Cosmologists Say Last Week’s Announcement About Gravitational Waves and Inflation May Be Wrong — The Physics arXiv Blog — Medium

Cosmologists Say Last Week’s Announcement About Gravitational Waves and Inflation May Be Wrong — The Physics arXiv Blog — Medium: Many cosmologists think that the same kind of phases changes occurred in the universe after inflation. Each phase change began in different regions at slightly different times...

This self-ordering process would have been hugely violent, generating its own gravitational waves that rippled through spacetime, albeit after inflation. Could this process be responsible for the polarisation that the BICEP2 team has measured?...

...a small improvement in the data could firmly rule out self-ordering as the origin of the signal.

Pseudogap theory puts physicists closer to high temperature superconductors

Pseudogap theory puts physicists closer to high temperature superconductors: The theory explains the transition phase to superconductivity, or "pseudogap" phase, which is one of the last obstacles to developing the next generation of superconductors and one of the major unsolved problems of theoretical condensed matter physics...

This new study found that YBa2Cu3O6+x oscillates between two quantum states during the pseudogap, one of which involves charge-density wave fluctuations. These periodic fluctuations in the distribution of the electrical charges are what destabilize the superconducting state above the critical temperature.

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.

A Micro-Muscular Break Through � Berkeley Lab News Center

A Micro-Muscular Break Through � Berkeley Lab News Center: ...a micro-sized robotic torsional muscle/motor made from vanadium dioxide that for its size is a thousand times more powerful than a human muscle, able to catapult objects 50 times heavier than itself over a distance five times its length within 60 milliseconds...

Wu and his colleagues fabricated their micro-muscle on a silicon substrate from a long “V-shaped” bimorph ribbon comprised of chromium and vanadium dioxide. When the V-shaped ribbon is released from the substrate it forms a helix consisting of a dual coil that is connected at either end to chromium electrode pads. Heating the dual coil actuates it, turning it into either a micro-catapult, in which an object held in the coil is hurled when the coil is actuated, or a proximity sensor, in which the remote sensing of an object (meaning without touching it) causes a “micro-explosion,” a rapid change in the micro-muscle’s resistance and shape that pushes the object away...

The vanadium dioxide micro-muscles demonstrated reversible  torsional motion over one million cycles with no degradation. They also showed a rotational speed of up to approximately 200,000 rpm, amplitude of 500 to 2,000 degrees per millimeters in length, and an energy power density up to approximately 39 kilowatts/kilogram.

Material looks cool while heating up | Science News

Material looks cool while heating up | Science News:  The compound vanadium dioxide makes such a transition around 70o Celsius, switching abruptly from being an electrical insulator to a conductor...

... the researchers heated the vanadium dioxide-sapphire sample and, with an infrared camera, measured how much infrared light the sample emitted as it warmed. The color gradually shifted from blue to red as the sample's temperature increased from 60o to 74o, as is typical for a warming object. But then something strange happened: Even though the sample’s temperature continued to rise up to 100o, the camera readout returned to an icy blue and stayed there.

Bizarre Liquid More Stable Than Solid Crystal | LiveScience

Bizarre Liquid More Stable Than Solid Crystal | LiveScience: "When we make the bonds more flexible, the liquid phase remains stable even at extremely low temperatures," Smallenburg said. "The particles will simply never order into a crystal, unless they are compressed to high densities." �

What does mercury being liquid at room temperature have to do with Einstein’s theory of relativity? | The Curious Wavefunction, Scientific American Blog Network

What does mercury being liquid at room temperature have to do with Einstein’s theory of relativity? | The Curious Wavefunction, Scientific American Blog Network:  From Niels Bohr’s theory of atomic structure we know that the velocity of an electron is proportional to the atomic number of an element. For light elements like hydrogen (atomic number 1) the velocity is insignificant compared to the speed of light so relativity can be essentially ignored. But for the 1s electron of mercury (atomic number 80) this effect becomes significant; the electron approaches about 58% of the speed of light, and its mass increases to 1.23 times its rest mass. Relativity has kicked in. Since the radius of an electron orbit in the Bohr theory (orbital to be precise) goes inversely as the mass, this mass increase results in a 23% decrease in the orbital radius. This shrinkage makes a world of difference since it results in stronger attraction between the nucleus and the electrons, and this effect translates to the outermost 6s orbital as well as to other orbitals. The effect is compounded by the more diffuse d and f orbitals insufficiently shielding the s electrons. Combined with the filled nature of the 6s orbital, the relativistic shrinkage makes mercury very reluctant indeed to share its outermost electrons and form strong bonds with other mercury atoms.

The bonding between mercury atoms in small clusters thus mainly results from weak Van der Waals forces which arise from local charge fluctuations in neighboring atoms rather than the sharing of electrons.

'Liquid-liquid' phase transition: Researchers identify transformation in low-temperature water

'Liquid-liquid' phase transition: Researchers identify transformation in low-temperature water; Through a simulation performed in "supercooled" water, a research team led by chemist Feng "Seymour" Wang, confirmed a "liquid-liquid" phase transition at 207 Kelvins, or 87 degrees below zero on the Fahrenheit scale.
The properties of supercooled water are important for understanding basic processes during cryoprotection, which is the preservation of tissue or cells by liquid nitrogen so they can be thawed without damaged...

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.

Superheated Bose-Einstein condensate exists above critical temperature

Superheated Bose-Einstein condensate exists above critical temperature: In BECs and distilled water, the inhibition of a phase transition at the critical temperature occurs for different reasons. In general, there are two types of phase transitions. The boiling of water is a first-order phase transition, and it can be inhibited in clean water because, in the absence of impurities, there is in an energy barrier that "protects" the liquid from boiling away. On the other hand, boiling a BEC is a second-order phase transition. In this case, superheating occurs because the BEC component and the remaining thermal (non-condensed) component decouple and evolve as two separate equilibrium systems...


Here, the researchers demonstrated that in an optically trapped potassium-39 gas the strength of interactions can be reduced just enough so that the two components remain at the same temperature, but the particle flow between them is slowed down and their chemical potentials decouple. This condition makes it possible for the BEC to maintain a higher chemical potential than the surrounding thermal component, and thus survive far above its equilibrium transition temperature...



In the new study, the physicists experimentally demonstrated that a BEC could persist in the superheated regime... for more than a minute.

Solid or Liquid? Physicists Redefine States of Matter

Solid or Liquid? Physicists Redefine States of Matter: ...the main difference between liquids and solids is the way they respond to shear, or twisting forces. Liquids barely resist shear and can easily be sloshed, whereas solids — regardless of whether they are crystals, quasicrystals or glass — resist attempts to change their shape.

The liquid-solid phase transition, Radin and Aristoff reason, should therefore be marked by the “shear response” of a material jumping from zero to a positive value...

Topology: The Secret Ingredient In The Latest Theory of Everything

Topology: The Secret Ingredient In The Latest Theory of Everything: Today, Wen combines topology, symmetry and quantum mechanics in a new theory that predicts the existence of new states of matter, unifies various puzzling phenomena in solid state physics and allows the creation artificial vacuums populated with artificial photons and electrons...

Xiao-Gang Wen's approach is to explore the properties of matter when the topological links between particles become much more general and complex. He generalises these links, thinking of them as strings that can connect many  particles together. In fact, he considers the way many strings can form net-like structures that have their own emergent properties...
That makes string nets a kind of "quantum ether" through which electromagnetic waves travel. That's a big claim.

Ray of light could lead to next generation of superconductors

Ray of light could lead to next generation of superconductors: ...by manipulating different types of light, including UV and visible light, he and his fellow researchers are able to alter the critical temperatures of superconducting materials...

In the lab, they put a thin layer, one organic molecule thick, atop a superconducting film, approximately 50 nanometers thick. When researchers shined a light on these molecules, the molecules stretched and changed shape, altering the properties of the superconducting film—most importantly, altering the critical temperature at which the material acted as a superconductor. The researchers tested three separate molecules. The first was able to increase the critical temperature of the superconducting film. With the second molecule, they found that shining an ultraviolet light heightened the material's critical temperature, while visible light lowered it. Finally, with the third molecule, they found that simply by turning a light on, critical temperature was raised—and lowered again when the light was switched off.

Soft autonomous robot inches along like an earthworm - MIT News Office

Soft autonomous robot inches along like an earthworm - MIT News Office: Now researchers at MIT, Harvard University and Seoul National University have engineered a soft autonomous robot that moves via peristalsis, crawling across surfaces by contracting segments of its body, much like an earthworm. The robot, made almost entirely of soft materials, is remarkably resilient: Even when stepped upon or bludgeoned with a hammer, the robot is able to inch away, unscathed...
The robot is named “Meshworm” for the flexible, meshlike tube that makes up its body. Researchers created “artificial muscle” from wire made of nickel and titanium — a shape-memory alloy that stretches and contracts with heat. They wound the wire around the tube, creating segments along its length, much like the segments of an earthworm. They then applied a small current to the segments of wire, squeezing the mesh tube and propelling the robot forward...

YaleNews | Diamond in the rough: Half-century puzzle solved

YaleNews | Diamond in the rough: Half-century puzzle solved: A Yale-led team of mineral physicists has for the first time confirmed through high-pressure experiments the structure of cold-compressed graphite, a form of carbon that is comparable in hardness to its cousin, diamond, but only requires pressure to synthesize...
Researchers say this intermediate structure has much lower symmetry than diamond, but is as hard. In fact, “Our study shows that M-carbon is extremely incompressible and hard, rivaling the extreme properties of diamond so much that it damages diamond...”

Freezing magnetic monopoles: How dipoles become monopoles and vice versa

Freezing magnetic monopoles: How dipoles become monopoles and vice versa: "Steady flows of magnetic monopoles are apparently impossible," Powell said, "but transient currents have been demonstrated, and one could imagine creating an alternating current, the magnetic equivalent of AC electricity..."

Normally all magnetic poles should be confined within two-pole couplets---the traditional magnetic dipole. However, at a low enough temperature, around 5 K, "frustration" among the magnetic atoms---they want to align with each other but can't because of the inherent geometry of the material---leads to a disordered state with strong, synchronized fluctuations. Unpaired magnetic poles can form amid this tumult. That is, particles (quasiparticle excitations, to be exact) in spin ice with a net magnetic "charge" can exist and move about. A gas of electric charges is called a "plasma," so some scientists refer to the analogous tenuous cloud of magnetic charges as a "monopole plasma."
Stephen Powell's paper, published presently in the journal Physical Review Letters, explores what happens when the fluctuations are frozen by, for example, still-colder temperatures or a high-strength magnetic field. He shows how the monopoles are confined into magnetically neutral dipoles again. He is the first to prescribe the phase transition from the monopole phase (also called the Coulomb phase since the monopoles feel the same inverse-square force effect as electric charges) into the pole-confined phase.

Quantum Horse Races and Crystals of Light

Quantum Horse Races and Crystals of Light: Bloch’s team and others bring them to heel by cooling them to a temperature of nanokelvins and pouring them into an optical lattice, which, depending on your poetic frame of mind, you might call an optical egg crate or a crystal of light... The atoms are spaced perhaps 400 nanometers apart, so they reach a density of about 100 trillion atoms per cubic centimeter—which is a lot of atoms per cubic centimeter, but still only about a hundred-thousandth the density of hydrogen gas at room temperature and pressure. So these systems let physicists explore a domain they seldom otherwise enter, a frigid, sparse realm where quantum is king...

There are all sorts of other fun experiments you can do. Last year, Bloch’s team tracked the insulator-superfluid transition and showed that the system goes through a “hidden” phase of matter—a subtly patterned arrangement that conventional theory doesn’t capture...

Yet another experiment touches on the fundamental question of what determines the speed of events in the world... They began with an insulator, dialed up the interaction energy, and watched the atoms start to self-organize. A wave of activity spread though the system at twice the speed of sound. What governed the velocity was that atoms did not passively roll on the wave, but actively contributed to it. Some quantum gravity theorists have speculated that the speed of light represents the Lieb-Robinson bound of some underlying quantum system out of which space and time emerge.

Iron-based high-temp superconductors show unexpected electronic asymmetry

Iron-based high-temp superconductors show unexpected electronic asymmetry: Prior studies have shown that as HTS materials are cooled, they pass through a series of intermediate electronic phases before they reach the superconducting phase. To help see these "phase changes" at a glance, physicists like Nevidomskyy often use graphs called "phase diagrams" that show the particular phase an HTS will occupy based on its temperature and chemical doping.
"With this new evidence, it is clear that the nematicity exists all the way into the superconducting region and not just in the vicinity of the magnetic phase, as it had been previously understood," said Nevidomskyy, in reference to the line representing the boundary of the nematic order. "Perhaps the biggest discovery of this study is that this line extends all the way to the superconducting phase."
He said another intriguing result is that the phase diagram for the barium iron arsenide bears a striking resemblance to the phase diagram for copper-based high-temperature superconductors.

Is Dark Matter a Glimpse of a Deeper Level of Reality?

Is Dark Matter a Glimpse of a Deeper Level of Reality?: Black holes provide the strongest argument for this point of view. The laws of gravity predict that these cosmic vacuum cleaners obey versions of the laws of thermodynamics, which is strange, because thermodynamics is the branch of physics that describes composite systems, such as gases made up of molecules. A black hole sure doesn’t look like a composite system. It just looks like a warped region of space that you would do well to stay away from. For it to be composite, space itself must be.

In that case, black holes represent a new phase of matter. Outside the hole, the universe’s “degrees of freedom”—all that its most fundamental building blocks are capable of—are in a low-energy state, forming what you might think of as a crystal, with a fixed, regular arrangement we perceive as the spacetime continuum. But inside the hole, conditions become so extreme that the continuum breaks apart. “You can make spacetime melt,” Verlinde told me. “This is really where spacetime ends. To understand what goes on, you need to use these underlying degrees of freedom.” Those degrees of freedom cannot be thought of as existing in one place or another. They transcend space. Their true venue is a ginormous abstract realm of possibilities—in the jargon, a “phase space” commensurate with their almost unimaginably rich repertoire of behaviors.

First Simulation Of Quantum Tunnelling On A Quantum Computer - Technology Review

First Simulation Of Quantum Tunnelling On A Quantum Computer - Technology Review: The problem is the sheer complexity of these calculations, which require numerous quantum logic gates processing dozens of qubits. That's always been beyond the state-of-the-art for quantum computing.

Earlier this year, however, Andrew Sornborger at the University of Georgia in Athens showed how  the case of a single particle tunnelling through a barrier could be made simple enough to simulate on today's quantum computers. Such a demonstration would be the first example of a digital quantum simulation.

And today Guan Ru Feng and pals at Tsinghua University in Beijing say they've done it. To simulate tunnelling, these guys used a quantum computer that relies on nuclear magnetic resonance to manipulate qubits in encoded in the carbon and hydrogen atoms that make up chloroform molecules. They say this  is the first demonstration of a quantum tunnelling simulation using an NMR quantum computer.