How bird flocks are like liquid helium | Science/AAAS | News

How bird flocks are like liquid helium | Science/AAAS | News: Using tracking software on the recorded video, the team could pinpoint when and where individuals decide to turn, information that enabled them to follow how the decision sweeps through the flock. The tracking data showed that the message to turn started from a handful of birds and swept through the flock at a constant speed between 20 and 40 meters per second. That means that for a group of 400 birds, it takes just a little more than a half-second for the whole flock to turn...

The team proposes that instead of copying the direction in which a neighbor flies, a bird copies how sharply a neighbor turns...

Interestingly, Cavagna adds, the new model is mathematically identical to the equations that describe superfluid helium.

A black hole in a bath: Big physics on a bench-top - physics-math - 10 March 2014 - New Scientist

A black hole in a bath: Big physics on a bench-top - physics-math - 10 March 2014 - New Scientist

Supersymmetry...  One of its central predictions is that there should be more than one Higgs particle... they might have found some clue as to where those extra particles might be – in superfluid helium-3... The discovered Higgs weighs in at around 125 gigaelectronvolts (GeV). Studying the spectrum of excitations in the superfluid helium suggests Higgs particles should also exist at energies of 210 GeV and 325 GeV. These possibilities are not excluded by results collected so far at the LHC...

By concentrating laser light into a very small spot within a waveguide made of a glass block, he can temporarily change the refractive index of the glass so that it slows down subsequent laser pulses and ultimately repels them. "What makes these analogue experiments so powerful is that from a photon or a water wave's perspective, it has no way of distinguishing whether it is crossing the event horizon of a real black hole or is in a waveguide under some weird constraints," he says.

Speed limit on a superfluid helium nano-highway

Speed limit on a superfluid helium nano-highway: The new research has now shown that even in tiny nanodroplets, helium still exhibits superfluidity...


The result of the experiment was quite astonishing: the measured velocity is always the same. It does not matter whether the impurity is a metal atom, a diatomic molecule or a polyatomic molecule with a cage structure: they all leave the droplet with the same speed. Mass or size thus does not matter. Even the repulsive force (which could be tuned with the laser pulse) turned out not to be of any influence.

Two-laser boron fusion lights the way to radiation-free energy : Nature News & Comment

Two-laser boron fusion lights the way to radiation-free energy : Nature News: One laser created a short-lived plasma, or highly ionized gas of boron nuclei, by heating boron atoms; the other laser generated a beam of protons that smashed into the boron nuclei, releasing slow-moving helium particles but no neutrons...

The boron plasma generated by the laser lasts only about one-billionth of a second, and so the pulse of protons, which lasts one-trillionth of a second, must be precisely synchronized to slam into the boron target. The proton beam is preceded by a beam of electrons, generated by the same laser, that pushes away electrons in the boron plasma, allowing the protons more of a chance to collide with the boron nuclei and initiate fusion.

Ultimate chill: The epic race to reach absolute zero

Ultimate chill: The epic race to reach absolute zero
http://www.newscientist.com/article/mg21829222.100-ultimate-chill-the-epic-race-to-reach-absolute-zero.html?cmpid=RSS%7CNSNS%7C2012-GLOBAL%7Conline-news&utm_source=feedly


We can also use the incomparably pure quantum-dominated environments of ultra-cold materials to model extreme conditions in the interior of a neutron star, fundamental particle interactions, and phase transitions in the earliest moments of the universe. At low temperatures, electrons interact to create fundamental excitations – sometimes called quasiparticles – with a mass up to a thousand times that of a free electron, much as fundamental particles in free space acquire mass by interaction with the Higgs field. Similarly, quasiparticle excitations in superconductors have recently been shown to behave like Majorana particles, long-predicted objects that are their own antiparticles.

Superfluids: Observation of 'second sound' in a quantum gas

Superfluids: Observation of 'second sound' in a quantum gas: ...fluids in this state conduct heat extremely efficiently, with energy transport occurring in a distinct temperature wave. Because of the similarities to a sound wave, this temperature wave is also called second sound...


In the laboratory, Grimm's team of quantum physicists prepared a quantum gas consisting of about 300,000 lithium atoms. They heated the cigar-shaped particle cloud locally with a power-modulated laser beam and then observed the propagating temperature wave. "While in superfluid helium only one entropy wave is generated, our Fermi gas also exhibited some thermal expansion and, thus, a measurable density wave," explains Grimm the crucial difference.

A spiral through frozen helium

A spiral through frozen helium:

This spiral is a crystal of silicon carbide, made during an experiment conducted in 2007...

There are flaws in the crystal, and, when the mixture reached a certain temperature and pressure, the solid helium turned to a superfluid.

...The crystal of frozen helium was twisted around, and suddenly the twisting got easier, as if some of the mass had disappeared.

Existential blow for ghostly quantum supersolids - New Scientist - New Scientist

Existential blow for ghostly quantum supersolids - New Scientist: ...they sealed the glass with a thin layer of epoxy resin and inserted the helium through a very thin tube. This meant only a tiny fraction of the helium could become a bulk solid – and so any speeding up due to quantum plasticity would be negligible.

Chan and Duk Kim found that this set-up completely eliminated the changes in oscillation rate that they had originally observed. "We didn't see anything at all," says Chan. That suggests that all of the speeding up in the original experiment must have been due to bulk helium forming a quantum plastic, not supersolidity as originally claimed in 2004.

Flying object propels itself by flipping inside out

Flying object propels itself by flipping inside out: The design is based on the inverted cube shape discovered by inventor and mathematician Paul Schatz. By dissecting a cube into three parts, two star-shaped units can be produced at either end with an invertible belt in the middle section which is the same shape as the flying band. The system reproduces the entire structure: it opens to release the band while the ends remain on the ground as a docking station.

The flying object itself is made up of six identical prisms filled with helium, held together by a carbon-fibre framework. Three motors drive the motion coordinated by a tiny onboard computer, pre-programmed to replicate the inversion sequence...

Why Helium was the Dark Matter of its Day

Why Helium was the Dark Matter of its Day: In the middle of the 1800s, scientists couldn't stop puzzling over the strange data that they kept finding. When they looked at the sun and at other stars through spectroscopes, they found a funny line, a frequency of light that was emitting by something, but not by any element that they had gotten their hands on yet. This was not a negligible trace of plasma or whiff of gas. This was a full twenty-four percent of the mass of stars in the galaxy. Because it seemed a solely stellar element, in 1868 it was named 'helium,' after Helios, the sun god. It was clearly a massive chunk of the universe of which we were a part, but no one could get their hands on it.

Superstuff: When quantum goes big

Superstuff: When quantum goes big: Imagine you have two identical particles, and you swap their positions. The physical system looks exactly the same, and responds to an experiment exactly as before. However, quantum theory records the swap by multiplying their quantum state by a "phase factor". Switching the particles again brings in the phase factor a second time, but the particles are in their original position and so everything returns to its original state. "Since switching the particles twice brings you back to where you were, multiplying by this phase twice must do nothing at all," says John Baez at the Centre for Quantum Technologies in Singapore. This means that squaring the phase must give 1, which in turn means that the phase itself can be equal to 1 or -1.

Single molecule can shift the phase of a laser beam

Single molecule can shift the phase of a laser beam: To demonstrate how a molecule can change the phase of a light beam, the researchers detected organic molecules (dibenzanthanthrene) embedded in a solid matrix by performing coherent extinction spectroscopy at liquid helium temperature (near absolute zero). In this procedure, they tightly focused an excitation laser beam on the molecular sample in front of a mirror.
Next, the researchers arranged an interferometer consisting of two laser beams traveling the same path but with a small (115 MHz) frequency offset. As the laser frequencies traveled through the resonance of a single molecule, the researchers observed that the phase of one of the two interferometer beams was shifted by three degrees.

Physicists hit on mathematical description of superfluid dynamics

Physicists hit on mathematical description of superfluid dynamics: As a neutron star rotates, the superfluid on the surface behaves quite differently than a liquid would on the surface of the Earth. As the rotational speed increases the fluid opens a series of small vortices. As the vortices assemble into triangular patterns, the triangles build a lattice structure within the superfluid.
"When you reach the correct speed, you'll create one vortex in the middle," Bulgac said. "And as you increase the speed, you will increase the number of vortices. But it always occurs in steps."

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics: In fact, in this paper, the researchers show instead a more prosaic explanation: There are moving defects in the solid helium crystals, and their relaxation time falls with rising temperatures. This is more consistent with the torsional oscillation (shaking) experiments conducted at Cornell.
The researchers learned that the unusual properties of solid helium do not reflect a clunky transition between the solid state and a supersolid state. It behaves like a dimmer switch and presents a smooth transition near absolute zero.

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics: In fact, in this paper, the researchers show instead a more prosaic explanation: There are moving defects in the solid helium crystals, and their relaxation time falls with rising temperatures. This is more consistent with the torsional oscillation (shaking) experiments conducted at Cornell.
The researchers learned that the unusual properties of solid helium do not reflect a clunky transition between the solid state and a supersolid state. It behaves like a dimmer switch and presents a smooth transition near absolute zero.

Moved By Light - Science News

Moved By Light - Science News: While other scientists built stuff that shook thousands or millions of times a second, he created a ceramic wafer 30 micro-meters long that expanded and contracted 6 billion times per second. The faster an object’s natural quiver, the easier it is to remove energy, meaning less cooling needed to reach the ground state. Using a state-of-the-art liquid-helium refrigerator capable of achieving millikelvin temperatures, Cleland’s team put the wafer in its ground state 93 percent of the time.

By measuring the electric fields produced by this object, Cleland and his colleagues showed that they could nudge the wafer into a state of superposition — both moving and still at the same time.

Scientists make quantum breakthrough

Scientists make quantum breakthrough: “In an optical fibre, many modes of light can be conducted simultaneously, and they can interfere to produce a speckled pattern of light...
“We have shown that when atoms in a vacuum chamber are guided inside a laser light beam, they too can create a speckle pattern - an image of which we have captured for the first time”.
The team trapped a cloud of cold helium atoms at the focus of an intense laser beam pointed downwards at the imaging system, and then gradually turned down the laser intensity until the speckled image appeared.
“We then made the atoms even colder,” says team leader Dr Andrew Truscott, “until they behaved more like waves than particles, forming a single quantum wave called a Bose-Einstein condensate (BEC).  When the BEC was loaded into the guide, the speckle pattern disappeared, showing that just one mode was being transmitted – the single quantum wave.”

Superconductivity's Smorgasbord of Insights: A Movable Feast

Superconductivity's Smorgasbord of Insights: A Movable Feast: Physicists have applied the theory of superconductivity directly to nuclear matter, liquid helium, and ultracold atomic gases. Historically, insights from superconductivity convinced theorists of the importance of symmetries and the ways in which a physical system can muddle or “break” them. The concept of “spontaneous symmetry breaking” now undergirds theory in many fields, especially particle physics. “It was not a way that people were thinking, certainly not in elementary particle physics,” says Gordon Baym, a theorist at the University of Illinois, Urbana-Champaign. Superconductivity, he says, “changed the way people thought in different fields..."


The BCS model was more than a one-trick pony. Bardeen, Cooper, and Schrieffer had based it on just two assumptions: that the particles are fermions and that they attract each other. So “it was obvious to all of us” that the theory would apply to other particles interacting through different forces, Cooper says.
First came applications to atomic nuclei. In the summer of 1957, before the BCS theory was published, Pines visited the University of Copenhagen. There he, Aage Bohr (Niels Bohr's son), and Ben Mottelson found they could explain long-standing puzzles, such as why nuclei with an even number of protons and even number of neutrons are particularly tightly bound. The protons and neutrons, also fermions, independently pair.

First Observation of Antihelium� - Technology Review

First Observation of Antihelium� - Technology Review: What's important about this observation is that antihelium-4 seems to occur at exactly the rate predicted by thermodynamics. So unless there's some other mechanism for making it in vastly greater quantities, we're unlikely to see a naturally occurring version, no matter how hard we look.

So "any observation of antihelium or even heavier antinuclei in space would indicate the existence of a large amount of antimatter elsewhere in the Universe," say the STAR collaboration.

Quantum Whirls - Science News

Quantum Whirls - Science News: ...His experiments involved spinning a cylinder the size of a skateboard and watching how the liquid helium sloshed inside.
Frustrated that none of the tracer particles he could buy would float, he created a new technique to freeze hydrogen, the only element lighter than helium, into a fog of ice particles. He sprinkled the hydrogen particles like snow onto the helium. They floated...
...Bewley shined a laser onto the supercold liquid with the hydrogen snow. He was shocked to see Feynman’s vortices pop into existence and bump into each other. A few days later, he and his adviser caught the whole dance on tape...
...The way that vortices snapped away from each other is similar to how Drake imagined magnetic field lines twisting in the sun...