Scientists and engineers from the Universities of Bristol and Western Australia have developed how to efficiently simulate a ‘quantum walk’ on a new design for a primitive quantum computer.

Quantum computers have the potential to open entirely new directions for processing information and to overhaul the way that we think about and use the science of computation. There are some problems that traditional computers cannot solve in a useful amount of time, no matter how fast they become. Quantum computing aims to address this, exploring uncharted computation and solving at least some of these problems that classical computers cannot.

The researchers have produced evidence that with this method something meaningful can already be seen with a primitive quantum computer that cannot be seen with a classical computer. The first steps towards this have been implemented in the lab in Bristol.

Dr Ashley Montanaro, lecturer in the University of Bristol's School of Mathematics, said: "We know some algorithms that can run on such machines and it's an open and exciting challenge to find more. But most of the quantum algorithms we know need to be run on a large-scale quantum computer to see a speed up."

Building a large-scale quantum computer is one of the biggest engineering challenges today. There's a growing worldwide effort to develop one and it needs substantial effort from a range of expertise. The results could offer fast and cheap ways to design new materials and new pharmaceuticals.

But there is a field of research emerging that can help accelerate understanding how quantum computers will work and how users can apply them. Examining the power of smaller, more primitive designs for quantum computers indicates that soon, quantum machines could outperform the capabilities of classical computing for very specific tasks – ‘Boson Sampling’ is a recent example that is driven by what could soon be experimentally available.

Questions researchers face include what can these primitive quantum processors do that is useful to someone and how sophisticated do they need to be. The results of the research help to answer this question, by looking at how to simulate particular kinds of a phenomenon called the quantum walk.

The quantum walk is the quantum mechanical version of models such as Brownian motion and the ‘drunken sailor's random walk’. The key difference is the particle in the quantum walk is endowed with the principle of quantum superposition. This has enabled researchers to show they are a new way to think about how full-scale quantum computers might operate and to create useful quantum algorithms.

Xiaogang Qiang, PhD student in the University of Bristol’s School of Physics who implemented the experiment, said: "It's like the particle can explore space in parallel. This parallelism is key to quantum algorithms, based on quantum walks that search huge databases more efficiently than we can currently."

Dr Jonathan Matthews, lecturer in the School of Physics and the Centre for Quantum Photonics, explained: "An exciting outcome of our work is that we may have found a new example of quantum walk physics that we can observe with a primitive quantum computer, that otherwise a classical computer could not see.

"These otherwise hidden properties have practical use, perhaps in helping to design more sophisticated quantum computers."