(Press-News.org) BOULDER, Colo.—Physicists at the National
Institute of Standards and Technology
(NIST) have for the first time coaxed two
atoms in separate locations to take turns
jiggling back and forth while swapping the
smallest measurable units of energy. By
directly linking the motions of two physically
separated atoms, the technique has the
potential to simplify information processing in
future quantum computers and simulations.
Described in a paper published Feb.
23 by Nature,* the NIST experiments enticed two beryllium ions (electrically charged
atoms) to take turns vibrating in an electromagnetic trap, exchanging units of energy, or
quanta, that are a hallmark of quantum mechanics. As little as one quantum was traded
back and forth in these exchanges, signifying that the ions are "coupled" or linked together.
These ions also behave like objects in the larger, everyday world in that they are
"harmonic oscillators" similar to pendulums and tuning forks, making repetitive, back-and-forth
motions.
"First one ion is jiggling a little and the other is not moving at all; then the jiggling
motion switches to the other ion. The smallest amount of energy you could possibly see is
moving between the ions," explains first author Kenton Brown, a NIST post-doctoral
researcher. "We can also tune the coupling, which affects how fast they exchange energy
and to what degree. We can turn the interaction on and off."
The experiments were made possible by a novel, one-layer ion trap cooled to minus
269 C (minus 452 F) with a liquid helium bath. The ions, 40 micrometers apart, float above
the surface of the trap. In contrast to a conventional two-layer trap, the surface trap
features smaller electrodes and can position ions closer together, enabling stronger
coupling. Chilling to cryogenic temperatures suppresses unwanted heat that can distort ion
behavior.
The energy swapping demonstrations begin by cooling both ions with a laser to
slow their motion. Then one ion is cooled further to a motionless state with two opposing
ultraviolet laser beams. Next the coupling interaction is turned on by tuning the voltages of
the trap electrodes. In separate experiments reported in Nature, NIST researchers
measured the ions swapping energy at levels of several quanta every 155 microseconds
and at the single quantum level somewhat less frequently, every 218 microseconds.
Theoretically, the ions could swap energy indefinitely until the process is disrupted by
heating. NIST scientists observed two round-trip exchanges at the single quantum level.
To detect and measure the ions' activity, NIST scientists apply an oscillating pulse
to the trap at different frequencies while illuminating both ions with an ultraviolet laser and
analyzing the scattered light. Each ion has its own characteristic vibration frequency; when
excited, the motion reduces the amount of laser light absorbed. Dimming of the scattered
light tells scientists an ion is vibrating at a particular pulse frequency.
To turn on the coupling interaction, scientists use electrode voltages to tune the
frequencies of the two ions, nudging them closer together. The coupling is strongest when
the frequencies are closest. The motions become linked due to the electrostatic
interactions of the positively charged ions, which tend to repel each other. Coupling
associates each ion with both characteristic frequencies.
The new experiments are similar to the same NIST research group's 2009
demonstration of entanglement—a quantum phenomenon linking properties of separated
particles—in a mechanical system of two separated pairs of vibrating ions (see
http://www.nist.gov/pml/div688/jost_060309.cfm). However, the new experiments coupled
the oscillators' motions more directly than before and, therefore, may simplify information
processing. In this case the researchers observed quantum behavior but did not verify
entanglement.
The new technique could be useful in a future quantum computer, which would use
quantum systems such as ions to solve problems that are intractable today. For example,
quantum computers could break today's most widely used data encryption codes. Direct
coupling of ions in separate locations could simplify logic operations and help correct
processing errors. The technique is also a feature of proposals for quantum simulations,
which may help explain the mechanisms of complex quantum systems such as high-temperature
superconductors.
In addition, the demonstration also suggests that similar interactions could be used
to connect different types of quantum systems, such as a trapped ion and a particle of light
(photon), to transfer information in a future quantum network. For example, a trapped ion
could act as a "quantum transformer" between a superconducting quantum bit (qubit) and
a qubit made of photons.
INFORMATION:
As a non-regulatory agency, NIST promotes U.S. innovation and industrial
competitiveness by advancing measurement science, standards and technology in ways
that enhance economic security and improve our quality of life.
* K.R. Brown, C. Ospelkaus, Y. Colombe, A.C. Wilson, D. Leibfried & D.J. Wineland. 2010. Coupled
quantized mechanical oscillators. Nature. Published online Feb. 23.
Quantum hot potato: NIST researchers entice 2 atoms to swap smallest energy units
New technique has potential to simplify future information processing
2011-02-24
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[Press-News.org] Quantum hot potato: NIST researchers entice 2 atoms to swap smallest energy unitsNew technique has potential to simplify future information processing