Long-range tunneling of quantum particles

Long-range tunneling of quantum particles: Experimental physicists in Innsbruck, Austria, have now directly observed quantum particles transmitting through a whole series of up to five potential barriers under conditions where a single particle could not do the move.

Particles near absolute zero do not break the laws of physics after all

Particles near absolute zero do not break the laws of physics after all: The authors focused on a model system favored by thermodynamics experts that consists of a free particle strongly coupled to a heat bath, representing the effect of its environment... Previous theoretical predictions suggested that, under certain circumstances, the specific heat can decrease below zero at a temperature of strictly zero (−273.15°C)...

...In fact, a real particle will always be confined to a finite volume—even if that volume may be extremely large. Therefore, they discovered that previous studies need to be modified in order to account for a spatial confinement of the particle...

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.

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.

Scientists create never-before-seen form of matter

Scientists create never-before-seen form of matter: What we have done is create a special type of medium in which photons interact with each other so strongly that they begin to act as though they have mass, and they bind together to form molecules...


An effect called a Rydberg blockade, Lukin said, which states that when an atom is excited, nearby atoms cannot be excited to the same degree. In practice, the effect means that as two photons enter the atomic cloud, the first excites an atom, but must move forward before the second photon can excite nearby atoms.

The result, he said, is that the two photons push and pull each other through the cloud as their energy is handed off from one atom to the next.

"It's a photonic interaction that's mediated by the atomic interaction..."

Ultracold Big Bang experiment successfully simulates evolution of early universe

Ultracold Big Bang experiment successfully simulates evolution of early universe: Physicists have reproduced a pattern resembling the cosmic microwave background radiation in a laboratory simulation of the Big Bang, using ultracold cesium atoms in a vacuum chamber at the University of Chicago...


It turns out that under certain conditions, a cloud of atoms chilled to a billionth of a degree above absolute zero (-459.67 degrees Fahrenheit) in a vacuum chamber displays phenomena similar to those that unfolded following the Big Bang, Hung said.

"At this ultracold temperature, atoms get excited collectively. They act as if they are sound waves in air," he said. The dense package of matter and radiation that existed in the very early universe generated similar sound-wave excitations, as revealed by COBE, WMAP and the other experiments.

The synchronized generation of sound waves correlates with cosmologists' speculations about inflation in the early universe. "Inflation set out the initial conditions for the early universe to create similar sound waves in the cosmic fluid formed by matter and radiation," Hung said.

Ultracold Big Bang experiment successfully simulates evolution of early universe | UChicago News

Ultracold Big Bang experiment successfully simulates evolution of early universe | UChicago News: These excitations are called Sakharov acoustic oscillations, named for Russian physicist Andrei Sakharov, who described the phenomenon in the 1960s. To produce Sakharov oscillations, Chin’s team chilled a flat, smooth cloud of 10,000 or so cesium atoms to a billionth of a degree above absolute zero, creating an exotic state of matter known as a two-dimensional atomic superfluid.

Then they initiated a quenching process that controlled the strength of the interaction between the atoms of the cloud. They found that by suddenly making the interactions weaker or stronger, they could generate Sakharov oscillations.

The universe simulated in Chin’s laboratory measured no more than 70 microns in diameter, approximately the diameter as a human hair.

NIST Ytterbium Atomic Clocks Set Record for Stability

NIST Ytterbium Atomic Clocks Set Record for Stability: The ytterbium clock ticks are stable to within less than two parts in 1 quintillion (1 followed by 18 zeros), roughly 10 times better than the previous best published results for other atomic clocks...
Each of NIST's ytterbium clocks relies on about 10,000 rare-earth atoms cooled to 10 microkelvin (10 millionths of a degree above absolute zero) and trapped in an optical lattice—a series of pancake-shaped wells made of laser light. Another laser that "ticks" 518 trillion times per second provokes a transition between two energy levels in the atoms. The large number of atoms is key to the clocks' high stability.
The ticks of any atomic clock must be averaged for some period to provide the best results. One key benefit of the very high stability of the ytterbium clocks is that precise results can be achieved very quickly. For example, the current U.S. civilian time standard, the NIST-F1 cesium fountain clock, must be averaged for about 400,000 seconds (about five days) to achieve its best performance. The new ytterbium clocks achieve that same result in about one second of averaging time.

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.

Google's Quantum Computer Proven To Be Real Thing (Almost) | Wired Enterprise | Wired.com

Google's Quantum Computer Proven To Be Real Thing (Almost) | Wired Enterprise | Wired.com


What they can say for sure is that the system doesn’t use simulated annealing, which is essentially a means of searching for a mathematical solution. According to Lidar, simulated annealing is akin to looking for the lowest possible point in a vast landscape.

“We call it an energy landscape,” he says. “There is a solution hiding somewhere in that landscape, and you can imagine that solution is hiding at the lowest point on the surface. You’re trying to find that lowest point.” This is done by randomly traveling across the landscape, moving down “hills” and back up them, until you locate the deepest valley.

This strategy relies purely on classical physics, not quantum physics. But Lidar says the D-wave is “consistent” with quantum annealing. This is similar to simulated annealing — except you can, in essence, go through the hills rather than over them. “You can take advantage of a quantum phenomenon called tunneling,” Lidar says. “It’s like a quantum shortcut.” He’s careful to say that he and his team have not proven that the D-Wave uses quantum annealing, but the system certainly appears to use it.

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.

Penetrating the quantum nature of magnetism

Penetrating the quantum nature of magnetism: he LQM scientists, led by Henrik M. Rønnow, cooled down a copper sulfate crystal close to absolute zero (about 0.01 K) to turn it into a quantum spin liquid and then used inelastic neutron scattering to investigate the motion of electrons' spins. The experiments reveal that the magnetic properties of copper sulfate can no longer be described by the individual behavior of the magnetic moments carried by each individual electron in the sample. Instead, flipping the magnetic moment of one single electron creates two spatially separated quantum objects called spinons.

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.

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.

Amherst Prof Devises First Head-to-Head Speed Test with Conventional Computing, and the Quantum Computer Wins | Amherst College

Amherst Prof Devises First Head-to-Head Speed Test with Conventional Computing, and the Quantum Computer Wins | Amherst College: McGeoch says the calculations the D-Wave excels at involve a specific combinatorial optimization problem, comparable in difficulty to the more famous “travelling salesperson” problem that’s been a foundation of theoretical computing for decades.

Creating time crystals with a rotating ion ring

Creating time crystals with a rotating ion ring: The Berkeley team, led by Xiang Zhang and Hartmut Häffner, will attempt to build a time crystal by introducing 100 calcium ions into a 100-micron wide ion trap. The calcium ions will be confined by electric fields to form a crystalline ring, which will then be induced to rotate under the influence of a static magnetic field. According to the group's calculations, this ring should settle into the ground state when the atoms are pre-cooled with lasers to around one-billionth of a degree above absolute zero...


The experimental plan is to properly cool the chamber and then apply the proper magnetic fields. At this point, the ions should begin to cycle around their starting point at regular intervals, forming the repeating lattice of the time crystal. To observe this ion rotation, one of the 100 calcium ions will then be toggled into a new electronic state using a laser. If the scientists observe that ion rotating at steady state, they will have in effect, "broken the translational symmetry of time."

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.

Physicists make discovery in the quantum realm by manipulating light

Physicists make discovery in the quantum realm by manipulating light: "In our experiment, we caught and released photons in and from a superconducting cavity by incorporating a superconducting switch," said Yin. "By controlling the switch on and off, we were able to open and close a door between the confined cavity and the road where photons can transmit. The on/off speed should be fast enough with a tuning time much shorter than the photon lifetime of the cavity." She explained that not only can the switch be in an on/off state, it also can be opened continuously, like a shutter. In that way, the research team was able to shape the released photons in different wave forms –– a key element for the next step they want to accomplish: controlled photon transfer between two distant cavities.

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.

Quantum gas goes below absolute zero : Nature News & Comment

Quantum gas goes below absolute zero : Nature News: 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...
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.