Computers Making the Quantum Leap

One branch of physics holds huge implications for information technologies.

Quantum computational devices with calculating power greater than any of today’s conventional computers could be just a decade away, says Bristol University physicist and electrical engineer Mark Thompson. He anticipates accelerated research and development breakthroughs in many fields of science, thanks to quantum computing.

At a January 2011 Cambridge University forum, Thompson presented two Bristol-developed quantum photonic computer chips, which process photons (particles of light). One chip used a quantum algorithm to find the prime factors of 15. Thompson says that factoring numbers is hard for conventional computers but would be relatively easy for quantum computers.

With further development, quantum processing could create powerful simulation tools for modeling many natural processes, such as superconductivity and photosynthesis. Quantum computers might also model molecular and subatomic systems with greater precision than today’s computers can.

“We plan to perform calculations that are exponentially more complex, and will pave the way to quantum computers that will help us understand the most complex scientific problems,” says Thompson.

A conventional computer stores information in bits, each bit either a 0 or 1. A quantum computer would store information in “qubits,” and each qubit could be both 1 and 0 at the same time. David Lee Hayes, a researcher at the University of Maryland’s Joint Quantum Institute, explains that a particle in a quantum state is in “superposition”: It can be in more than one place at the same time. It assumes one location, however, once someone observes it.

“You can think of the observer as getting entangled with the quantum bit in a weird way,” says Hayes.

Entanglement, another property of quantum particles, means that one quantum particle links telepathically to another particle far away. The second particle then exactly imitates all its partner’s properties.

Since qubits can hold more than one location at once, a quantum computer could compute many more problems at once, according to Carl Williams, chief of the Atomic Physics Division at the U.S. National Institute of Standards and Technology.

Such a computer would be a powerful tool for pharmaceutical developers, says Williams. Drug researchers now use conventional computers to model the human body’s chemical systems and project how certain chemical compounds might interact with it. The models guide the researchers’ synthesis of experimental new drugs.

The modeling processes involve millions of calculations. A quantum computer might complete the same calculations much more quickly and speed up drug development.

“Our time scale for developing new drugs would become cheaper and faster,” says Williams. “Researchers would only have to synthesize those things that are going to work.”

The quest to build a quantum computer is becoming a race, according to Martin Rotteler, head of the quantum computing research group at NEC Laboratories. He says that NEC has built a quantum computing device that has two qubits of memory, but other labs have built devices with three qubits of memory, and someone may build a four- or five-qubit device in another three to five years.

Rotteler says that quantum computers would be optimum for working on problems in which there is a lot of structure, such as a graph. They could also map magnetic fields, protein folding, and other natural systems down to magnitudes of detail that are impossible today.

Building a quantum computer will require more efficient ways of controlling quantum phenomena, according to Williams. Quantum particles can easily entangle with particles they are not supposed to entangle with, or interact with each other in ways that the researchers do not intend.

Also, creating qubits and photons requires massive system components. But just as the first conventional computers filled entire rooms and were later replaced by progressively more-compact successors, quantum computing could evolve into smaller and cheaper systems.

“Build the first one,” says Williams, “and in 25 years, they will be 25% of the size. I bet that, after the first quantum computer, the cost of one 10 years later will be significantly reduced.”—Rick Docksai

Sources: David Lee Hayes, University of Maryland Joint Quantum Institute, http://jqi.umd.edu.

Martin Rotteler, NEC Labs, www.nec-labs.com.

Mark Thompson, Bristol University, www.bris.ac.uk.

Carl Williams, NIST, www.nist.gov.