Researchers Move a Step Closer to Quantum Computers

on October 06 2011 2:26 AM

Physicists at Rice University in Houston, Texas have created a tiny electron superhighway that could one day be useful for building a quantum computer, which will use qubits or quantum bits to encode information, the university says.

Rui-Rui Du, a professor of physics and astronomy, and his colleague Ivan Knez have created a small device called a quantum spin Hall topological insulator. This device could be an essential building block in the creation of quantum particles that can, in turn, store and manipulate data.

Unlike silicon-based computers that use binary codes (ones and zeroes) to work through calculations, quantum computers are based on what are called superpositions -- the idea that matter can exist, simultaneously, in multiple positions. In essence, qubits can be both ones and zeros at the same time.

This quirk gives quantum computers a huge edge in performing particular types of calculations. For example, intense computing tasks like code-breaking, climate modeling and biomedical simulation could be completed thousands of times faster with quantum computers, said Du.

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

In the race to build quantum computers, physicists are using various approaches to create these qubits. The point where all of them, until now at least, were coming undone is that information encoded into qubits is subject to quantum fluctuations. Over time, qubits lose data encoded into them. Du and Knez worked on a model 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. However, physicists have yet to create or observe such a pair, called Majorana fermions. These were first proposed in 1937.

Researchers today are of the opinion that these particles can be made by combining a two-dimensional topological insulator -- like the one created by Du and Knez -- to a superconductor.

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, the devices could potentially be used to generate qubits for quantum computing, said Knez, who spent more than a year refining the techniques.

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, said Du.

The results of Du's and Knez's research were recently published in Physical Review Letters.