5/2/07

3:02 PMPage 276

SCIENCE
NEWSThis Week
isn’t such a strict connection between a gesture and an emotional context as there iswith [an ape’s] scream,” Pollick says.
Bonobos and chimpanzees are the two
closest evolutionary cousins to people. The
human lineage diverged from the bonobochimpanzee lineage about 6 million years
ago, and the last common ancestor of bonobos and chimps lived about 2.5 million years
ago. Any similarities in how the two ape
species use hand gestures were probably
inherited from that common ancestor, giving scientists a window into the past.
“I think this is the best kind of evidence
that you’ll find” for how language evolved,
comments Susan Goldin-Meadow, whostudies human gesture and language at theUniversity of Chicago. Fossils reveal almost
nothing about how people’s distant ancestors communicated, so scientists can infer
the past only by looking at modern humans
and other primates, she says.
For example, all apes use hand motions
to communicate, but monkeys and otheranimals don’t. And gestures are ubiquitousin human communication. “In every single
culture, we gesture as we talk,” GoldinMeadow says.
Scientists don’t agree on whether andhow gestures influenced the evolution oflanguage. For example, Goldin-Meadow
suggests that hand motions could havedeveloped in parallel with vocal sounds
rather than coming first. —P. BARRY

Quantum
Loophole
Some quirks of physics
can be good for science
Quantum theory notoriously sets limits on

how precisely we can make measurements.
But the quirks of the quantum realm canalso be turned to advantage. Physicists have
now demonstrated a way to almost double
measurement precision when using photons to gauge distances.
Like markings on a ruler, the orderly
waves of laser light can be used to measurelengths. In an interferometer, a laser beamis split into two beams that take two different paths. The beams bounce off mirrors
and converge at the other end of the instrument, where their crests and troughs add
together or cancel, depending on how thesefeatures line up. The resulting interference276

M AY 5 , 2 0 0 7VOL. 171

ENHANCED VISION Four photons fed into an interferometer in pairs at the two entry points(A) split and form entangled quadruplets circulating in opposite directions, bouncing off mirrors(gray disks). The interference pattern that the photons produce (in the green box at left)
precisely reveals the thickness of a glass plate (small square at right).

pattern reveals tiny differences in how far
the two beams traveled. For example, asmall displacement of one mirror will cause
the interference pattern to shift.
The precision of such a measurement
depends on the wavelength of the light used.
In the 1990s, physicists proposed that they
could improve the sensitivity of interferometers by employing sets of photons in thesame quantum state, or entangled, as if they
formed a molecule of light. When several
photons are coaxed into such molecules,
the scientists predicted, an interferometer
would respond as if the combined photons
had a wavelength smaller than that of theindividual photons.
Physicists first demonstrated the effectwith pairs of photons in 2002. That strategy
could increase sensitivity by about 40 percent
over the sensitivity of two nonentangled protons.
A Japanese-British team has now doneeven better using four photons at a time.
In their setup, the physicists feed the twopairs into an interferometer. Each photon
then splits, taking two paths simultaneously in what’s called a quantum superposition of states. The result is one set offour photons forming an entangled statethat circulates around the interferometerin one direction, accompanied by anotherentangled quadruplet circulating in theother direction.
Each four-photon set, acting as a single
quantum persona, “behaves as if it had ashorter wavelength,” says team member
Jeremy O’Brien of the University of Bristol
in England. This is potentially like using aruler with spacing four times as fine, heexplains. In the case of four nonentangled
photons, the improvement over using a single photon is only twofold.
In their experiment, the researchersarranged for one of the paths to cross aglass plate, which has the same effect asaltering the length of the path. Interference between the two entangled states
measured that length difference with theexpected increase in precision. The resultsappear in the May 4 Science.
Paul Kwiat of the University of Illinois
at Urbana-Champaign says that this experiment is an interesting demonstration, butthat to get dramatic improvements, physicists would need to get many more photons
to cooperate. “We don’t yet know how tomake sources that have [a quadrillion]
entangled photons,” he says.
Jonathan Dowling of Louisiana State
University in Baton Rouge says that thefour-photon method could be useful insome applications, such as using laser lightto etch circuits on computer chips to provide features smaller than those that canbe achieved now. —D. CASTELVECCHI

AutomaticNetworking
Brain systems charge up
in unconscious monkeys
Anesthetized monkeys may be dead to

the world, but their brains remain surprisingly lively. Organized patterns ofSCIENCE NEWSN. TOMOHISA/SCIENCE

FOBs 5-5