Physicists Successfully Store and Retrieve Nothing

t sounds like a headline from the spoof newspaper The Onion, but for physicists, this is actually an achievement: Two teams have stored nothing in a puff of gas and then retrieved it a split second later. Storing a strange form of vacuum builds on previous efforts in which researchers stopped light in its tracks (ScienceNOW, 22 January 2001) and may mark a significant step toward new quantum information and telecommunication technologies.

To stop light, researchers first shine an intense and continuous beam of laser light into a gas of atoms. That "control beam" tickles the atoms to allow a pulse of laser light of another wavelength to enter the gas. To trap the pulse, researchers turn off the control beam, which causes the pulse to imprint itself on the atoms. To release it again, they turn on the control laser.

So storing a vacuum might sound ridiculously simple: Follow the same procedure but leave out the pulse, and you store nothing. However, Alexander Lvovsky of the University of Calgary in Canada and his colleagues and Mikio Kozuma of the Tokyo Institute of Technology in Japan and his group have stored a very peculiar type of nothingness called a "squeezed vacuum."

To see what this is, begin with a normal light wave. Classically, this is a smooth wave of electromagnetic fields with equally spaced peaks and dips. But throw in quantum mechanics and things get more complicated. The precise height of the wave becomes uncertain, so the wave gets fuzzy (see figure). Physicists have learned how to manipulate that inevitable uncertainty--for example, making it smaller at the peaks and larger in between. That makes "phase-squeezed light." Now imagine turning down the intensity of the phase-squeezed light to zero. The wave itself goes away, but the waxing and waning uncertainty remains, creating a squeezed vacuum.

This is what Lvovsky and Kozuma stored. To make a pulse of squeezed vacuum, both used a device called an optical parametric amplifier, the heart of which is a crystal whose optical properties can be controlled by laser light. Kozuma and colleagues stored pulses of squeezed vacuum for up to 3 microseconds in rubidium atoms chilled to near absolute zero, they report in a paper to be published in Physical Review Letters. Lvovsky and colleagues stored their pulses for 1 microsecond in warm rubidium gas and say they reconstructed the squeezed vacuum in greater detail. Their results will appear in the same journal.

Proving that the squeezed vacuum survived its confinement is tricky, as it's hard to measure nothing. To probe the retrieved vacuum, researchers "mixed" it with the same ordinary laser light that was used to excite the optical parametric amplifier and make the squeezed vacuum. They then observed the telltale up and down in the uncertainty in that light beam, which was effectively transferred from the resurrected vacuum.

"I'm very impressed," says physicist Alexander Kuzmich of the Georgia Institute of Technology in Atlanta. "It's a real technical achievement." The ability to store squeezed states could help pave the way to new types of quantum networks that would carry uncrackable coded messages, says Kuzmich, who in 2006 stored and retrieved a single photon. More conceptually, such experiments might help spell out the boundary between the quantum and classical realms, he says. "There is something we still don't understand about that transition."

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'Northern lights lab' switched on

Aurora observatory opens on remote Arctic island.

SVALBARD For many people, living through the murky twilight of a polar winter would be a depressing experience. But not for the scientists working at a new observatory on the remote Norwegian island of Svalbard. For them, the Arctic darkness gives them the perfect view of the aurora borealis, also known as the northern lights.

These mysterious swirls of light, visible in the polar sky, are caused when superfast particles spat out by the Sun's nuclear inferno hit our atmosphere, causing atoms high in the sky to give off a ghostly glow. These aurorae are only visible in polar regions because the Sun's particles are channelled along the Earth's magnetic field lines, which emerge roughly from Earth's poles. Because they occur at altitudes of more than 80 kilometres, studying them requires very sensitive optical instruments, and a decent vantage-point far from any light pollution.

The new Kjell Henriksen Observatory, perched at the top of the Advent Valley outside Svalbard's largest settlement, Longyearbyen, offers just that. Svalbard provides "a window into space", says Fred Sigernes, an atmospheric researcher at the University Centre in Svalbard, which runs the new observatory. It joins several other facilities that already study the northern lights.

Opened last week by Norway's higher-education minister, Tora Aasland, the new observatory currently houses instruments from 16 institutions in 7 countries. "There are facilities for all sorts of people and instruments," says Dag Lorentzen, also from the University Centren in Svalbard. The instruments are mainly optical, because the aurora borealis gives off visible light.

The observatory will be one of the few places on Svalbard that will be at its busiest during the winter months, says Lorentzen. Though some work has already begun, the main optical telescope will be installed this summer; so the real action will begin next winter, when researchers will be observing the dark skies around the clock.

Northern dark

From late October onwards, Svalbard, at a latitude of about 78º North, is plunged into round-the-clock darkness. Now, in late February, it is only two weeks since the official 'polar dawn', and by mid-morning still only the mountaintops are tinged with the Sun's tentative pinkish rays. Down in Longyearbyen, the light, reflected off the snowy slopes, has an eerie bluish tinge — the town will not see direct sunlight for a few days yet.

The researchers at the observatory have a fairly unorthodox commute to work. The journey from Longyearbyen involves driving along the wide glacial Advent Valley to Mine no. 7 — Svalbard's only still-functioning coal mine. From there, the observatory is reached in army-surplus vehicles, which bump and rumble up the frozen slopes on caterpillar treads.

So sensitive are the instruments at the observatory that visitors are not even allowed to use headlights when driving up the hillside, and all communal areas within the observatory have heavy shutters on their windows.

Once at the observatory, access to the building is currently through the back door, as the main entrance is under 2 metres of snow. But they're prepared for poor weather. They have 10 tonnes of backup batteries for power emergencies, and several rooms full of bunk beds for sleeping in the event of storms. Lorentzen and his colleagues have already done an 18-day stint at the observatory, while waiting for the right conditions to launch a radar rocket into the atmosphere to collect data on the chemicals given off when the aurora lights are produced.

On the day side

Ironically, Svalbard's long polar night will also allow researchers to study what are often referred to as the 'dayside aurora'. The most commonly visible northern lights are the 'nightside aurora', which occur when solar-wind particles are 'slingshotted' around by Earth's magnetic field and enter the atmosphere on the side of Earth facing away from the Sun. That's why northern lights are typically visible at night.

But during the noon darkness of Svalbard's winter, observers should be able to see the dayside aurora, which enter our atmosphere directly. Without the extra slingshot magnetic kick, these particles are less energetic, so produce a fainter, reddish glow.

The observatory's researchers hope that their data could soon help to answer more general questions about solar weather, of which the northern lights are just one side-effect. Large solar storms, which produce spectacular auroral displays, can also knock out communications satellites, force planes to be diverted, and mess up your in-car global positioning system. The Sun is currently in the weakest phase of its 11-year activity cycle — within a few years, such solar flare-ups are set to become more common.

It may even be possible, one day, to harvest the immense energy outbursts behind the northern lights, Lorentzen says, although he admits that currently we have no idea how. "All we know is that it is a lot of energy," he says.

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Physics lab completes world's largest jigsaw puzzle

By Stephanie Nebehay

GENEVA (Reuters) - A 100-tonne wheel, the last piece of an ambitious experiment that scientists hope will help unlock the secrets of the universe, was successfully lowered into an underground cavern on Friday.

It is the final major element in the ATLAS particle detector, the largest of four detectors being hooked up to the world's most powerful particle accelerator which the European Organisation for Nuclear Research (CERN) hopes to start up around the middle of 2008.

"This last piece completes this gigantic puzzle," CERN said in a statement.

The wheel was lowered down a 100-metre shaft and aligned within a millimeter of other detectors at CERN, the world's leading centre for particle research located at a sprawling complex along the Swiss-French border.

The ATLAS detector will measure particles called muons expected to be produced in particle collisions in the accelerator, known as the Large Hadron Collider (LHC).

The LHC will recreate conditions just after the Big Bang, which many scientists believe gave birth to the universe, by colliding two beams of particles at close to the speed of light.

"As particles pass through a magnetic field produced by superconducting magnets, this detector has the ability to accurately track them to the width of a human hair," CERN said.

Experiments at the LHC, which lies in an underground tunnel measuring 17 milesin circumference, should allow physicists to take a big leap on a journey that began with Isaac Newton's law of gravity, it said.

Science has been unable to explain fundamental questions such as how particles acquire mass. The experiments will also probe the mysterious dark matter of the universe and why there is more matter than antimatter.

"Soon the first protons will be smashed together and the secrets of our universe will begin to unravel," CERN said.

CERN spokesman James Gillies said: "We know about 4 percent of the universe. The LHC might teach us about what the remaining 96 percent of the universe is made of, what cosmologists call dark matter."

Once the LHC starts running, it is likely to take a year for "new physics" to emerge, he said. Useful science is expected to continue unfolding for up to 20 years.

Some 10,000 scientists from around the world have worked on the complex apparatus since construction began in 1994.

The majority, some 6,000, are from CERN's 20 European member states although Americans are the largest single nationality (1,000), followed closely by Russians, according to Gillies.

Before the LHC can be started up, some 38,000 tonnes of equipment must be cooled to minus 456 degrees Fahrenheit for the magnets to operate in a superconducting state. This is done using many tonnes of liquid nitrogen and liquid helium.

"That is actually colder than outer space. It is a very big task," Gillies said. "It's essentially how a refrigerator works, it is just an extraordinarily large one and the temperature is incredibly cold."

(Editing by Robert Woodward)

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