- Quantum Physics Used to Control Mechanical System
- Red in Jupiter’s Spot Not What Astronomers Thought
- Methane May Be Building Under Antarctic Ice
- Climate Quick Fix Could Create Toxic Algae Blooms
Posted: 17 Mar 2010 10:11 AM PDT
By using a quantum device to control a mechanical object, researchers have linked the mind-bending laws of quantum physics to the tangible, everyday world.
Until now, quantum physical behaviors were observed at atomic and subatomic scales, or in medium-sized molecules. Now they've been found in something that bumps and grinds, and can be seen by the naked eye.
"At the macroscopic scale we live in, we don't see quantum effects at all," said Andrew Cleland, a University of California, Santa Barbara physicist. "The goal of the experiment was to see if we could see quantum mechanical effects in a large, mechanical object."
The mechanical object used in the experiment, published March 17 in Nature and led by Cleland and fellow UCSB physicists John Martinis and Aaron O'Connell, is a tiny wafer of quartzlike material bracketed by metal plates. The wafer is a piezoelectric resonator, expanding and contracting in response to electrical voltages at a precise, extremely high frequency. Cleland likened its expansion and contraction to the inflation and deflation of a balloon.
The quantum device is a qubit, a term that generically refers to a kind of quantum transistor being used for quantum computation, in this case made from an ultrathin aluminum-based superconductor. At extremely cold temperatures, it goes quantum: It exists in an oscillating waveform spanning an excited state, an unexcited state, or both simultaneously, all controlled by electrical currents.
In a study published in September in Nature, Cleland's team coupled two qubits in what's known as quantum entanglement, in which the oscillations of one were linked to the oscillations of the other, even when physically distant. That feat drew attention for demonstrating quantum properties in a large, visible system, but the properties themselves still belonged to electrons, in which quantum effects are routinely observed and controlled.
In a sense, it was the same old quantum physics. The latest results occur in a new world, one that quantum physicists have tried to enter for nearly two decades. In a commentary accompanying the paper, University of Vienna physicist Markus Aspelmeyer described the reaction of an audience of physicists to whom Cleland described the experiment's design. "Dead silence — and then roaring applause," he recalled.
With their experiment, the researchers have not only fulfilled a two decade-old dream of controlling quantum motion in micro-meter sized system, but "opened the door for quantum control of truly macroscopic mechanical devices," wrote Aspelmeyer.
To do so, Cleland's team wired a qubit to a resonator, then cooled them to a fraction of a degree above absolute zero, the point at which all atomic motion nearly stops. At this temperature, the vibrations of the atoms in the qubit and resonator are small enough to prevent them from interfering with quantum measurements.
When the researchers sent a pulse of energy into the qubit, the resulting energy quantum was transferred to the resonator, which fluctuated accordingly. With extraordinarily acute vision, "you'd see it expanding and contracting. You'd see it vibrating. These are quantum vibrations," said Cleland.
One of the principles of quantum physics, illustrated by the Schrodinger's cat thought experiment, is that the act of measurement collapses an object's waveform into a single, observed state. To get around this conundrum, the researchers used a repetitive measurement, preparing the system and then measuring its waveform millions of times.
At a precise moment during one trial, the resonator might be both in its expanded and its contracted state; a single measurement forces it to "choose" which state to be in. The quantum nature of its behavior emerged from the accumulated readings. "If we do it enough times, we can assign a probability to the state at each point," said Cleland.
According to Aspelmeyer, the findings could inform the design of storage devices used in quantum computers. Cleland isn't sure the system will be reliable enough for that, but thinks it could be used in exploring how the subatomic rules of quantum physics are manifested at higher scales.
Schrodinger's cat experiment is likely impossible, because the cat itself is a measuring device, said Cleland. However, it might be possible with other large but inanimate objects linked to a quantum device.
"If you had a tuning fork and got it cold enough, maybe that could behave quantum mechanically," he said.
Image: Schematic of the resonator-qubit system./Nature
Citations: "Quantum ground state and single-phonon control of a mechanical resonator." By A. D. O'Connell, M. Hofheinz, M. Ansmann, Radoslaw C. Bialczak, M. Lenander, Erik Lucero, M. Neeley, D. Sank, H. Wang, M. Weides, J. Wenner, John M. Martinis & A. N. Cleland. Nature, March 18, 2010.
"The surf is up." By Markus Aspelmeyer. Nature, March 18, 2010.
Posted: 16 Mar 2010 03:26 PM PDT
The best thermal images of Jupiter's Great Red Spot yet captured have revealed surprising weather and temperature variation within the solar system's most famous storm.
The darkest red part of the spot turns out to be a warm patch inside the otherwise cold storm. The temperature variation is slight: "Warm" in this case translates to -250 degrees Fahrenheit while cold is an even frostier -256 degrees F. But even that difference is enough to create intriguing internal dynamics.
"This is our first detailed look inside the biggest storm of the solar system," said Jet Propulsion Laboratory astronomer Glenn Orton, who led the new study to be published in Icarus. "We once thought the Great Red Spot was a plain old oval without much structure, but these new results show that it is, in fact, extremely complicated."
The Red Spot has persisted since at least the late 17th century, when astronomers first spotted it. If you'd seen it back then, though, you might have been "tempted to call it the great red sausage," Orton said. "It's shrinking slowly." Still, it's the solar system's longest-lived and largest storm system, wider than three Earths.
Over the past few decades, astronomers had begun to get a handle on the weather patterns around the Great Red Spot, but not inside of it. Previous measurements have indicated that the spot towered over the surrounding cloud cover, much like supercells on Earth.
Scientists have also noticed that its color changes considerably, but what drives the changes — or the famous ruddy complexion in general — is unclear. A leading theory was that sulfurous molecules from deep in the Jovian atmosphere were being lofted by the storm, exposing them to ultraviolet radiation that would break them apart. The newly freed sulfur atoms would then change color and lend the area its distinctive tinge.
But that might not be the case. This latest work shows a clear correlation between the environmental conditions and color, but doesn't help the scientists figure out what chemistry is actually at work, Orton said.
"This is the first time we can say that there's an intimate link between environmental conditions — temperature, winds, pressure and composition — and the actual color of the Great Red Spot," Orton's collaborator, Leigh Fletcher, an Oxford astronomer added. "Although we can speculate, we still don't know for sure which chemicals or processes are causing that deep red color, but we do know now that it is related to changes in the environmental conditions right in the heart of the storm."
The new thermal images were captured by the VISIR instrument on the European Southern Observatory's Very Large Telescope in Chile.
Images: 1. ESO/NASA/JPL/ESA/L. Fletcher 2. JPL
Citation: "Thermal Structure and Composition of Jupiter's Great Red Spot from High-Resolution Thermal Imaging" in Icarus (forthcoming).
Posted: 16 Mar 2010 12:39 PM PDT
BALTIMORE — Microbes living under ice sheets in Antarctica and Greenland could be churning out large quantities of the greenhouse gas methane, a new study suggests.
In recent years scientists have learned that liquid water lurks under much of Antarctica's massive ice sheet, and so, they say, the potential microbial habitat in this watery world is huge. If the methane produced by the bacteria gets trapped beneath the ice and builds up over long periods of time — a possibility that is far from certain — it could mean that as ice sheets melt under warmer temperatures, they would release large amounts of heat-trapping methane gas.
Jemma Wadham, a geochemist at the University of Bristol in England, described the little-known role of methane-making microbes, called methanogens, below ice sheets on March 15 at an American Geophysical Union conference on Antarctic lakes.
Her team took samples from one site in Antarctica, the Lower Wright glacier, and one in Greenland, the Russell glacier. Trapped within the ice were high concentrations of methane, Wadham said, as well as methanogens themselves — up to 10 million cells per gram in the Antarctic sample and 100,000 cells per gram in Greenland. That's comparable to the concentration of methanogens found in deep-ocean sediments, she said. The species of microbes were also similar to those found in other polar environments, such as Arctic peat or tundra.
The team then put scrapings from both sites into bottles and incubated them with water to see which microbes might grow. For the Antarctic samples, Wadham said, "nothing happens for 250 days and then bam! You get tons of methane." The Greenland samples haven't been growing for as long and so far don't show much signs of giving off methane — but perhaps they just need more time, she reported at the meeting.
Other researchers have also recently found methanogens in icy settings. Mark Skidmore, a microbiologist at Montana State University in Bozeman, reported at the conference that his team has found methanogens in the Robertson glacier in the Canadian Rockies. "It underscores the importance of subglacial methanogenesis," Skidmore said.
The studies flesh out a picture of Antarctica as a much more dynamic and watery environment than the frozen, static one once envisaged. At least 386 lakes have been identified buried beneath the ice sheet, scientists from the University of Edinburgh reported at the meeting. Plans for major drilling projects are underway for several of them.
Images: 1) NASA. 2) Zina Deretsky/NSF.
Posted: 16 Mar 2010 11:41 AM PDT
Pouring iron into oceans may combat global warming by feeding carbon dioxide-gobbling algae, but those algal blooms could become fountains of neurotoxin.
According to a small-scale test, iron-enriched waters favor the growth of Pseudonitzschia, an algae that pumps out brain-damaging domoic acid.
"The toxin per cell increases, and there's an increased success against other species," said oceanographer William Cochlan of San Francisco State University, co-author of the study, published March 15 in the Proceedings of the National Academy of Sciences. Pseudonitzschia "is out there in the most pristine environments. They produce low levels of toxin, so they're not harmful. But if you add iron, and these cells proliferate, and produce more toxin per cell, then you have a problem."
Oceanic iron fertilization is one of many proposed, planet-scale engineering solutions to climate change. Others include shrouding Earth in sun-reflecting aerosol particles, manufacturing CO2-absorbing artificial trees, and pumping CO2 into underground reservoirs.
Critics say these geoengineering schemes are untested, unpredictable and could have disastrous consequences — if, that is, they even work. Proponents say geoengineering should at least be considered, if only as a last-ditch tactic. Both generally agree that more research is needed.
Iron-fertilization research, however, is caught in a catch-22. It's impossible to know large-scale effects without large-scale testing, but large-scale testing is limited by concerns about the effects.
The United Nations has declared a moratorium on oceanic iron-fertilization studies, and the International Maritime Organization has also limited research. But some companies and countries are pushing for restrictions to be lifted. In the case of a joint Indian-German expedition that fertilized 115 square miles of ocean in 2009, the restrictions have already been ignored.
The new report falls squarely into the middle of this fight.
"There's an absolute need for remedies involving carbon sequestration, but they have to have a scientific foundation. At this point, iron fertilization doesn't have that," said Cochlan.
Cochlan's team, led by University of Western Ontario phytoplankton specialist Charles Trick, added iron to tanks of water taken from the Gulf of Alaska, in an area where earlier researchers had conducted iron fertilization experiments.
They found that Pseudonitzschia, a common genus of algae, thrived on the iron. Pseudonitzschia at first accounted for a small fraction of algae and plankton in the water, but soon made up 80 percent of some tank populations.
Pseudonitzschia appears to benefit from its ability to produce domoic acid, which binds with iron and can then be reabsorbed by the algae. But unfortunately for other organisms, domoic acid is a potent toxin.
Cochlan, who previously studied a massive 2004 Pseudonitzschia bloom off the coasts of British Columbia and Washington, said the ecological consequences of an iron-fertilization-fed bloom could be profound, killing large numbers of animals and creating a steady injection of domoic acid into marine food chains, where it could accumulate in fish consumed by people. In humans, domoic acid produces permanent, short-term memory loss, and can even be fatal.
"Eventually, the toxicity subsides when the cells die. But doing a sustained iron enrichment experiment would mean that you'd want to keep these blooms going continuously," said Cochlan.
The researchers warned against drawing absolute conclusions from a small-scale study. But even if preliminary, the findings do suggest that researchers who've suggested that Pseudonitzschia could only bloom along coastlines, and not on the open sea, were wrong.
Later this month, scientists and policy experts will meet in Asilomar, California to discuss geoengineering risks and regulation. The meeting is organized by the Climate Response Fund, a nonprofit supporter of geoengineering research. Its director is Margaret Leinen, the former chief science officer of Climos, a San Francisco iron-fertilization company founded in 2005. Climos originally planned to sell fertilization-based carbon offsets, but after being criticized for jumping ahead of science has re-purposed itself as a research contractor.
"If domoic acid is produced by artificially stimulated ocean iron-fertilization blooms, it is likely produced during natural ones as well," Climos said in a statement March 15. "We need to understand exactly how deep-ocean phytoplankton respond to iron, be it naturally or artificially supplied, whether and in what situations domoic acid is produced, and how the ecosystem is or is not already adapted to this."
A key difference between natural and artificial iron supply is location, Cochlan said. There have not been any Pseudonitzschia blooms in the open ocean where iron fertilization is being considered.
"You're going to change the base of the food web," he said. "Going ahead with experiments like these without knowing what's up the chain is foolhardy."
Image: A 2004 Pseudonitzschia bloom off the Washington coast/NASA
Citation: "Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas." By Charles G. Trick, Brian D. Bill, William P. Cochlan, Mark L. Wells, Vera L. Trainer, and LisaD. Pickell. Proceedings of the National Academy of Sciences, Vol. 107 No. 11, March 16, 2010.
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