a virtually immutable shared identity. The catch to the topological
approach is that physicists have yet to create or observe one of these stable
pairs of particles, which are called Majorana fermions.
The elusive Majorana fermions were first proposed in 1937,
although the race to create them in a chip has just begun. In particular,
physicists believe the particles can be made by marrying a 2D topological
insulator—like the one created by Du and Knez—to a superconductor.
Topological insulators are oddities; although electricity
cannot flow through them, it can flow around their narrow outer edges. If a
small square of a topological insulator is attached to a superconductor, Knez
says, the elusive Majorana fermions are expected to appear precisely where the
materials meet. If this proves true, the devices could potentially be used to
generate qubits for quantum computing, he says.
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 making night-vision goggles. Du says it
is the first 2D topological insulator made from a material that physicists
already know how to attach to a superconductor.
“We are well-positioned for the next step,” Du
says. “Meanwhile, only experiments can tell whether we can find Majorana
fermions and whether they are good candidates for creating stable qubits.”