Freedawn Scientia

Thursday, 5 February 2015

Hubble captures rare triple moon transit of Jupiter

These new NASA/ESA Hubble Space Telescope images capture a rare occurrence as three of Jupiter’s largest moons parading across the giant gas planet’s banded face. Hubble took a string of images of the event which show the three satellites—Europa, Callisto and Io—in action.

These new NASA/ESA Hubble Space Telescope images capture a rare occurrence as three of Jupiter’s largest moons parade across the giant gas planet’s banded face.The image on the left shows the Hubble observation at the beginning of the event. On the left is the moon Callisto and on the right, Io. The shadows from Europa, which cannot be seen in the image, Callisto, and Io are strung out from left to right.The image on the right shows the end of the event, approximately 42 minutes later. Europa has entered the frame at lower left with slower moving Callisto above and to the right of it. Meanwhile Io — which orbits significantly closer to Jupiter and so appears to move much more quickly — is approaching the eastern limb of the planet. Whilst Callisto’s shadow seems hardly to have moved Io’s has set over the planet’s eastern edge and Europa’s has risen further in the west. Credit: NASA, ESA, Hubble Heritage Team

There are four Galilean satellites—named after the 17th century scientist Galileo Galilei who discovered them [1]. They complete orbits around Jupiter ranging from two to seventeen days in duration. The moons can commonly be seen transiting the face of Jupiter and casting shadows onto its layers of cloud. However, seeing three of them transiting the face of Jupiter at the same time is rare, occurring only once or twice a decade.

The image on the left shows the Hubble observation at the beginning of the event. On the left is the moon Callisto and on the right, Io. The shadows from Callisto, Io and Europa are strung out from left to right. Europa itself cannot be seen in the image.

The image on the right shows the end of the event, just over 40 minutes later. Europa has entered the frame at lower left with slower-moving Callisto above and to the right of it. Meanwhile Io—which orbits significantly closer to Jupiter and so moves much more quickly—is approaching the eastern limb of the planet. Whilst Callisto’s shadow seems hardly to have moved, Io’s has set over the planet’s eastern edge and Europa’s has risen further in the west. The event is also shown from start to finish in a video.

Missing from this sequence is the Galilean moon Ganymede which was outside Hubble’s field of view.

The moons of Jupiter have very distinctive colours. The smooth icy surface of Europa is yellow-white, the volcanic sulphur surface of Io is orange and the surface of Callisto, which is one of the oldest and most cratered surfaces known in the Solar System, is a brownish colour.

The images were taken with Hubble’s Wide Field Camera 3 in visible light on 23 January 2015. Whilst Hubble captures these moons in great clarity they can also be seen with a small telescope or even a decent pair of binoculars. Why not try it at home?

– Credit and Resource –

ESA / NASA

Hubble captures rare triple moon transit of Jupiter

Wednesday, 4 February 2015

In The Life of a Polar Bear

If I was forced to choose a favorite type of bear, I would have to go with the incredible Polar Bear. These animals are furocious, gracefull, resilliant, terrifying and cute all wrapped up in a white fluffy coat….or are they? White fluffy coat I mean.

For those that agree that the Polar Bear is a truly awesome animal, this page is dedicated to them, enjoy

General Information on Polar Bears

The polar bear (Ursus maritimus) is a carnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is a large bear, approximately the same size as the omnivorous Kodiak bear (Ursus arctos middendorffi).

A male adult polar bear, also known as a Boar, weighs around 350–700 kg, while a sow (adult female) is about half that size.

Although it is the sister species of the brown bear, it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet. Although most polar bears are born on land, they spend most of their time at sea. Their scientific name means “maritime bear”, and derives from this fact. Polar bears hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present.

The polar bear is classified as a vulnerable species, with eight of the nineteen polar bear subpopulations in decline. For decades, large scale hunting raised international concern for the future of the species but populations rebounded after controls and quotas began to take effect. For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and polar bears remain important in their cultures.

Polar Bear Stats

Scientific name: Ursus maritimus
Rank: Species
Higher classification: Ursus
Mass: 150 – 250 kg (Adult, Female), more
Speed: 10 km/h (Adult, Swimming), 5.6 km/h on average (Adult, Walk)
Height: 1.22 – 1.6 m (Adult, At Shoulder), 1.33 m on average (Adult, At Shoulder, Male)
Length: 1.8 – 2.4 m (Adult, Female), 2.4 – 3 m (Adult, Male)

Information on Polar Bears

Habitat

Polar bears live in countries that ring the Arctic Circle: Canada, Russia, the United States (in Alaska), Greenland and Norway. In the winter, temperatures in the Arctic are usually around minus 29 degrees Fahrenheit (minus 34 degrees Celsius) and can reach as low as minus 92 F (minus 69 C). The temperature of the water is frigid, as well, reaching as low as 28 F (minus 2 C), the freezing point of seawater, according to PBS Nature.

Polar bears are excellent swimmers; their scientific name, Ursus maritimus, means “sea bear,” according to the San Diego Zoo. They use their big front feet to paddle and their back legs as rudders. These bears have been known to swim more than 60 miles (100 km) without rest.

Polar bears are solitary. The animal will spend its days sitting on the ice by a seal breathing hole, waiting for one to pop up. This style of hunting is called still-hunting. Polar bears will also seek out seal lairs, crash through the roof and kill the seals inside.

Unlike other bears, polar bears do not hibernate in the winter, according to the San Diego Zoo. They continue to hunt, unless the weather is extremely cold. Then they may seek shelter in a snow den.

Diet

The polar bear’s primary food source is seals. Their diet of meat makes them carnivores. If the food supply is plentiful, they will only eat seal blubber. This high-calorie meal helps the bears build up fat reserves, which keep polar bears healthy between feedings and help maintain their body temperature. According to PBS Nature, polar bears need 4.4 lbs (2 kg) of fat each day. This is equal to about 121 lbs. of seal (55 kg) and provides about eight days’ worth of energy.

If seal hunting isn’t going well, polar bears will also eat anything they can find, such as fish, eggs, vegetation, reindeer, rodents, birds, berries and human garbage.

Offspring and Mating

Females usually give birth during the months of November or December, after a gestation of eight months. In preparation, the animals dig a cave from a snow bank in which to have their cubs. This cave is called a maternity den.

A female polar bear typically gives birth to twins, though singles and triplets have been recorded. At birth, a cub weighs only 1.3 pounds (about half a kilogram), but they grow very quickly. Cubs depend on their mothers for warmth and fattening milk, which is 36 percent fat, according to the San Diego Zoo. By spring, the cubs are outside the den, exploring, and at two years of age they are fully mature. Polar bears live around 15 to 20 years.

Polar Bear Classification and Taxonomy

> Kingdom: Animalia
> Subkingdom: Bilateria
> Infrakingdom: Deuterostomia
> Phylum: Chordata
> Subphylum: Vertebrata
> Infraphylum: Gnathostomata
> Superclass: Tetrapoda
> Class: Mammalia
> Infraclass: Eutheria
> Order: Carnivora
> Suborder: Caniformia
> Family: Ursidae
> Genus & species: Ursus maritimus

Polar Bear Facts

> Their fat not only keeps polar bears warm, it also increases their buoyancy when they swim.

> Polar bears have built-in socks. The bottoms of their paws are covered with fur to keep them warm and to help with traction in slippery situations.

> A polar bear can sniff out a seal’s breathing hole from more than half a mile away, according to the National Zoo. The bears can smell a seal on the ice 20 miles (32 kilometers) away.

> Polar bears succeed in catching their prey in only 2 percent of their attempts, the National Zoo says.

> The Inuit people still hunt polar bears for meat and fur, but hunting is carefully regulated by a quota system, according to Polar Bears International. Hunters pay respect to the bear’s soul (“tatkok”) by hanging the skin in an honored place in their igloo for several days. Inuit call polar bears “Nanuk” and believe they are wise, powerful and “almost a man.”

> The Sami (or Lapp) people refuse to say the polar bear’s name for fear of offending it. Instead, they call it “God’s dog” or “old man in the fur cloak,” according to Polar Bears International.

Polar Bear Documentaries

BBC The Polar Bear

National Geographic Documentary – Polar Bear

Life of Polar Bear Alcatraz – BBC documentary

World Of Discovery – Polar Bears

More Polar Bear Facts

1. The longest recorded nonstop swim a polar bear has ever made is 426 miles over nine days straight. Watch out Michael Phelps – that’s equivalent to the distance between Washington, D.C., and Boston. During the swim, the female bear lost 22 percent of her body weight. Studies have predicted more long-distance swims are in polar bears’ future due to the shrinking ice caps.

2. The Latin name for polar bears is “ursus maritimus,” which means sea bear. In Inuit mythology, the polar bear is called Pihoqahiak, the “ever-wandering one.”

3. Speaking of languages, the translations to the word(s) for “polar bear” are quite broad. Some of them include lord of the Arctic. Old man in the fur cloak.

4. Female polar bears typically give birth to twin cubs, which stay with her for more than two years until they can hunt and survive on their own. Females receive no help from their solitary male mates.

5. The average adult female weights about 570 pounds. However, when pregnant, they can reach weights as heavy as 1,100 pounds. A fully grown male weighs around 1,000 pounds.

6. The average lifepsan of the bear in the wild is 15 to 18 years.

7. These bears are one of the animals most affected by climate change, with the land literally melting beneath their paws.

8. Seals make up most of a polar bear’s diet.

9.They are the world’s largest land predator and biggest member of the bear family.

10. Their blubber gets up to four inches thick. Under their white fur – which is great camouflage – polar bears have black skin to better soak in the sun’s warmth. Fur even grows on the bottom of their claws, which protects against cold surfaces.

11. Although most polar bears are born on land, they spend most of their time at sea. Two of the Arctic’s most important habitats for them are the Beaufort and Chukchi seas.

12. Polar bears are the only type of bear considered a marine animal.

13. While polar bears look appealing, they are intense predators that rarely fear humans, which can make them dangerous.

14. These arctic kings have no natural enemies.

Polar Bear Pictures

Polar Bear Papers / PDF’s

> Behaviors of Polar Bears with Cub’s in Denning Areas.
> Reproductive Biology and Ecology of Female Polar Bears.
> Terrestrial Predation by Polar Bears.
> Polar Bear Fact Sheet.
> The Polar Bear – Biology Management and Conservation.
> Polar Bear – Effects of Climate Change on Polar Bears.
> General Information of Polar Bears.

– Credit and Resource –

LiveScience

Wiki

hurtigruten

In The Life of a Polar Bear

Tuesday, 3 February 2015

Worms Tasting light

Newly discovered taste receptors for hydrogen peroxide allow worms to indirectly detect light.

Human taste receptors are specialized to distinguish several distinct compounds: sugars taste sweet, salts taste salty, and acidic compounds taste sour. Now a new study from MIT finds that the worm Caenorhabditis elegans has taken its powers of detection a step further: The worm can taste hydrogen peroxide, triggering it to stop eating the potentially dangerous substance.

This image shows where the GUR-3 protein is expressed in the worm, which includes the I2 neurons.

Being able to taste hydrogen peroxide allows the worm to detect light, which generates hydrogen peroxide and other harmful reactive oxygen compounds both within the worm and in its environment.

“This is potentially a brand-new mechanism of sensing light,” says Nikhil Bhatla, the lead author of the paper and a postdoc in MIT’s Department of Biology. “All of the mechanisms of light detection we know about involve a chromophore — a small molecule that absorbs a photon and changes shape or transfers electrons. This seems to be the first example of behavioral light-sensing that requires the generation of a chemical in the process of detecting the light.”

Bhatla and Robert Horvitz, the David H. Koch Professor of Biology, describe the new hydrogen peroxide taste receptors in the Jan. 29 online issue of the journal Neuron. Though it is not yet known whether there is a human equivalent of this system, the researchers say their discovery lends support to the idea that there may be human taste receptors dedicated to flavors other than the five canonical ones — sweet, salty, bitter, sour, and savory. It also opens the possibility that humans might be able to sense light in ways that are fundamentally different from those known to act in vision.

“I think we have underestimated our biological abilities,” Bhatla says. “Aside from those five, there are other flavors, such as burnt. How do we taste something as burnt? Or what about spicy, or metallic, or smoky? There’s this whole new area that hasn’t really been explored.”

Beyond bitter and sweet

One of the major functions of the sense of taste is to determine whether something is safe, or advantageous, to eat. For humans and other animals, bitterness often serves as a warning of poison, while sweetness can help to identify foods that are rich in energy.

For worms, hydrogen peroxide can be harmful because it can cause extensive cellular trauma, including damaging proteins, DNA, and other molecules in the body. In fact, certain strains of bacteria produce hydrogen peroxide that can kill C. elegans after being eaten. Worms might also ingest hydrogen peroxide from the soil where they live.

Bhatla and Horvitz found that worms stop eating both when they taste hydrogen peroxide and when light shines on them — especially high-energy light, such as violet or ultraviolet. The authors found the exact same feeding response when worms were exposed to either hydrogen peroxide or light, which suggested to them that the same mechanism might be controlling responses to both stimuli.

Worms are known to be averse to light: Previous research by others has shown that they flee when light shines on them. Bhatla and Horvitz have now found that this escape response, like the feeding response to light, is likely caused by light’s generation of chemicals such as hydrogen peroxide.

The C. elegans worm has a very simple and thoroughly mapped nervous system consisting of 302 neurons, 20 of which are located in the pharynx, the feeding organ that ingests and grinds food. Bhatla found that one pair of pharyngeal neurons, known as the I2 neurons, controls the animal’s response to both light and hydrogen peroxide. A particular molecular receptor in that neuron, gustatory receptor 3 (GUR-3), and a molecularly similar receptor found in other neurons (LITE-1) are critical to the response. However, each receptor appears to function in a slightly different way.

GUR-3 detects hydrogen peroxide, whether it is found naturally in the environment or generated by light. There are many GUR-3 receptors in the I2 neuron, and through a mechanism that remains unknown, hydrogen peroxide stimulation of GUR-3 causes the pharynx to stop grinding. Another molecule called peroxiredoxin, an antioxidant, appears to help GUR-3 detect hydrogen peroxide.

While the GUR-3 receptor responds much more strongly to hydrogen peroxide than to light, the LITE-1 receptor is much more sensitive to light than to hydrogen peroxide. LITE-1 has previously been implicated in detecting light, but until now, it has been a mystery how a taste receptor could respond to light. The new study suggests that like GUR-3, LITE-1 indirectly senses light by detecting reactive oxygen compounds generated by light — including, but not limited to, hydrogen peroxide.

Kenneth Miller of the Oklahoma Medical Research Foundation published a paper in 2008 describing LITE-1 and hypothesizing that it might work by detecting a chemical product of light interaction. “This paper goes one step beyond that and identifies molecules that LITE-1 could be sensing to identify the presence of light,” says Miller, who was not part of the new study. “I thought it was a fascinating look at the complex gustatory sensory mechanism for molecules like hydrogen peroxide.”

Not found in humans

The molecular family of receptors that includes GUR-3 and LITE-1 is specific to invertebrates, and is not found in humans. However, peroxiredoxin is found in humans, particularly in the eye, so the researchers suspect that peroxiredoxin might play a role in detecting reactive oxygen species generated by light in the eye.

The researchers are now trying to figure out the exact mechanism of hydrogen peroxide detection: For example, how exactly do these gustatory receptors detect reactive oxygen compounds? The researchers are also working to identify the neural circuit diagram that defines how the I2 neurons interact with other neurons to control the worms’ feeding behavior. Such neural circuit diagrams should provide insight into how the brains of worms, and people, generate behavior.

The research was funded by the National Science Foundation, the National Institutes of Health, and the Howard Hughes Medical Institute.

– Credit and Resources –

Anne Trafton | MIT News Office

Worms Tasting light

NASA Europa Mission Gets White House Approval

The quest to explore Jupiter’s ocean-harboring moon Europa has taken a big step forward.

A new view of Europa based on information from NASA’s Galileo mission of the 1990s. This new, remastered version, released in 2014, features more realistic colors that resemble what the Jupiter moon would look like to the human eye. Credit: NASA/JPL-Caltech/SETI Institute

The White House’s fiscal year 2016 budget request for NASA, which was released Monday (Feb. 2), allocates $18.5 billion to the space agency, including $30 million to formulate a mission to Europa, perhaps the solar system’s best bet to host alien life. NASA has been studying a potential Europa mission for a while now, but the new budget proposal signals a commitment from the White House that wasn’t there before.

“For the first time, the budget supports the formulation and development of a Europa Mission, allowing NASA to begin project formulation, Phase A,” NASA officials wrote in a summary of the proposed budget.

[sorry may not work on some mobile devices :(]

Indeed, the new budget request assumes multiple years of funding for a Europa mission, said NASA Chief Financial Officer David Radzanowski.

“The current funding profile would assume a launch in the mid-2020s,” Radzanowski told reporters during a conference call Monday.

It’s unclear at the moment just how much NASA and the Europa project will actually get in the 2016 fiscal year (FY), which begins Oct. 1, 2015. Congress must approve the final budget, which often looks quite different than the one proposed by the White House.

For example, the Obama administration allocated $15 million for early work on a potential Europa mission in its FY 2015 budget request, but Congress later upped that to $100 million.

NASA appears to be zeroing in on a mission that would feature multiple flybys of Europa — perhaps something along the lines of the Europa Clipper, a concept being developed by agency scientists and engineers. Once in orbit around Jupiter, the Clipper would make 45 flybys of the 1,900-mile-wide (3,100 kilometers) Europa over the course of 3.5 years, as the concept is currently envisioned.

Europa is thought to possess an ocean of liquid water under its icy shell. During its many flybys, the Clipper would confirm and study that ocean, yielding insights about its depth, salinity and conductivity, among other characteristics.

The Clipper would also measure and map Europa’s ice shell, returning data that could be useful for a potential future mission to the moon’s surface.

“Sounding the ice shell would be key,” said David Senske of NASA’s Jet Propulsion Laboratory in Pasadena, California, Europa Clipper pre-project deputy project scientist.

“We have a preconceived notion of what a lander looks like,” Senske told Space.com in December at the annual fall meeting of the American Geophysical Union in San Francisco. “What we find may not support our preconceived notion.”

If everything goes according to plan, the Europa Clipper could be ready to launch as early as 2022, Senske said. The mission would probably cost about $2 billion.

The Europa mission will really start coming into focus just a few months from now: NASA aims to select science instruments for the mission this spring, NASA Administrator Charles Bolden said Monday. (The agency asked scientists around the world to propose instruments in July 2014.)

– Credit and Resource –

NASA

NASA Europa Mission Gets White House Approval

Parallelizing common algorithms

Researchers revamp a common “data structure” so that it will work with multicore chips.

Every undergraduate computer-science major takes a course on data structures, which describes different ways of organizing data in a computer’s memory. Every data structure has its own advantages: Some are good for fast retrieval, some for efficient search, some for quick insertions and deletions, and so on.

Today, hardware manufacturers are making computer chips faster by giving them more cores, or processing units. But while some data structures are well adapted to multicore computing, others are not. In principle, doubling the number of cores should double the efficiency of a computation. With algorithms that use a common data structure called a priority queue, that’s been true for up to about eight cores — but adding any more cores actually causes performance to plummet.

At the Association for Computing Machinery’s Symposium on Principles and Practice of Parallel Programming in February, researchers from MIT’s Computer Science and Artificial Intelligence Laboratory will describe a new way of implementing priority queues that lets them keep pace with the addition of new cores. In simulations, algorithms using their data structure continued to demonstrate performance improvement with the addition of new cores, up to a total of 80 cores.

A priority queue is a data structure that, as its name might suggest, sequences data items according to priorities assigned them when they’re stored. At any given time, only the item at the front of the queue — the highest-priority item — can be retrieved. Priority queues are central to the standard algorithms for finding the shortest path across a network and for simulating events, and they’ve been used for a host of other applications, from data compression to network scheduling.

With multicore systems, however, conflicts arise when multiple cores try to access the front of a priority queue at the same time. The problem is compounded by modern chips’ reliance on caches — high-speed memory banks where cores store local copies of frequently used data.

“As you’re reading the front of the queue, the whole front of the queue will be in your cache,” says Justin Kopinsky, an MIT graduate student in electrical engineering and computer science and one of the new paper’s co-authors. “All of these guys try to put the first element in their cache and then do a bunch of stuff with it, but then somebody writes to it, and it invalidates everybody else’s cache. And this is like an order-of-magnitude slowdown — maybe multiple orders of magnitude.”

Loosening up

To avoid this problem, Kopinsky; fellow graduate student Jerry Li; their advisor, professor of computer science and engineering Nir Shavit; and Microsoft Research’s Dan Alistarh, a former student of Shavit’s, relaxed the requirement that each core has to access the first item in the queue. If the items at the front of the queue can be processed in parallel — which must be the case for multicore computing to work, anyway — they can simply be assigned to cores at random.

But a core has to know where to find the data item it’s been assigned, which is harder than it sounds. Data structures generally trade ease of insertion and deletion for ease of addressability. You could, for instance, assign every position in a queue its own memory address: To find the fifth item, you would simply go to the fifth address.

But then, if you wanted to insert a new item between, say, items four and five, you’d have to copy the last item in the queue into the first empty address, then copy the second-to-last item into the address you just vacated, and so on, until you’d vacated address five. Priority queues are constantly being updated, so this approach is woefully impractical.

An alternative is to use what’s known as a linked list. Each element of a linked list consists of a data item and a “pointer” to the memory address of the next element. Inserting a new element between elements four and five is then just a matter of updating two pointers.

Road less traveled

The only way to find a particular item in a linked list, however, is to start with item one and follow the ensuing sequence of pointers. This is a problem if multiple cores are trying to modify data items simultaneously. Say that a core has been assigned element five. It goes to the head of the list and starts working its way down. But another core is already in the process of modifying element three, so the first core has to sit and wait until it’s done.

The MIT researchers break this type of logjam by repurposing yet another data structure, called a skip list. The skip list begins with a linked list and builds a hierarchy of linked lists on top of it. Only, say, half the elements in the root list are included in the list one layer up the hierarchy. Only half the elements in the second layer are included in the third, and so on.

The skip list was designed to make moving through a linked list more efficient. To find a given item in the root list, you follow the pointers through the top list until you identify the gap into which it falls, then move down one layer and repeat the process.

But the MIT researchers’ algorithm starts farther down the hierarchy; how far down depends on how many cores are trying to access the root list. Each core then moves some random number of steps and jumps down to the next layer of the hierarchy. It repeats the process until it reaches the root list. Collisions can still happen, particularly when a core is modifying a data item that appears at multiple levels of the hierarchy, but they become much rarer.

– Credit and Resource –

Larry Hardesty | MIT News Office

Parallelizing common algorithms

Qubits with staying power

Technique greatly extends duration of fragile quantum states, pointing toward practical quantum computers.

Quantum computers are experimental devices that promise exponential speedups on some computational problems. Where a bit in a classical computer can represent either a 0 or a 1, a quantum bit, or qubit, can represent 0 and 1 simultaneously, letting quantum computers explore multiple problem solutions in parallel. But such “superpositions” of quantum states are, in practice, difficult to maintain.

The researchers’ device is a ladderlike structure etched into diamond. The gaps between the ladder’s “rungs” act like a mirror, temporarily trapping light particles emitted at the ladder’s center.

In a paper appearing this week in Nature Communications, MIT researchers and colleagues at Brookhaven National Laboratory and the synthetic-diamond company Element Six describe a new design that in experiments extended the superposition time of a promising type of qubit a hundredfold.

In the long term, the work could lead toward practical quantum computers. But in the shorter term, it could enable the indefinite extension of quantum-secured communication links, a commercial application of quantum information technology that currently has a range of less than 100 miles.

The researchers’ qubit design employs nitrogen atoms embedded in synthetic diamond. When nitrogen atoms happen to be situated next to gaps in the diamond’s crystal lattice, they produce “nitrogen vacancies,” which enable researchers to optically control the magnetic orientation, or “spin,” of individual electrons and atomic nuclei. Spin can be up, down, or a superposition of the two.

To date, the most successful demonstrations of quantum computing have involved atoms trapped in magnetic fields. But “holding an atom in vacuum is difficult, so there’s been a big effort to try to trap them in solids,” says Dirk Englund, the Jamieson Career Development Assistant Professor in Electrical Engineering and Computer Science at MIT and corresponding author on the new paper. “In particular, you want a transparent solid, so you can send light in and out. Crystals are better than many other solids, like glass, in that their atoms are nice and regular and their electronic structure is well defined. And amongst all the crystals, diamond is a particularly good host for capturing an atom, because it turns out that the nuclei of diamond are mostly free of magnetic dipoles, which can cause noise on the electron spin.”

Light conversation

In bulk diamond, superpositions of the spins in nitrogen vacancies can last almost a second. But in order to communicate with each other, nitrogen-vacancy qubits need to be able to transfer information via particles of light, or photons. This requires positioning the vacancy inside an optical resonator, which temporarily traps photons.

Previously, devices consisting of nitrogen vacancies inside optical resonators exhibited a superposition time of only around a microsecond. The researchers’ new design gets that up to 200 microseconds.

For quantum computing applications, however, it’s not enough to keep individual qubits in superposition. Their quantum states also need to be “entangled,” so that if one qubit falls out of superposition — if it takes on a definite value of either 0 or 1 — it constrains the possible states of the other qubits.

In systems that use light to move information between nitrogen-vacancy qubits, entanglement occurs when light particles emitted by the qubits reach an optical component — such as a beam splitter — at the same time. With the earlier systems, it generally took several minutes to produce entanglement between qubits. With the new system, it should take milliseconds.

That’s still too long: A practical device would need to entangle photons before their corresponding qubits fell out of superposition, or “decohered.” “But the numbers actually look quite promising,” Englund says. “In the coming years, the entanglement rate could be orders of magnitude faster than the decoherence.”

The researchers’ device consists of a ladderlike diamond structure with a nitrogen vacancy at its center, which is suspended horizontally above a silicon substrate. Shining light perpendicularly onto the ladder kicks the electron in the nitrogen vacancy into a higher-energy state. When it drops back down to its ground state, it releases that excess energy as a photon, whose quantum states can be correlated with its own.

The gaps in the diamond structure — the spaces between rungs in the ladder — act as what’s called a photonic crystal, confining the photon so that it bounces back and forth across the vacancy thousands of times. When the photon finally emerges, it has a high likelihood of traveling along the axis of the ladder, so that it can be guided into an optical fiber.

The right direction

Practically, the only way to synchronize the photons emitted by different qubits is probabilistically: Repeat the experiment enough, and eventually the photons will arrive at the optical component at the same time. In previous systems, both the time and the direction of the photons’ emission were left to chance. In the new system, the timing is still erratic, but direction is much more reliable. That, together with the greater purity of the emitted light, should reduce the time required to produce entanglement.

The researchers’ manufacturing process begins with a 5-micrometer-thick wafer of synthetic diamond with nitrogen atoms embedded in it at regular intervals, which is , made by Element Six. The MIT researchers use an oxygen plasma to reduce the diamond’s thickness to only 200 nanometers.

The resulting fragments of diamond are too small to etch using standard lithographic processes. So the MIT researchers developed a new technique in which they affix silicon membranes etched into ladder patterns to the diamond, then again use an oxygen plasma to remove the material not shielded by the silicon. They transfer the resulting structures to a chip using a tungsten atomic probe with a slightly sticky drop of silicone at its tip.

“Etching via a hard mask rather than a focused-ion beam seems to have kept the diamond material free of defects, thus sustaining the spin coherence,” says Mete Atature, a reader in physics at the University of Cambridge who was not involved in the research. “This is an important step toward the utilization of nitrogen-vacancy centers as efficient sources of entanglement, quantum repeaters, or quantum memories within a distributed network. The higher collection efficiency will lead to both faster generation and faster verification of entanglement, so it is analogous to being able to increase the clock rate of a computing device.”

– Credit and Resources –

Larry Hardesty | MIT News Office

Qubits with staying power

Cassini Catches Titan Naked in the Solar Wind

Researchers studying data from NASA’s Cassini mission have observed that Saturn’s largest moon, Titan, behaves much like Venus, Mars or a comet when exposed to the raw power of the solar wind. The observations suggest that unmagnetized bodies like Titan might interact with the solar wind in the same basic ways, regardless of their nature or distance from the sun.

This diagram depicts conditions observed by NASA’s Cassini spacecraft during a flyby in Dec. 2013, when Saturn’s magnetosphere was highly compressed, exposing Titan to the full force of the solar wind.
Image Credit:
NASA/JPL-Caltech

Titan is large enough that it could be considered a planet if it orbited the sun on its own, and a flyby of the giant moon in Dec. 2013 simulated that scenario, from Cassini’s vantage point. The encounter was unique within Cassini’s mission, as it was the only time the spacecraft has observed Titan in a pristine state, outside the region of space dominated by Saturn’s magnetic field, called its magnetosphere.

“We observed that Titan interacts with the solar wind very much like Mars, if you moved it to the distance of Saturn,” said Cesar Bertucci of the Institute of Astronomy and Space Physics in Buenos Aires, who led the research with colleagues from the Cassini mission. “We thought Titan in this state would look different. We certainly were surprised,” he said.

The solar wind is a fast-flowing gale of charged particles that continually streams outward from the sun, flowing around the planets like islands in a river. Studying the effects of the solar wind at other planets helps scientists understand how the sun’s activity affects their atmospheres. These effects can include modification of an atmosphere’s chemistry as well as its gradual loss to space.

Titan spends about 95 percent of the time within Saturn’s magnetosphere. But during a Cassini flyby on Dec. 1, 2013, the giant moon happened to be on the sunward side of Saturn when a powerful outburst of solar activity reached the planet. The strong surge in the solar wind so compressed the sun-facing side of Saturn’s magnetosphere that the bubble’s outer edge was pushed inside the orbit of Titan. This left the moon exposed to, and unprotected from, the raging stream of energetic solar particles.

Using its magnetometer instrument, which is akin to an equisitely sensitive compass, Cassini has observed Titan many times during the mission’s decade in the Saturn system, but always within Saturn’s magnetosphere. The spacecraft has not been able to detect a magnetic field coming from Titan itself. In its usual state, Titan is cloaked in Saturn’s magnetic field.

This time the influence of Saturn was not present, allowing Cassini’s magnetometer to observe Titan as it interacted directly with the solar wind. The special circumstance allowed Bertucci and colleagues to study the shockwave that formed around Titan where the full-force solar wind rammed into the moon’s atmosphere.

At Earth, our planet’s powerful magnetic field acts as a shield against the solar wind, helping to protect our atmosphere from being stripped away. In the case of Venus, Mars and comets — none of which is protected by a global magnetic field — the solar wind drapes around the objects themselves, interacting directly with their atmospheres (or in the comet’s case, its coma). Cassini saw the same thing at Titan.

Researchers thought they would have to treat Titan’s response to the solar wind with a unique approach because the chemistry of the hazy moon’s dense atmosphere is highly complex. But Cassini’s observations of a naked Titan hinted at a more elegant solution. “This could mean we can use the same tools to study how vastly different worlds, in different parts of the solar system, interact with the wind from the sun,” Bertucci said.

Bertucci noted that the list of similarly unmagnetized bodies might include the dwarf planet Pluto, to be visited this year for the first time by NASA’s New Horizons spacecraft.

“After nearly a decade in orbit, the Cassini mission has revealed once again that the Saturn system is full of surprises,” said Michele Dougherty, principal investigator of the Cassini magnetometer at Imperial College, London. “After more than a hundred flybys, we have finally encountered Titan out in the solar wind, which will allow us to better understand how such moons maintain or lose their atmospheres.”

The new research is published today in the journal Geophysical Research Letters.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The magnetometer team is based at Imperial College, London, U.K.

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NASA

Cassini Catches Titan Naked in the Solar Wind