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.

New ‘switch’ could power quantum computing | MIT News Office

New ‘switch’ could power quantum computing | MIT News Office:  “We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom...”

In this case, the researchers used a laser to place a rubidium atom very close to the surface of a photonic crystal cavity, a structure of light. The atoms were placed no more than 100 or 200 nanometers — less than a wavelength of light — from the edge of the cavity. At such small distances, there is a strong attractive force between the atom and the surface of the light field, which the researchers used to trap the atom in place...

“In some sense, it was a big surprise how simple this solution was compared to the different techniques you might envision of getting the atoms there,” Vuletić says.

Physicists Net Fractal Butterfly: Scientific American

Physicists Net Fractal Butterfly: Scientific American: ...the pattern describes the behavior of electrons in extreme magnetic fields...

...It was known at the time that electrons under the influence of a magnetic field would race around in circles. But Hofstadter found that in theory, if the electrons were confined inside a crystalline atomic lattice, their motion would become complicated. As the magnetic field was cranked up, the energy levels that define the motion of electrons would split again and again. When represented on a graph, those energy levels revealed a pattern that looked like a butterfly — and continued to do so, even when zoomed in to infinitely small scales...

 In May, researchers reported that they had stacked a single sheet of graphene, in which carbon atoms are arranged like a honeycomb, on top of a sheet of honeycombed boron nitride. The layers create a repeating pattern that provides a larger target for magnetic fields than the hexagons in each material — effectively magnifying the field.

Precise atomic clock may redefine time : Nature News & Comment

Precise atomic clock may redefine time : Nature News: First, like trapped-ion clocks, they measure the frequency of visible light, with a frequency tens of thousands of times higher than that of microwaves. Second, they measure the average emission frequency from several thousand trapped atoms rather than just one, and so the measurement statistics are better. The atoms are trapped in an optical lattice, rather like an electromagnetic egg box for holding atoms.

If OLCs are to succeed, however, researchers must show that one such clock ticks at exactly the same rate as another prepared in an identical way. This is what Lodewyck and colleagues have shown. They prepared optical lattices that each held about 10,000 atoms of the isotope strontium-87, and have shown that the two clocks stay in synchrony to within a precision of at least 1.5 × 10−16, which is as accurately as the experiment could measure.

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.

Using laser beams, scientists generate quantum matter with novel, crystal-like properties

Using laser beams, scientists generate quantum matter with novel, crystal-like properties:  As the scientists chose Rydberg-states which give rise to repulsive van der Waals forces the excited atoms have to keep a minimum distance of several micrometers from each other. This mutual blockade leads to spatial correlations between the atoms such that, depending on the number of Rydberg-atoms, states with different geometrical configurations can emerge (see fig. 1). "However, we have to be aware that in our excited quantum system all geometrical orders are present at the same time. To be precise, all the excitation states form a coherent superposition, " Dr. Marc Cheneau says, a scientist at the experiment. "This new state of matter is a very fragile, crystal-like formation; it exists as long as the excitation is sustained, and fades away once the beam is switched off."

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.

BBC News - Ultracold science finds new method to get even colder

BBC News - Ultracold science finds new method to get even colder: The team carefully adjusted the intensity of the crossed light beams. The trick was to do so in such a way that only the most energetic atoms in each lattice site absorbed energy from the light fields, becoming more energetic again.

By adjusting how frequently the light beam intensities were changed, the team was able to remove these "hottest" atoms from the system, leaving only the "coolest" ones behind.

Chilled atoms are going to heat up scientific opportunities

Chilled atoms are going to heat up scientific opportunities: “Atomic lasers don’t sound that incredible, but they can be quite useful. Just like how the photons in a laser all have the same wavelength, the same polarization, the same direction—atoms do the same thing when they’re in BEC,” explains Aubin. “A BEC is like a laser for atoms.” Atomic lasers are more powerful than traditional lasers made of light. Because atoms have mass, atomic lasers are characterized by much shorter wavelengths...
An atomic laser also provides new ways to simulate solid-state systems. A resistor, transistor, superconductor, microchip or any solid-state system consists of solid crystals through which electrons flow. The crystals have inherent impurities that affect the flow of electrons. Aubin plans on using light lasers to create perfect crystal lattices through which BEC atoms, simulating electrons, will flow.

Lasers used to form 3-D crystals made of nanoparticles (w/ video)

Lasers used to form 3-D crystals made of nanoparticles (w/ video): The process involves shining laser beams through two opposed microscope lenses, one directly beneath the other. Two infrared laser beams are directed through each lens, and they meet at a common focal point on a microscope slide that holds thousands of plastic nanoparticles suspended in a drop of water.
The intersecting laser beams create electric fields that vary in strength in a regular pattern that forms a 3-D grid called an optical lattice. The nanoparticles get sucked into regions of high electric-field strength, and thousands of them align to form optically induced crystals. The crystals are spherical in shape and about 5 microns in diameter.

The 'quantum magnet': Physicists expand prospects for engineering unusual materials

The 'quantum magnet': Physicists expand prospects for engineering unusual materials: The problem is that what makes these materials useful often makes them extremely difficult to design,”said senior author Markus Greiner, an associate professor in Harvard’s Department of Physics. “They can become entangled, existing in multiple configurations at the same time. This hallmark of quantum mechanics is difficult for normal computers to represent, so we had to take another approach.”
That approach is using a so-called “quantum simulator” — the properties of a quantum material are simulated with an artificial quantum system that can behave similarly, but that is easier to manipulate and observe.

Atom images raise quantum computer hopes - physics-math - 18 August 2010 - New Scientist

Atom images raise quantum computer hopes: "Now two teams, one led by Stefan Kuhr of the Max Planck Institute for Quantum Optics in Garching, Germany, the other by Markus Greiner of Harvard University, have taken a first step by imaging the individual rubidium atoms in an optical lattice. This is a challenge not just because the atoms are tiny, but also because photons from nearby atoms can interfere with each other, smearing out any pattern.

To overcome this, the teams studied the light pattern from a single atom. They then created an algorithm which could generate a composite of this pattern from different arrangements of a grid of atoms. By matching these simulations to the actual pattern seen, the algorithm could determine the arrangement of atoms (Nature, DOI: 10.1038/nature09378, Science, DOI: 10.1126/science.1192368)."

An Atomic View of Quantum Phase Transitions -- DeMarco 329 (5991): 523 -- Science

An Atomic View of Quantum Phase Transitions -- DeMarco 329 (5991): 523 -- Science: An artificial solid is created in optical lattice experiments by first cooling atoms trapped as a gas in ultrahigh vacuum to nanokelvin temperatures (3). The atoms are twhen captured in a lattice that is created by slowly turning on a combination of laser beams. The atoms play the role of the electrons orsuperconducting pairs of electrons in a solid, whereas the light substitutes for the underlying ionic crystal. Different crystal geometries can be produced depending on the arrangement of the lasers. The holographic technique used by Bakr et al. to create a square lattice is especially powerful because it can, in principle, produce any two-dimensional crystal geometry."

UI group creates a disordered insulator in an optical lattice | Engineering at Illinois

UI group creates a disordered insulator in an optical lattice | Engineering at Illinois: "This approach—using one quantum system that we can control to elucidate another system that is beyond microscopic control—is called ‘quantum simulation’ and goes back to an idea first proposed by Richard Feynman in 1962.

“The microscopic effects of lattice defects and long-range electronic interactions, for example, are not well controlled in strongly correlated materials, and sophisticated theoretical approaches have reached inconsistent conclusions,” said DeMarco. “Simulating the impact of these effects on strongly correlated materials above absolute zero temperature is beyond the capabilities of even today’s supercomputers.”"

Pinning atoms into order

Pinning atoms into order: In an international first, physicists of the University of Innsbruck, Austria have experimentally observed a quantum phenomenon, where an arbitrarily weak perturbation causes atoms to build an organized structure from an initially unorganized one. The scientific team headed by Hanns-Christoph Nägerl has published a paper about quantum phase transitions in a one dimensional quantum lattice in the scientific journal Nature.