Quantum computers make light work of chemistry
Monday, January 11, 2010
Physicists have a problem.
They have an outstandingly successful theory of nature at the small scale—quantum mechanics—but have been unable to apply it exactly to situations more complicated than, say, 4 or 5 atoms—let alone a caffeine or cholesterol molecule.
Instead, they have developed a host of approximate methods to use quantum mechanics in fields such as biology, chemistry, and materials science, but this approach raises the concern that natural behaviours are being missed, and limits the development of new technologies.
Nearly thirty years ago Nobel Prize winning physicist Richard Feynman proposed a better solution: to use computers that are themselves quantum mechanical, a hypothetical device now known as a quantum computer.
This week an international team of scientists based in Australia and the US have done exactly that: building a small quantum computer and used it to calculate the precise energy of molecular hydrogen.
This groundbreaking approach to molecular simulations could have profound implications not just for chemistry, but also for a range of fields from cryptography to materials science.
The work, described this week in Nature Chemistry, comes from a partnership between a group of physicists—led by Professor Andrew White at the University of Queensland in Brisbane, Australia—and a group of chemists—led by Professor Alán Aspuru-Guzik at Harvard University, Cambridge, USA.
White's team assembled the physical computer and ran the experiments and Aspuru-Guzik's team coordinated experimental design and performed key calculations. "We were the software guys", says Aspuru-Guzik, "and they were the hardware guys".
"Our results agreed with those calculated using a traditional computer to within six parts to a million", says White, "which we were pretty happy with".
While modern supercomputers can perform approximate simulations, increasing the complexity of these systems results in exponential increase in computational time. Quantum computers promise highly precise calculations while using a fraction the resources of conventional computing.
This computational power derives from the way quantum computers manipulate information. In classical computers, information is encoded in bits, that have only two values: zero and one; quantum computers use quantum bits?qubits?that can have an infinite different number of values: zero, or one, or zero plus one, and so on.
Quantum computers also exploit the strange phenomena of entanglement, powerful correlations between qubits that Einstein once described as "spooky action at a distance".
When asked when quantum computers will leave the lab and appear on desktops, White smiles ?Later than I?d like but sooner than I think?, he replies.
"It's very early days for quantum technology", he continues, "most quantum computer demonstrations have been limited to a handful of qubits. A colleague of mine in Canada says that any demonstration with less than ten qubits is cute but useless—which makes me think of a baby with an abacus."
"However Alan and his team at Harvard have shown that when we can build circuits of just a few hundred qubits, this will surpass the combined computing power of all the traditional computers in the world, each of which uses many billions of bits."
"It took standard computing 50 years to get to this point, I?m sure we can do it in much less time than that!"
White's University of Queensland co-authors on the Nature Chemistry paper are Benjamin P. Lanyon, Geoffrey G. Gillet, Michael E. Goggin, Marcelo P. Almeida, Benjamin J. Powell, and Marco Barbieri. Financial support was provided by the Australian Research Council Federation Fellow and Centre of Excellence programs, and the US Army Research Office (ARO) and Intelligence Advanced Research Projects Initiative (IARPA).
For more information contact Professor Andrew White by phone, office: +61 7 3365 7902 or by email: agx.white@gmail.com. Background information at http:// quantum.info/news .
Offical press releases from the University of Queensland and Harvard University.