Future Quantum Computers Begin to Take Shape
A quantum computer chip that contains four "quantum bits" that can perform calculations.
CREDIT: Erick Lucero
VANCOUVER — Cracking the most secure codes in existence might require a computer farm covering much of North America to run at full speed for 10 years, even if it did not consume all of the Earth's energy in a single day. By contrast, a future quantum computer the size of a building might only take 16 hours and have about the same power requirements as today's supercomputers.
Science still remain decades away from making a quantum computer capable of harnessing the wildly strange behavior of particles on small scales — the "quantum mechanics" that allow particles to exist in two different states at once. But researchers have finally reached the point where they can begin to envision what a quantum computer might look like.
"We've taken a problem that I used to think was an insanely difficult problem and we've turned it into something that I now think is merely very, very hard," said John Martinis, a physicist at the University of California Santa Barbara.
Martinis described the vision for a possible quantum computer as one of several leading researchers in the field who spoke at the annual meeting of the American Association for the Advancement of Science in Vancouver on Feb. 18.
Quantum computers would not replace desktop or laptop PCs. Instead, they could help crack encoded communications by solving the complex math problems at the heart of their encryption, or better simulate the workings of quantum mechanics that seem to defy the usual rules of classical physics.
A better understanding of quantum mechanics also could lead to the development of new materials or the tailoring of molecules for specific tasks on tiny scales, said John Preskill, a physicist at the California Institute of Technology.
"We don't currently envision you'll be sending your email and processing on a quantum computer," Preskill said. "On the other hand, quantum games might be a blast. It could affect lives in ways we haven't anticipated."
First, scientists must figure out how to build stable quantum computers by trapping electrons or other quantum particles to represent digital bits of information in their different states. Such particles can store more information than normal by existing in several states at once through "quantum superposition."
The particles can also take advantage of what Albert Einstein called "spooky action at a distance" — the quantum entanglement phenomenon that can keep two particles connected even when separated by an entire galaxy.
But such particles must also remain isolated so that outside forces don't affect their state of existence. Any changes to their state can lead to "quantum discoherence" and computing errors that require constant error-checking and correction.
Some labs have pushed ahead with trapping two or four quantum particles as the starting foundation for building quantum computers. Others have backed the more theoretical idea of a "topological quantum computer" — based on materials such as gallium arsenide — that have more structural stability to avoid the errors caused by outside influences.
"We don't know for sure what the hardware is going to look like, but a number of different approaches are being developed," Preskill said.