The next step in quantum computing

A team of physicists in the United States has made an important step towards making quantum computing a reality. Research into a new type of noiseless quantum information bit, or qubit, is published today in the joint Institute of Physics and German Physical Society journal, New Journal of Physics.

At a sub-atomic scale the laws of quantum physics lead to strange new properties of matter. For several years physicists have been trying to exploit this quantum weirdness to build a new type of `quantum computer`. Such a computer would be able to solve problems like searching databases and cracking currently unbreakable encryption codes in many fewer steps than any computer existing today.

But the goal of building a quantum computer has been frustrated by the effects of noise. In a quantum computer, the basic unit of information – the qubit – is as small as a single atomic nucleus. Its size makes it sensitive to many small external sources of noise, and these rapidly destroy the information. Now Evan Fortunato of the Massachusetts Institute of Technology and colleagues, in collaboration with Los Alamos National Laboratory researcher Lorenza Viola, have shown how to protect and control a bit of quantum information in the presence of noise.

The information is encoded within two atomic nuclei inside a molecule. The central idea behind the technique is that certain types of noise leave part of the system naturally protected. Even when the molecule is subject to external noise, the quantum information it contains is not destroyed. Although previous work by both this and other research groups was successful at storing quantum information in one-bit `quantum memories`, no previous results have demonstrated the manipulation of the quantum information in the presence of noise.

The team has demonstrated the effect using liquid-state nuclear magnetic resonance techniques. The experiments have shown that the information can be processed through the application of logic gates while remaining, to a large extent, protected against strong noise sources. This noise-tolerant manipulation of quantum information may be a key step in the route toward working quantum computers.

“We believe learning how to make protected quantum bits that can be effectively manipulated will prove a key step in developing and benchmarking quantum information processing devices”, said Dr Viola. “Our results represent a first experimental step in that direction, and will hopefully motivate other researchers to explore similar strategies for different device technologies”, she added.