Atoms queue up for quantum computer networks

The experiment is carried out in a glass cell with very low pressure. In here is an ultra-thin glass fiber and a gas of cesium atoms. Using lasers and a magnetic field, the atoms are cooled down to almost absolute zero (minus 273 degrees Celsius) and the atoms gather as a cloud around the glass fiber. Then two laser beams with very different frequencies are transmitted into the fiber, thereby capturing atoms above the fiber surface. By measuring the difference in the speed of light for two other light beams on each side of the atoms' absorption line, you can measure the number of atoms.
Credit: Ola Jakup Joensen, Niels Bohr Institute

In order to develop future quantum computer networks, it is necessary to hold a known number of atoms and read them without them disappearing. To do this, researchers from the Niels Bohr Institute have developed a method with a trap that captures the atoms along an ultra thin glass fiber, where the atoms can be controlled. The results are published in the scientific journal, Physical Review Letters.

The research is carried out in the quantum optics laboratory in the basement of the Niels Bohr Institute in Copenhagen. The underground laboratory is set back from the road so there are no vibrations from traffic. Here, the researchers have designed experiments in which they can perform ultrasensitive trials with quantum optics.

"We have an ultra-thin glass fiber with a diameter of half a micrometer (a hundred times smaller than a strand of hair). Along this glass fiber we capture cesium atoms. They are cooled down to 100 micro Kelvin using a laser -- this is almost absolute zero, which is equivalent to minus 273 degrees Celsius. This system acts like a trap that holds the atoms on the side of the glass fiber," explains Jürgen Appel, Associate Professor in the research group Quantop at the Niels Bohr Institute, University of Copenhagen.

Atoms and light linked together

When light is transmitted through the glass fiber thread, the light will also move along the surface because the fiber is thinner than wavelength of the light. This creates strong interaction between the light and the atoms sitting securely above the surface of the fiber.

"We have developed a method where we can measure the number of atoms. We send two laser beams with different frequencies through the glass fiber. If there were no atoms on the fiber, the speed of light would be the same for both light beams. However, the atoms affect the two frequencies differently and by measuring the difference in the speed of light for the two light beams on each side of the atoms' absorption lines, you can measure the number of atoms along the fiber. We have shown that we can hold 2,500 atoms with an uncertainty of just eight atoms," says Jürgen Appel.

These are fantastic results. Without this method, you would have to use resonant light (light that the atoms absorb) and then you would scatter photons, which would kick the atoms out of the trap, says Jürgen Appel and explains that with this new method they can measure and control the atoms so that only 14 percent are kicked out of the trap and are lost.

"Our resolution is only limited by the natural quantum noise (the laser light's own minimal fluctuations) so our method could be used for so-called entangled states of atoms along the fiber. Such an entangled system with strongly interacting atoms and light is of great interest for future quantum computer networks," notes Jürgen Appel.

Source: University of Copenhagen - Niels Bohr Institute

Plants return to Earth after growing in space

Astronaut Reid Wiseman injected a fixative solution onto the seedlings. Credit: NASA

Researchers at Simon Gilroy's lab in the Department of Botany at the University of Wisconsin-Madison this afternoon greeted a truck carrying small containers holding more than 1,000 frozen plants that germinated and grew aboard the International Space Station.

On Tuesday, when Gilroy's team inspected the plants at the Kennedy Space Center in Florida, they saw exactly what they wanted: Petri dishes holding seedlings that sprouted and grew in weightlessness.

After their arrival in Madison, the plants went directly into a deep freeze. After being thawed in a few months, they will donate their RNA to an instrument that will measure the activity of all of their approximately 30,000 genes.

Half of the plants will become subjects in Gilroy's longstanding exploration of the genetic control of the proteins that enable plants to grow in zero gravity. "Gravity is a fantastically pervasive force that affects all biology," says Gilroy. "One astronaut observed that plants get lazy in a weightless environment; they grow long and thin, and don't lay down strong material, just like people lose bone mass in space because it isn't needed for supporting weight."

The other half of the experiment represents a departure for Gilroy, and for NASA, the agency supporting this area of space research. After these plants undergo a similar genetic analysis at UW-Madison's Biotech Center, the data will get an initial check-over from Gilroy's group. And then a treasure trove of digital data on plant genetic activity in microgravity will be made available to any researcher interested in mining it.

"Access to space is very rare," Gilroy says. "Traditionally, a research group will put an experiment in space, get the results and publish. But NASA is trying a new mode, called geneLAB, where the research group will put organisms in space, then, as soon as possible, release the raw data to anyone who wants to analyze it. They hope it will speed up major advances on these tiny samples that we can afford to place in space. I see this as open-source science."

Through the process called transcription, genes produce RNA that becomes the template for proteins, and in both sets of experiments, the RNA data will show which genes become more or less active in microgravity, when compared to an identical set of plants grown on Earth.

While Gilroy plans to focus on structural proteins, the geneLAB experiment compares four variants of Arabidopsis called ecotypes. "This data should provide a broad field of investigation -- far more than one lab can handle," Gilroy says. "We are going to end up with an enormous amount of transcription data. We will do some initial work to check the major genes which go up or down, but there's tremendous potential for further analysis by other labs around the world."

But while the geneLab approach sounds promising, Gilroy concedes that it carries no guarantees. "This may be a path forward in crowd-sourcing science. At the least, as a single lab we could never analyze this data as fully as many labs around the world all working with it."

The "Biological Research in Canister" containers that held these experiments on board the space station were designed, tested and operated according to NASA's rigorous approach, Gilroy says. "Each project represents an enormous investment, and you really want everything to go perfectly. You become one of the most careful scientists in the world. You test everything, make duplicates, and are always considering what may go wrong so you can do another test."

NASA is an unfamiliar world to most botanists, but Gilroy seems to be enjoying every step of the way, and has even learned the organization's peculiar parlance. "At first, talking in acronyms is very strange," he says, "and you can't understand anything when NASA people start going into NASA-speak. But once you get into it, you catch yourself doing the exact same thing."

In the microgravity experiments, Gilroy is exploring the genetic basis of a phenomenon known to gardeners and horticulturalists for many years. Plants that grow up without mechanical stresses -- due to wind, rain or other disturbances -- "are much more susceptible to pests, are not as robust," Gilroy says, "but if you go into a greenhouse and shake the plants, they grow up more compact, strong, and resistant to stress. They are even more resistant to plant diseases."

It turns out that the same signaling system used to detect mechanical stresses like gravity is also used to defend against pathogens. That may explain why plants in space appear more susceptible to disease.

That overlap raises the stakes for understanding the impact of gravity on plants beyond the notion of building stronger crops that can stand up in the field. Understanding the signals could help in the never ending battle against plant disease.

Likewise, NASA has its own practical interest in the research: Plants will supply food and oxygen for long-distance space travel, and keeping them healthy will be a matter of life and death. "If you are growing plants as part of a human life support system," Gilroy says, "you'd rather not have them suddenly die."

Source: University of Wisconsin-Madison

The science behind swimming: From whales to larvae, common principles at work in swimming

Whale and diver (stock illustration). Using simple hydrodynamics, researchers were able to show that a handful of principles govern how virtually every animal -- from the tiniest fish to birds to gigantic whales propel themselves though the water. Credit: © James Thew / Fotolia

At nearly 100 feet long and weighing as much as 170 tons, the blue whale is the largest creature on the planet, and by far the heaviest living thing ever seen on Earth. So there's no way it could have anything in common with the tiniest fish larvae, which measure millimeters in length and tip the scales at a fraction of a gram, right?

Not so fast, says L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics.

Using simple hydrodynamics, a team of researchers led by Mahadevan was able to show that a handful of principles govern how virtually every animal -- from the tiniest fish to birds to gigantic whales propel themselves though the water. The study is described in a September 14 paper in Nature Physics.

"What we wanted to investigate was how the speed of an organism changes as a function of how large it is, how quickly it moves and how much it moves," Mahadevan said. "To resolve that in detail, however, is very complex, because there is a great deal of differences in morphology and what parts of the body different creatures use to swim. The question is: Is there anything in common across all these organisms? The answer, we found, is yes."

In an effort to uncover those common principles, Mahadevan working with a postdoctoral fellow in his group , Mattia Gazzola, and a colleague Mederic Argentina from the University of Nice, began by trying to unpack the physics of how different creatures swim.

"The traditional approach to swimming phenomena is to take a certain specimen and accurately characterize it via experiments and/or simulations, and try to generalize from there, but it is very hard to strip out specific biological effects from general principles," Gazzola said. "We instead thought that while swimmers exhibit a huge diversity in shapes and kinematics, at the end of the day they all live in the same media, water.

"Therefore we thought that if a unifying mechanistic principle existed, it had to lie in the constraints that the flow environment poses to all its inhabitants," he continued. "And this is a purely physical problem, much easier to solve since it is not affected by biological vagaries. What I like about this paper is that in one line of algebra we derived a compact formula that accounts for 50 years of experiments. This is an example of how powerful minimal modeling can be."

"The basic relationship we wanted to understand was how the input variables -- namely the size of the organism, the amount an organism moves and how quickly it moves -- control the output variable, which is effectively the speed at which it moves," Mahadevan explained. "What we found is that there is a specific relationship, which can be described by in terms of a simple scaling law with two limits."

The first, which corresponds to creatures moving at intermediate speeds, describes situations where the bulk of the resistance is caused by skin friction, because water "sticks" to the organism's body. At faster speeds, Mahadevan said, the resistance organisms face largely comes from pressure that builds up in front of and around them, which is described by the second limit.

"While it wasn't a surprise that the resistance changed at organisms moved faster, the fact that those challenges could be so simply described was interesting and provocative, because we are talking about organisms that range in size from a few millimeters to the size of a blue whale," Mahadevan said.

Armed with those observations, Mahadevan and colleagues turned to a host of empirical observations that had been made over the past 50-plus years. When those data were plotted on a graph, the researchers found that the swimming speed of virtually every organism, from fish larvae to frogs to birds, amphibians and even whales, could be described by one of the two equations.

The same also held true, Mahadevan said, when Gazzola created complex computer models to solve the governing equations of fluid dynamics to describe how different organisms swim.

"What is particularly interesting is that all the organisms essentially reach the hydrodynamic limits of performance," he said. "Our simple theory, which doesn't distinguish in any detailed way between something like a blue whale and fish larvae, except in the parameters of how large you are, much you move and how quickly you move, can describe all this diversity. That suggests there are general principles at work here."


Source: Harvard University