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Virtual quantum particles can have real physical effects: A vacuum can yield flashes of light

Virtual quantum particles can have real physical effects: A vacuum can yield flashes of light | Science Communication from mdashf | Scoop.it

A vacuum might seem like empty space, but scientists have discovered a new way to seemingly get something from that nothingness, such as light. And the finding could ultimately help scientists build incredibly powerful quantum computers or shed light on the earliest moments in the universe's history.

 

Quantum physics explains that there are limits to how precisely one can know the properties of the most basic units of matter—for instance, one can never absolutely know a particle's position and momentum at the same time. One bizarre consequence of this uncertainty is that a vacuum is never completely empty, but instead buzzes with so-called “virtual particles” that constantly wink into and out of existence.

 

These virtual particles often appear in pairs that near-instantaneously cancel themselves out. Still, before they vanish, they can have very real effects on their surroundings. For instance, photons—packets of light—can pop in and out of a vacuum. When two mirrors are placed facing each other in a vacuum, more virtual photons can exist around the outside of the mirrors than between them, generating a seemingly mysterious force that pushes the mirrors together.

 

This phenomenon, predicted in 1948 by the Dutch physicist Hendrick Casimir and known as the Casimir effect, was first seen with mirrors held still . Researchers also predicted a dynamical Casimir effect that can result when mirrors are moved, or objects otherwise undergo change. Now quantum physicist Pasi Lähteenmäki at Aalto University in Finland and his colleagues reveal that by varying the speed at which light can travel, they can make light appear from nothing.

 

The speed of light in a vacuum is constant, according to Einstein's theory of relativity, but its speed passing through any given material depends on a property of that substance known as its index of refraction. By varying a material's index of refraction, researchers can influence the speed at which both real and virtual photons travel within it. Lähteenmäki says one can think of this system as being much like a mirror, and if its thickness changes fast enough, virtual photons reflecting off it can receive enough energy from the bounce to turn into real photons. "Imagine you stay in a very dark room and suddenly the index of refraction of light [of the room] changes," Lähteenmäki says. "The room will start to glow."

 

The researchers began with an array of 250 superconducting quantum-interference devices, or SQUIDs—circuits that are extraordinarily sensitive to magnetic fields. They inserted the array inside a refrigerator. By carefully exerting magnetic fields on this array, they could vary the speed at which microwave photons traveled through it by a few percent. The researchers then cooled this array to 50 thousandths of a degree Celsius above absolute zero. Because this environment is supercold, it should not emit any radiation, essentially behaving as a vacuum. "We were simply studying these circuits for the purpose of developing an amplifier, which we did," says researcher Sorin Paraoanu, a theoretical physicist at Aalto University. "But then we asked ourselves—what if there is no signal to amplify? What happens if the vacuum is the signal?"

 

The investigators caution that such experiments do not constitute a magical way to get more energy out of a system than what is input. For instance, it takes energy to change a material's index of refraction.

Instead, such research could help scientists learn more about the mysteries of quantum entanglement, which lies at the heart of quantum computers—advanced machines that could in principle run more calculations in an instant than there are atoms in the universe. The entangled microwave photons the experimental array generated "can be used for a form of quantum computation known as 'continuous variable' quantum information processing,” Girvin says. “This is a direction which is just beginning to open up.” Wilson adds that these systems “might be used to simulate some interesting scenarios. For instance, there are predictions that during cosmic inflation in the early universe, the boundaries of the universe were expanding nearly at light-speed or faster than the speed of light. We might predict there'd be some dynamical Casimir radiation produced then, and we can try and do tabletop simulations of this."

So the static Casimir effect involves mirrors held still; the dynamical Casimir effect can for instance involve mirrors that move.

 


Via Dr. Stefan Gruenwald
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Biomolecular Movie-Making with Atomic Force Microscopy

Biomolecular Movie-Making with Atomic Force Microscopy | Science Communication from mdashf | Scoop.it

Toshio Ando and co-workers at Kanazawa University have developed and used high-speed atomic force microscopy (HS-AFM) to achieve direct visualization of dynamic structural changes and processes of functioning biological molecules in physiological solution — creating microscopic movies of unprecedented sub-100-ms temporal resolution and submolecular spatial resolution.

 

To produce an image, HS-AFM acquires information on sample height at many points by tapping the sample with the sharp tip of a tiny cantilever and dragging the sharp tip of a tiny cantilever across the sample. Depending on the application, this might involve recording the distance of deflection, the amplitude and phase of oscillations, or the resonant frequency of the cantilever.

 

Ando and co-workers use very small cantilevers that provide 10 to 20 times the sensitivity of larger, conventional cantilevers. Copies of their home-made apparatus are now commercially available through the manufacturer Research Institute of Biomolecule Metrology Co., Ltd in Tsukuba, and record images at least ten times more quickly than their competitors.


Via Dr. Stefan Gruenwald
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Earth tide measurements provide the 'speed of gravity' which turns out identical to speed of light

Earth tide measurements provide the 'speed of gravity' which turns out identical to speed of light | Science Communication from mdashf | Scoop.it

Based on the Newtonian formula for the gravity of Earth's tides, a Chinese research team has found that gravity travels at the speed of light. After correcting out  the phase lag due to the anelasticity of the Earth, they found that the speed of gravity is between 0.93 to 1.05 times the speed of light with a relative error of about 5%. This provides first set of strong evidences to show that the speed of gravity is the same as the speed of light.


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Quantum Stealth Invisibility Cloak Gets Pentagon Backing

Quantum Stealth Invisibility Cloak Gets Pentagon Backing | Science Communication from mdashf | Scoop.it

The United States military is reportedly backing a Canadian company's development of a material that can render soldiers invisible, according to news reports. Maple Ridge, B.C.-based Hyperstealth Biotechnology has developed "Quantum Stealth," a type of camouflage that bends light around the wearer or an object to create the illusion of invisibility. President and CEO Guy Cramer likened the new technology to Harry Potter's invisibility cloak during a recent CNN appearance, and described its ability to easily and effectively hide a soldier in different environments.

 

"Unless you walked right into them, you wouldn't know that they were there," Cramer said. The material doesn't require batteries, projectors or cameras. It is also inexpensive and lightweight, according to Hyperstealth's website.

For security reasons, the company will not provide public demonstrations, only mockup photos. But Canadian military groups and the U.S. Federal Emergency Response Team have seen the technology and can back up his claims. Cramer described the material's incredible value to soldiers who carry out operations during the day, or those who are trying to evade their enemy, the Daily Mail reported. Beyond that, the technology could have use on a larger scale, on submarines, tanks or aircrafts.

 


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Einstein Was Right: Space-Time Is Smooth And Not Foamy

Einstein Was Right: Space-Time Is Smooth And Not Foamy | Science Communication from mdashf | Scoop.it
A new study supports Einstein's view over that of some quantum theorists.

 

A team of researchers came to this conclusion after tracing the long journey three photons took through intergalactic space. The photons were blasted out by an intense explosion known as a gamma-ray burst about 7 billion light-years from Earth. They finally barreled into the detectors of NASA's Fermi Gamma-ray Space Telescope in May 2009, arriving just a millisecond apart.

Their dead-heat finish strongly supports the Einsteinian view of space-time, researchers said. The wavelengths of gamma-ray burst photons are so small that they should be able to interact with the even tinier "bubbles" in the quantum theorists' proposed space-time foam.

 

If this foam indeed exists, the three protons should have been knocked around a bit during their epic voyage. In such a scenario, the chances of all three reaching the Fermi telescope at virtually the same time are very low, researchers said.

 

So the new study is a strike against the foam's existence as currently imagined, though not a death blow. "If foaminess exists at all, we think it must be at a scale far smaller than the Planck length, indicating that other physics might be involved," study leader Robert Nemiroff, of Michigan Technological University, said in a statement. The Planck length is an almost inconceivably short distance, about one trillionth of a trillionth the diameter of a hydrogen atom. 

 

"There is a possibility of a statistical fluke, or that space-time foam interacts with light differently than we imagined," added Nemiroff, who presented the results Wednesday (Jan. 9) at the 221st meeting of the American Astronomical Society in Long Beach, Calif.


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Quantum gas goes below absolute zero: Ultracold atoms pave way for negative-Kelvin materials

Quantum gas goes below absolute zero: Ultracold atoms pave way for negative-Kelvin materials | Science Communication from mdashf | Scoop.it

It may sound less likely than hell freezing over, but physicists have created an atomic gas with a sub-absolute-zero temperature for the first time. Their technique opens the door to generating negative-Kelvin materials and new quantum devices, and it could even help to solve a cosmological mystery.

 

Lord Kelvin defined the absolute temperature scale in the mid-1800s in such a way that nothing could be colder than absolute zero. Physicists later realized that the absolute temperature of a gas is related to the average energy of its particles. Absolute zero corresponds to the theoretical state in which particles have no energy at all, and higher temperatures correspond to higher average energies.

 

However, by the 1950s, physicists working with more exotic systems began to realize that this isn't always true: Technically, you read off the temperature of a system from a graph that plots the probabilities of its particles being found with certain energies. Normally, most particles have average or near-average energies, with only a few particles zipping around at higher energies. In theory, if the situation is reversed, with more particles having higher, rather than lower, energies, the plot would flip over and the sign of the temperature would change from a positive to a negative absolute temperature, explains Ulrich Schneider, a physicist at the Ludwig Maximilian University in Munich, Germany.

 

Schneider and his colleagues reached such sub-absolute-zero temperatures with an ultracold quantum gas made up of potassium atoms. Using lasers and magnetic fields, they kept the individual atoms in a lattice arrangement. At positive temperatures, the atoms repel, making the configuration stable. The team then quickly adjusted the magnetic fields, causing the atoms to attract rather than repel each other. “This suddenly shifts the atoms from their most stable, lowest-energy state to the highest possible energy state, before they can react,” says Schneider. “It’s like walking through a valley, then instantly finding yourself on the mountain peak.”

 

At positive temperatures, such a reversal would be unstable and the atoms would collapse inwards. But the team also adjusted the trapping laser field to make it more energetically favourable for the atoms to stick in their positions. This result, described today in Science, marks the gas’s transition from just above absolute zero to a few billionths of a Kelvin below absolute zero. Wolfgang Ketterle, a physicist and Nobel laureate at the Massachusetts Institute of Technology in Cambridge, who has previously demonstrated negative absolute temperatures in a magnetic system, calls the latest work an “experimental tour de force”. Exotic high-energy states that are hard to generate in the laboratory at positive temperatures become stable at negative absolute temperatures — “as though you can stand a pyramid on its head and not worry about it toppling over,” he notes — and so such techniques can allow these states to be studied in detail. “This may be a way to create new forms of matter in the laboratory,” Ketterle adds.


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MIT discovers a new state of matter, a new kind of magnetism

MIT discovers a new state of matter, a new kind of magnetism | Science Communication from mdashf | Scoop.it
Researchers at MIT have discovered a new state of matter with a new kind of magnetism. This new state, called a quantum spin liquid (QSL), could lead to significant advances in data storage.

 

Researchers at MIT have discovered a new state of matter with a new kind of magnetism. This new state, called a quantum spin liquid (QSL), could lead to significant advances in data storage. QSLs also exhibit a quantum phenomenon called long-range entanglement, which could lead to new types of communications systems, and more.

 

Generally, when we talk about magnetism’s role in the realm of technology, there are just two types: Ferromagnetism and antiferromagnetism. Ferromagnetism has been known about for centuries, and is the underlying force behind your compass’s spinning needle or the permanent bar magnets you played with at school. In ferromagnets, the spin (i.e. charge) of every electron is aligned in the same direction, causing two distinct poles. In antiferromagnets, neighboring electrons point in the opposite direction, causing the object to have zero net magnetism (pictured below). In combination with ferromagnets, antiferromagnets are used to create spin valves: the magnetic sensors used in hard drive heads.

 

In the case of quantum spin liquids, the material is a solid crystal — but the internal magnetic state is constantly in flux. The magnetic orientations of the electrons (their magnetic moment) fluctuate as they interact with other nearby electrons. “But there is a strong interaction between them, and due to quantum effects, they don’t lock in place,” says Young Lee, senior author of the research. It is these strong interactions that apparently allow for long-range quantum entanglement.


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