How losing information can benefit quantum computing

Nov 24, 2013
This is an artist's conception of a NIST experiment showing how quantum computing might benefit from lost information. Two beryllium ions (red), used as quantum bits or qubits to store information, were "entangled" so that their properties were linked -- a useful feature for quantum computing. Two partner magnesium ions (green) released heat to the environment. Any unwanted information in the qubits was coupled to the outgoing heat, leaving the qubits in the desired entangled state (suggested by the hourglass). Credit: Bertram/Motion Forge

Suggesting that quantum computers might benefit from losing some data, physicists at the National Institute of Standards and Technology (NIST) have entangled—linked the quantum properties of—two ions by leaking judiciously chosen information to the environment.

Researchers usually strive to perfectly shield ions (charged atoms) in experiments from the outside world. Any "noise" or interference, including heat generated by the experiment and measurements that cause fragile quantum states to collapse, can ruin data and prevent reliable , the conventional approach to quantum information processing.

Turning bug into feature, a collaboration of physicists from NIST and the University of Copenhagen in Denmark decided to think and work outside the box. They cleverly linked the experiment to the outside world to establish and maintain the entanglement of two ions. Entanglement is a curious feature of the quantum world that will be necessary to process and transport quantum data or correct errors in future quantum computers.

The new research is described in a Nature paper posted online Nov. 24, along with similar work at Yale University using superconducting circuits.

"These new methods might be used to create entangled states that would be a resource in a traditional, logic-based quantum computer," NIST postdoctoral researcher John Gaebler says. "But there are also alternative architectures in which, for example, one couples a quantum computer to a specific noise environment and the resulting state of the computer contains the solution to the target problem."

The NIST experiments used two beryllium ions as quantum bits (qubits) to store quantum information and two partner magnesium ions, which were cooled with three ultraviolet laser beams to release heat.

The qubits were entangled by two beams and induced to "leak" any unwanted quantum states to the environment through continuous application of microwaves and one laser beam. The unwanted data were coupled to the outgoing heat in such a way that the qubits were left in only the desired entangled state—which happens to be the point of lowest motional energy, where no further heat and information is released to the environment.

Decay used to construct quantum information
This image shows the ion trap used in the experiment. Electrical potential are applied through thin gold wires on a chip and used to trap ions in a narrow slot. Credit: NIST

Unlike a logic operation, the process can be started from any state of the ions and still yield the same final state. The scheme also can tolerate some kinds of noise that might cause a traditional logic gate to fail. For instance, the lasers and microwaves had no negative effects on the target entangled state but reshuffled any unwanted states.

All operations applied at the same time quickly drove the two qubits into a specific entangled state and kept them in that state most of the time. The qubits approached the target state within a few milliseconds and were found to be in the correct 75 percent of the time. The qubit state deteriorated slightly over longer times as the qubits were disturbed by errant laser emissions. By applying about 30 repetitions of the four steps in a particular order, scientists boosted the success rate to 89 percent in a separate experiment.

Explore further: Physicists 'entangle' microscopic drum's beat with electrical signals

More information: Y. Lin, J.P. Gaebler, F. Reiter, T.R. Tan, R. Bowler, A.S. Sorensen, D. Leibfried and D.J. Wineland. Dissipative production of a maximally entangled steady state. Nature. Posted online Nov. 24, 2013.

Related Stories

On-chip quantum buffer realized

Nov 13, 2013

Nippon Telegraph and Telephone Corp. has realized a quantum buffer integrated on an optical waveguide. The buffer is based on the "slow light effect", where the propagation speed of a pulsed light in a special ...

Quantum world record smashed

Nov 14, 2013

A normally fragile quantum state has been shown to survive at room temperature for a world record 39 minutes, overcoming a key barrier towards building ultrafast quantum computers.

Two atoms entangled using microwaves for the first time

Aug 10, 2011

Physicists at the National Institute of Standards and Technology have for the first time linked the quantum properties of two separated ions (electrically charged atoms) by manipulating them with microwaves ...

Recommended for you

Could 'Jedi Putter' be the force golfers need?

2 hours ago

Putting is arguably the most important skill in golf; in fact, it's been described as a game within a game. Now a team of Rice engineering students has devised a training putter that offers golfers audio, ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

holoman
not rated yet Dec 18, 2013
Where is this all headed ?

http://colossalst...gled.htm

More news stories

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Could 'Jedi Putter' be the force golfers need?

Putting is arguably the most important skill in golf; in fact, it's been described as a game within a game. Now a team of Rice engineering students has devised a training putter that offers golfers audio, ...

Continents may be a key feature of Super-Earths

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Under some LED bulbs whites aren't 'whiter than white'

For years, companies have been adding whiteners to laundry detergent, paints, plastics, paper and fabrics to make whites look "whiter than white," but now, with a switch away from incandescent and fluorescent lighting, different ...