It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
For 30 years, researchers have pursued the universal quantum computer, a device that could solve any computational problem, with varying degrees of success. Now, a team in California and Spain has made an experimental prototype of such a device that can solve a wide range of problems in fields such as chemistry and physics, and has the potential to be scaled up to larger systems.
Both IBM and a Canadian company called D-Wave have created functioning quantum computers using different approaches. But their devices are not easily scalable to the many quantum bits (qubits) needed for solving problems that classical computers cannot.
Computer scientists at Google’s research laboratories in Santa Barbara, California, and physicists at the University of California at Santa Barbara and the University of the Basque Country in Bilbao, Spain, describe their new device online in Nature.
“It’s terrific work in many respects, and is filled with valuable lessons for the quantum computing community,” says Daniel Lidar, a quantum-computing expert at the University of Southern California in Los Angeles.
The Google prototype combines the two main approaches to quantum computing. One approach constructs the computer’s digital circuits using qubits in particular arrangements geared to solve a specific problem. This is analogous to a tailor-made digital circuit in a conventional microprocessor made from classical bits.
Much of quantum computing theory is based on this approach, which includes methods for correcting errors that might otherwise derail a calculation. So far, practical implementations have been possible only with a handful of qubits.
The Google device is still very much a prototype. But Lidar says that in a couple of years, devices with more than 40 qubits could become a reality.
“At that point,” he says, “it will become possible to simulate quantum dynamics that is inaccessible on classical hardware, which will mark the advent of ‘quantum supremacy’.”
The new passive error correction circuit consists of just two primary qubits, in contrast to the 10 or more qubits required in most active approaches. The two qubits are coupled to each other, and each one is also coupled to a "lossy" object, such as a resonator, that experiences photon loss.
"In the absence of any errors, there are a pair of oscillating photon configurations that are the 'good' logical states of the device, and they oscillate at a fixed frequency based on the circuit parameters," Kapit explained. "However, like all qubits, the qubits in the circuit are not perfect and will slowly leak photons into the environment. When a photon randomly escapes from the circuit, the oscillation is broken, at which point a second, passive error correction circuit kicks in and quickly inserts two photons, one which restores the lost photon and reconstructs the oscillating logical state, and the other is dumped to a lossy circuit element and quickly leaks back out of the system.
The new method can correct photon loss errors at rates up to 10 times faster than those achieved by active, measurement-based methods. In addition, the passive method can partially suppress noise, so that there are fewer errors in the first place. In its current version, the method can correct only one error at a time, so if a second photon loss occurs before the correction is complete, the method cannot fix the resulting error.
Today, IBM unveiled an online service that lets anyone use the five-qubit quantum computer its researchers have erected at a research lab in Yorktown Heights, New York. You can access the machine over the Internet via a simple software interface—or at least it’s simple if you understand the basics of quantum computing.