Scientists use 'voting' and 'penalties' to overcome errors in quantum optimization

Feb 06, 2014

Seeking a solution to decoherence—the "noise" that prevents quantum processors from functioning properly—scientists at USC have developed a strategy of linking quantum bits together into voting blocks, a strategy that significantly boosts their accuracy.

In a paper published today in Nature Communications, the team found that their method results in at least a five-fold increase in the probability of reaching the correct answer when the processor solves the largest problems tested by the researcher, involving hundreds of qubits.

The team, led by Daniel Lidar—director of the USC-Lockheed Martin Quantum Computing Center at the USC Viterbi School of Engineering—ran their tests on the 512-quantum-bit D-Wave Two processor. The D-Wave Two is among the first commercially available quantum processors, a device so advanced that there are only two in use outside the Canadian company where they were built: The first one went to USC and Lockheed Martin, and the second to NASA and Google.

"We have demonstrated that our quantum annealing correction strategy significantly improves the success probability of the D-Wave Two processor on the benchmark problem of antiferromagnetic chains, and are planning to next use it on computationally hard problems," Lidar said. His team includes graduate student Kristen Pudenz and postdoctoral fellow Tameem Albash.

Lidar added that all quantum are expected to be highly susceptible to decoherence, so that error correction is viewed as an essential and inescapable part of .

Quantum processors encode data in qubits, which have the capability of representing the two digits of one and zero at the same time – as opposed to traditional bits, which can encode distinctly either a one or a zero. This property, called superposition, along with the ability of quantum states to "interfere" (cancel or reinforce each other like waves in a pond) and "tunnel" through energy barriers, is what may one day allow quantum processors ultimately perform optimization calculations much faster than traditional processors.

Decoherence knocks qubits out of superposition, forcing them to behave as traditional bits, and robbing them of their edge over traditional processors.

Pudenz, Albash and Lidar developed and tested a strategy of grouping three qubits together into larger blocks of encoded qubits that can be decoded by a "majority vote." This way, if decoherence affects one of the qubits and causes it to "flip" to the incorrect value, the other two qubits in the block ensure that the data is still correctly encoded and can be correctly decoded by out-voting the errant .

These voting blocks of qubits are then magnetically tied to a fourth qubit in such a way that if any one "flips" then all four must flip. In effect, it makes the whole block of four so massive that it's difficult for one lonely qubit acting under the influence of decoherence to throw a wrench in the works.

Explore further: New research signals big future for quantum radar

More information: Paper: www.nature.com/ncomms/2014/140… full/ncomms4243.html

Related Stories

Large-scale quantum chip validated

Jun 28, 2013

A team of scientists at USC has verified that quantum effects are indeed at play in the first commercial quantum optimization processor.

Quantum computer built inside a diamond

Apr 04, 2012

Diamonds are forever – or, at least, the effects of this diamond on quantum computing may be. A team that includes scientists from USC has built a quantum computer in a diamond, the first of its kind to include protection ...

Advancing quantum computing

May 30, 2012

European researchers have made important advances in understanding the major stumbling block to realisation of quantum computers, a phenomenon known as decoherence.

D-Wave sells first commercial quantum computer

Jun 01, 2011

(PhysOrg.com) -- Last week, Burnaby, British Columbia-based company D-Wave Systems, Inc., announced that it sold its first commercial quantum computer. Global security company Lockheed Martin, based in Bethesda, ...

Recommended for you

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

Precision gas sensor could fit on a chip

Feb 27, 2015

Using their expertise in silicon optics, Cornell engineers have miniaturized a light source in the elusive mid-infrared (mid-IR) spectrum, effectively squeezing the capabilities of a large, tabletop laser onto a 1-millimeter ...

A new X-ray microscope for nanoscale imaging

Feb 27, 2015

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

New research signals big future for quantum radar

Feb 26, 2015

A prototype quantum radar that has the potential to detect objects which are invisible to conventional systems has been developed by an international research team led by a quantum information scientist at the University ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.