Quantum split: Particle this way, properties that way - physics-math - 23 July 2014 - New Scientist

Quantum split: Particle this way, properties that way - physics-math - 23 July 2014 - New Scientist: In Grenoble, the Vienna team used a feeble magnetic field and a weakly interacting neutron absorber to make the weak measurements. They found that when they put the absorber in one path of the interferometer (say left), there was a discernible effect at the output. But when they put it in the right path, it had no such effect. The neutrons were travelling in one path only.

Next, the experimenters introduced a weak magnetic field near each arm of the interferometer, to interact with the spin of the neutrons. When they did this in the left path, there was no change in the interferometer's output. If they introduced the magnetic field in the right path, though, there was a change: the magnetic field had interacted with the spin. In other words, they had confirmed that the spin had chosen the path not taken by the parent neutron...

New evidence to aid search for charge 'stripes' in superconductors

New evidence to aid search for charge 'stripes' in superconductors: ...uncovering the detailed relationship between these stripe patterns and the appearance or disappearance of superconductivity is extremely difficult, particularly because the stripes that may accompany superconductivity are very likely moving, or fluctuating.


The scientists ground up crystals of the test material into a fine powder and placed samples of it in line with a beam of neutrons...


With increasing temperature, the scientists found that while the aspect ratio of the crystal structure changed, the displacements from average structure persisted, leading them to conclude by inference that the striped pattern of charge density also remained, even though it was no longer static.

"This is the first powder diffraction scattering evidence for fluctuating charge stripes above the temperature where we see static order..."

Super-accurate atomic clock doubles up as quantum sim - physics-math - 08 August 2013 - New Scientist

Super-accurate atomic clock doubles up as quantum sim - physics-math - 08 August 2013 - New Scientist: Electrons' behaviour inside solids can be physically modelled using networks of atoms cooled to trillionths of a degree above absolute zero...

...she and her colleagues have stumbled upon a way to mimic quantum behaviour in a system several orders of magnitude warmer: an atomic clock...

Rey says that the strontium atoms in the ground state can be used to simulate spin-down electrons, and the excited atoms, spin-up electrons. Tracking the emergence and details of the interactions between the atoms could then shed light on the nature of the quantum interactions between electrons in magnets.

Quantum communication controlled by resonance in 'artificial atoms'

Quantum communication controlled by resonance in 'artificial atoms': "We capture the electrons in 'boxes'. Each box consist of a quantum dot, which is an artificial atom. The quantum dots are embedded in the semiconductor and each quantum dot can capture one electron. There needs to be three quantum dots next to each other using nanometer-scale electrostatic metal gates. When we open contact between the 'boxes' the electrons can sense each others' presence. The three spins must coordinate their orientations because it cost extra energy to put electrons with the same spin into the same box. To lower their energy, they not only spread out among the three boxes, but they orient their spins to further lower their energy. The three boxes together form a single entity – a qubit or quantum bit," explains Marcus.

An electrical signal is now sent from outside and by rapidly opening the boxes the system begins to swing in dynamic vibrations. The researchers can use this to change the quantum state of the electrons. "By combining three electrons in a triple quantum dot and oscillating an applied electric field at the frequency that separates adjacent energy levels, we can thus control the spins of the electrons without measuring them," explains Charles Marcus.

Physicists freeze motion of light for a minute

Physicists freeze motion of light for a minute: To stop the light, the physicists used a glass-like crystal that contains a low concentration of ions – electrically charged atoms – of the element praseodymium. The experimental setup also includes two laser beams. One is part of the deceleration unit, while the other is to be stopped. The first light beam, called the "control beam", changes the optical properties of the crystal: the ions then change the speed of light to a high degree. The second beam, the one to be stopped, now comes into contact with this new medium of crystal and laser light and is slowed down within it. When the physicists switch off the control beam at the same moment that the other beam is within the crystal, the decelerated beam comes to a stop.


More precisely, the light turns into a kind of wave trapped in the crystal lattice. This can be explained in greatly simplified form as follows. The praseodymium ions are orbited by electrons. These behave similarly to a chain of magnets: if you put one into motion, the movement – mediated by magnetic forces – propagates in the chain like a wave. Since physicists call the magnetism of electrons "spin", a "spin wave" forms in the same manner when freezing the laser beam. This is a reflection of the laser's light wave. In this way, the Darmstadt researchers were able to store images, such as a striped pattern, made of laser light within the crystal. The information can be read out again by turning the control laser beam on again.

Researchers find way to measure speed of spinning object using light's orbital angular momentum

Researchers find way to measure speed of spinning object using light's orbital angular momentum: In this new effort, the researchers found a way to measure the spin speed of an object that is not observed at an angle by taking advantage of a characteristic of light known as orbital angular momentum (OAM). This is where electromagnetic energy associated with light flows forward in the direction of propagation while also continuously moving around its own axis. In essence, it's light moving through space like a corkscrew. The researchers found that light can be imbued with OAM if it is reflected off a rotating object and it was this discovery that led to its use in calculating the spin speed of the object. Specifically, they found they could calculate the spin speed of the object by measuring the OAM in the light that has been reflected back by it.

To test their theory, the researchers fired a laser at a spinning plate in their lab then used a light detector to measure the degree of OAM. Because the plate was spinning, it gave off both positive and negative OAM—the degree of difference between the two gave the researchers the speed of rotation of the object.

The Hunt for the Magnetic Monopole - IEEE Spectrum

The Hunt for the Magnetic Monopole - IEEE Spectrum: The team proposed looking for these trapped monopoles at temperatures close to absolute zero in spin ice, a peculiar class of materials with ions arranged in four-sided pyramids called tetrahedra. These tetrahedra are stacked together to make a crystal called a pyrochlore.

The atoms at each corner of the pyramids in a pyrochlore are magnetic dipoles. Just like a bar magnet, they have a magnetic field that emerges from one side (what physicists tend to call “north” by convention) and curves around the atom so that it eventually enters the opposite end (“south”)....

When the temperature of the crystalline material is relatively high, the forces that try to align the spins are easily overwhelmed by thermal fluctuations. The spins are oriented at random and can easily change direction. When the material is cooled to just a few degrees above absolute zero, the forces between spins begin to dominate...

In the case where ice rules are obeyed, the two north poles and two south poles cancel each other out. But here’s where it gets interesting: When the ice rules are not obeyed—if, for example, there are three spins pointing inward and one pointing outward—then the three north poles and one south pole in the center will give rise to a single, north magnetic pole.

Artificial magnetic monopoles discovered

Artificial magnetic monopoles discovered: What happens, however, within the materials? Measurements taken by the group working under the direction of Prof. Pfleiderer in Munich using neutron scattering suggest that similar processes occur there, but individual whirls were not observed in this manner. For this reason, Stefan Buhrandt and Christoph Schütte working in Prof. Rosch's group at the University of Cologne conducted computer simulations. These showed that the whirls neighbouring the merging process observed on the surface in the experiment also occur within the materials...


Due to the fact that every whirl carries an artificial magnetic field, their creation or destruction occurs at the point of merging. "This means that an artificial magnetic monopole has to sit on this point," describes Prof. Rosch, "whenever two magnetic whirls merge in the experiment, an artificial magnetic monopole has flown through surface."

Material low-temperature properties can be predicted from its symmetry

Material low-temperature properties can be predicted from its symmetry: In the 1960s, physicists derived a counting rule for relativistic systems—those in which particles travel at close to the speed of light. This rule, called the Nambu–Goldstone theorem, says that the number of allowed disturbances equals the number of symmetries broken in a phase transition.

Hidaka was interested in finding a more general version of this rule that would apply to non-relativistic systems like solids or liquids—something that theorists have been trying to do for 50 years. He succeeded by adapting a theory used to describe the statistical motion of particles.

Simulation shows it's possible to move H2O@C60 using electrical charge

Simulation shows it's possible to move H2O@C60 using electrical charge: After embedding the water molecule inside the fullerene, the researchers simulated putting the new structure inside of a carbon nanotube, essentially creating a channel to allow for movement of the fullerene along with its water molecule cargo. They then applied an electrical charge parallel to the nanotube. Doing so, the researchers found, caused the fullerene to move within the channel (and the water molecule inside to spin), carrying its cargo with it...
Interestingly, the researchers found that if the charge was increased to 0.065 volts per angstrom, the direction of movement in the channel was reversed, though they can't explain why.

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.

‘Point of no return’ found | Harvard Gazette

‘Point of no return’ found | Harvard Gazette: According to Einstein’s theory of general relativity, a black hole’s mass and spin determine how close material can orbit before becoming unstable and falling in toward the event horizon. The team was able to measure this innermost stable orbit and found that it’s only 5.5 times the size of the black hole’s event horizon. This size suggests that the accretion disk is spinning in the same direction as the black hole.

Spin waves revealed in two-dimensional high-temperature superconductors

Spin waves revealed in two-dimensional high-temperature superconductors: Using a technique called resonant inelastic x-ray scattering (RIXS), scientists examined the magnetic spins of atomically thin layers of copper oxide materials. In a surprising discovery published in the journal Nature Materials on Sept. 2, researchers found that the spin waves present in complete, three-dimensional samples survived all the way down to the atomic level.

"For the first time, we can study truly two-dimensional behavior without the complicated interactions found on larger materials," said Brookhaven physicist Mark Dean. "It's widely believed that the essential electron pairing in high-temperature superconductors is magnetically mediated. Examining the fundamental building blocks of these superconductors, layers of copper and oxygen atoms, is key to understanding that magnetism and one day designing superconductors with even better properties."

A one-way street for spinning atoms

A one-way street for spinning atoms: In previous experiments, the RLE researchers created a superfluid — a completely frictionless gas — of lithium atoms. In their new experiment, the researchers used laser beams to trap a cloud of lithium atoms about 50 micrometers in diameter. The atoms were cooled to just a few billionths of a degree above absolute zero...

The researchers illuminated the gas with a pair of laser beams, sorting the atoms into two lanes, each of which consists of atoms with the same spin moving in the same direction. For the first time in an atomic system, this correlation of atoms’ spins with their velocities was directly measured.

“The combined system of ultracold atoms and the light we shine on them forms a material with unique properties,” says Lawrence Cheuk, lead author of the paper and a graduate student in MIT’s physics department. “The gas acts as a quantum diode, a device that regulates the flow of spin currents.”

Galactic 'axis of asymmetry' threatens cosmic order - New Scientist - New Scientist

Galactic 'axis of asymmetry' threatens cosmic order: In most directions, Longo found an even spread of right and left-handed galaxies. But when he looked along a line about 25 degrees off from the direction of the Milky Way's north pole - a cosmic reference point that sits directly above the centre of our galaxy - he found more left-handed spirals than right-handed ones...
Now, Lior Shamir of the Lawrence Technological University at Southfield, Michigan, has automated the process and looked deeper into space. His software classified the handedness of almost 250,000 spiral galaxies up to 3.4 billion light years away, which were surveyed by SDSS and another project called the Galaxy Zoo...

This time, though, the axis of asymmetry pointed about 60 degrees to the other side of the Milky Way's north pole (see diagram). Despite being separated by 85 degrees, both axes have such large uncertainties that they could be aspects of the same axis.
"The observation is so strange that it's difficult to interpret its meaning," says Shamir. "A pattern in the structure of the universe at such a large scale is not something that we expect to see."

Chemical bond discovered that only exists in space

Chemical bond discovered that only exists in space: The bond, of the chemical variety, occurs in the presence of very strong magnetic fields, such as those found around ultra-dense white dwarf stars...
They also exhibit super-strong magnetic fields on the order of 100,000 tesla – 10 billion times greater than Earth's magnetic field...

"Chemistry and molecular physics become very different in the presence of a strong magnetic field..."
With this in mind, the researchers used quantum chemical simulations to model chemical bonding in hydrogen and helium atoms in the magnetic field of a white dwarf. In both cases, the atoms were drawn into strongly bonded pairs.

Because the electrons in these bonded atoms occupied anti-bonding orbitals – which is forbidden in both types of known chemical bond – the researchers say this is a new type of bond. They have dubbed it "perpendicular paramagnetic bonding".

Astrophile: The case of the disappearing pulsar - New Scientist - New Scientist

Astrophile: The case of the disappearing pulsar: The star was a spectacular find: unlike every other pulsar ever observed, this one was in a close binary orbit with another pulsar. Together, the pair provided a precise laboratory to test Einstein's theory of general relativity, and a means of detailing how pulsars behave.
But in March 2008, Pulsar B went dark...
No one snuffed out Pulsar B – it just rotated out of view...

"We can see the light from one pulsar being bent as it travels through the gravitational well of the other pulsar," she says. "It's really neat. We have proof that one of these objects is distorting spacetime."
The eclipsing pulsars also provided a test of "spin precession", the idea that the pulsars' axes should wobble around like a top as they spin.

A Final Answer on How High-Temperature Superconductors Don't Work?

A Final Answer on How High-Temperature Superconductors Don't Work?: Tiny vibrations called phonons—the essential ingredient in the mechanism behind ordinary superconductors-play no significant role in high-temperature superconductivity, the team claims...

But theorists say phonons do not pull hard enough to keep electrons paired at the sky-high temperatures—which are still far below the freezing point of water—achieved in high-temperature superconductors. Instead, many think the glue originates in interactions among the electrons themselves, such as waves of magnetism called spin fluctuations...

The team hit the sample with a one-two punch of laser pulses roughly 100 millionths of a nanosecond, or 100 femtoseconds, long. The first pulse stirred up the electrons in the material; the second pulse measured how much the material's reflectivity had changed. The team was also able to trace the reaction not only in time, but also as a function of the frequency of the reflected light...

The ability to study the reflectivity at different wavelengths was key, Giannetti says. That's because the ultrafast electron-electron processes were too fast to observe in the time traces. However, those processes affect the reflectivity at different wavelengths in different ways—100 femtoseconds after the pulse the material was less reflective at longer wavelengths and more reflective at shorter wavelengths. Taken all together, the data show that phonons aren't needed to explain BSCCO's superconductivity, Giannetti says. Electron-electron interactions are strong enough to do the job all by themselves.

Starling Flocks Behave Like Flying Magnets | Wired Science | Wired.com

Starling Flocks Behave Like Flying Magnets | Wired Science | Wired.com: Rather than affecting every other flock member, orientation changes caused only a bird’s seven closest neighbors to alter their flight. That number stayed consistent regardless of flock density, making the equations “topological” rather than critical in nature.

“The orientations are not at a critical point,” said Giardina. Even without criticality, however, changes rippled quickly through flocks — from one starling to seven neighbors, each of which affected seven more neighbors, and so on.

The closest statistical fit for this behavior comes from the physics of magnetism, and describes how the electron spins of particles align with their neighbors as metals become magnetized.

Blog - Pulsars Are Giant Permanent Magnets, Say Physicists

Blog - Pulsars Are Giant Permanent Magnets, Say Physicists: Another problem is how pulsars end up with magnetic fields that are so strong. The conventional view is that the process of collapse during a supernova somehow concentrates the original star's field. However, a star loses much of its material when it explodes as a supernova and this presumably carries away much of its magnetic field too. But some pulsars have fields as high as 10^12 Tesla, far more than can be explained by this process.

Today, Johan Hansson and Anna Ponga at Lulea University of Technology in Sweden suggest a clever way out of this conundrum. They point out that there is another way for magnetic fields to form, other than the movement of charged particles. This other process is by the alignment of the magnetic fields of the body's components, which is how ferromagnets form.

Their suggestion is that when a neutron star forms, the neutron magnetic moments become aligned because this is the lowest energy configuration of the nuclear forces between them. When this alignment takes place, a powerful magnetic field effectively becomes frozen in place.