The promise of quantum computing is largely predicated on whether or not physicists can keep quantum bits, or "qubits," from slipping out of their two-state existence due to quantum fluctuations. This fundamental limitation has spawned research into different approaches to creating qubits.
Credit: Jeff Fitlow/Rice University
The latest comes from Rice University, where physicists have created a device called a "quantum spin Hall topological insulator" which acts as a tiny electron superhighway designed for increased fault-tolerance.
The researchers claim that the device is one of the building blocks needed to create quantum particles that store and manipulate data.
A quantum computer uses quantum particles in place of the digital transistors found in today's microchips. These particles -- atoms, electrons, or qubits -- can be both ones and zeros at the same time, thanks to the quirks of quantum mechanics. This gives quantum computers a huge edge in performing intense computing tasks like code-breaking, climate modeling and biomedical simulation.
"In principle, we don't need many qubits to create a powerful computer. In terms of information density, a silicon microprocessor with 1 billion transistors would be roughly equal to a quantum processor with 30 qubits," said Rui-Rui Du, a Rice physicist behind the research.
According to Rice, "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."
But there is a catch to the topological approach. Physicists have yet to create or observe one of these stable pairs of particles, which are called "Majorana fermions" (pronounced MAH-yor-ah-na FUR-mee-ons).
Majorana fermions were first proposed in 1937 and the search for the elusive particles is becoming an obsession in the condensed-matter community. Physicists believe the particles can be made by marrying a two-dimensional topological insulator -- like the one created by Du and Knez -- to a superconductor.
According to Knez, if a small square of a topological insulator is attached to a superconductor then 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.
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 said it is the first 2-D 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 said. "Meanwhile, only experiments can tell whether we can find Majorana fermions and whether they are good candidates for creating stable qubits."