Quantumaniac

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The Surface of Mars

Fullerenes and Buckyballs

Despite the seemingly complex name, a fullerene is nothing more than a molecule composed entirely of carbon. That’s all! Fullerenes can come in the shape of a hollow sphere, ellipsoid or tube. When a fullerene is spherical, they are known as buckyballs - and when cylindrical they are called carbon nanotubes or can be affectionately called buckytubes. Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings.

The first fullerene to be discovered, buckminsterfullerene (C₆₀), was prepared in 1985 by Richard Smalley, Robert Curl, James Heath, Sean O’Brien, and Harold Kroto at Rice University. The name was an homage to Buckminster Fuller, whose geodesic domes it resembles. The structure was also identified some five years earlier by Sumio Iijima, from an electron microscope image, where it formed the core of a “bucky onion.” Fullerenes have since been found to occur in nature. More recently, fullerenes have been detected in outer space. According to astronomer Letizia Stanghellini, “It’s possible that buckyballs from outer space provided seeds for life on Earth.”

The discovery of fullerenes greatly expanded the number of known carbon allotropes, which until recently were limited to graphite, diamond, andamorphous carbon such as soot and charcoal. Buckyballs and buckytubes have been the subject of intense research, both for their unique chemistry and for their technological applications, especially in materials science, electronics, and nanotechnology.

Bionic Penguins

In 2009, a German Engineering Firm, Festo, developed two colonies of bionic penguins that are able to demonstrate collective behavior. The penguins can utilize their flippers and swim smoothly through the water just like real ones, and larger models filled with helium are able to fly and “swim” through the sky. The penguins contain a 3D sonar system, which is used to monitor its surroundings and avoid collisions. 

Flexible glass fibre rods were used to control the heads, which enables graceful, smooth head turns. “The fibres are arranged around the side of each penguin’s head, while motors inside the body pull on one or more of them to twist the penguin’s neck in any direction and guide the swimmer, says Markus Fischer, who heads Festo’s corporate design team.”

The penguins are also able to collectively work together in a group, exhibiting what psychologists know as “crowd behavior,” in which one member can respond and react to what another does. 

You can watch the video here. 

Generating matter and antimatter from the vacuum

The Compact Muon Solenoid (CMS) at CERN

New Kind of Quantum Junction

A new type of quantum bit called a “phase-slip qubit,” devised by researchers at the RIKEN Advanced Science Institute and their collaborators, has enabled the world’s first-ever experimental demonstration of coherent quantum phase slip (CQPS). The groundbreaking result sheds light on an elusive phenomenon whose existence — a natural outcome of the hundred-year-old theory of superconductivity — has long been speculated, but never actually observed.

Researchers have long known of an intriguing theoretical parallel to the Josephson effect in which insulator and superconductor are reversed: rather than electric charges jumping from one superconducting layer to another across an insulating layer, magnetic flux quanta jump from one insulator to another across a superconducting layer. Quantum tunneling of electrons in the Josephson junction is replaced in this parallel by the coherent “slip” of the phase, a quantum variable that, in superconducting circuits, plays a dual role to that of electric charge.

Coherent quantum phase slip (CQPS), as this phenomenon is known, has long been limited to theory — but no more. In a paper in Nature, Oleg Astafiev and colleagues at the RIKEN Advanced Science Institute (ASI) and NEC Smart Energy Research Laboratories report on the first direct observation of CQPS in a narrow superconducting wire of indium-oxide (InOx). The wire is inserted into a larger superconducting loop to form a new device called a phase-slip qubit, with the superconducting layer (the thin wire) sandwiched between insulating layers of empty space.

By tuning the magnetic flux penetrating this loop while scanning microwave frequencies, the researchers detected a band gap in the energy curves for the two flux states of the system, just as theory predicts. This gap is a result of quantum mechanics, which prevents the two states from occupying the same energy level, forcing them to tunnel across the superconducting layer — and through a quantum phase-slip in the narrow wire — to avoid it. While demonstrating conclusively the existence of CQPS, the successful experiment also ushers in a novel class of devices that exploit the unique functionality of quantum phase-slip to forge a new path in superconducting electronics.

(Source: sciencedaily.com)

Physicists Explain the Collective Motion of Fermions

Some people like company. Others prefer to be alone. The same holds true for the particles that constitute the matter around us: Some, called bosons, like to act in unison with others. Others, called fermions, have a mind of their own.

Different as they are, both species can show “collective” behavior — an effect similar to the wave at a baseball game, where all spectators carry out the same motion regardless of whether they like each other.

Scientists generally believed that such collective behavior, while commonplace for bosons, only appeared in fermions moving in unison at very long wavelengths. Now, however, collective behavior has been discovered at short wavelengths in one Fermi system, helium-3.

A team led by Professor Eckhard Krotscheck — a physicist who recently joined the University at Buffalo from the Johannes Kepler University in Linz, Austria — predicted the existence of the behavior using theoretical tools. Independently, but practically at the same time, a French team observed the collective behavior.

A paper detailing both the theoretical and experimental discoveries appeared in the journal Nature on March 29.

Krotscheck said the scientists’ success in developing accurate theoretical predictions lay, in part, in the fact that they focused on mathematical tools instead of trying to reproduce experiments.

“Knowing how nature ticks at a microscopic scale, we set out to develop a robust theory that was capable of dealing with a wide range of situations and systems,” Krotscheck said. “We demanded that our mathematical description is accurate for both fermions and bosons, in different dimensions, and for both coherent and incoherent excitations. Only after we were done, we looked at experiments.”

Physicists Proposes a New Way to Tune Instruments

By minimizing the entropy in the sound waves produced by a musical instrument it might be possible to use an electronic device to tune that instrument as well as is possible with the best human ear. So says a German physicist who has found that seemingly random fluctuations in the pitch difference between successive keys in a tuned upright piano may in fact be crucial to a harmonious sound.

The system of tuning used in most Western musical scales is known as “equal temperament”, which means that the ratio of frequencies of successive notes in the scale is a constant. Since the pitch doubles every 12 notes, the frequency ratio between neighbouring notes is 2^1/12. Intuitively, it might be expected that tuning a piano or other keyboard instrument is then simply a question of ensuring that this ratio holds for every pair of adjacent notes. However, this would only be true for pianos with perfect strings – those that have no stiffness.

In practice, the higher-frequency modes, or “harmonics”, that always accompany a note of a particular fundamental frequency, and which provide an instrument with its characteristic sound, deviate from their theoretical frequency values. This means that where they ought to coincide and produce a harmonious sound, harmonics from different notes that are played together are instead out of step and produce a series of unpleasant beats.

Professional aural tuners overcome this problem by “stretching” intervals – slightly increasing the pitch of higher notes to ensure their harmonics are never too far below those of lower-frequency notes while marginally decreasing the pitch of the lower notes. 

Haye Hinrichsen, a statistical physicist at the University of Würzburg, wondered whether these irregularities were random and the result of the limitations of human hearing or whether they might, on the contrary, be vital for good tuning. He also speculated that entropy was the key to reproducing these fluctuations systematically. Here, entropy refers to the amount of information needed to describe a physical state. When two harmonics from different notes overlap, less information is needed to describe their combined state than if they were to remain distinct, which means they have a lower entropy. So Hinrichsen hypothesized that maximizing tuning means minimizing entropy.

He began by recording the waveforms produced by each of the 88 keys on his piano. He used a computer program to apply a Fourier transform to each waveform, giving him a series of peaks on a plot of intensity versus frequency. He then “detuned” the resulting spectrum so that it formed a scale of equal temperament, with the fundamental frequency of each note being 2^1/12 times higher than the preceding one, and then he added all 88 plots together. Next, he applied an algorithm to work out the spectrum’s entropy, then randomly increased or decreased the pitch of one of the 88 notes by a small amount. If as a result of this change the spectrum’s entropy dropped, then the change was kept, otherwise it was rejected. The pitch of another note chosen at random was then changed and the cycle repeated until the entropy could be reduced no more.

Hinrichsen was able to produce tuning curves very similar to those from the aural tuning. As he points out, not only does it reproduce the overall shape of the curve but it also recreates many of the individual fluctuations. He believes that it might therefore be possible to produce a new kind of hybrid electronic device that uses conventional harmonics-matching to generate a smooth tuning curve and that then uses entropy minimization to produce the all-important detail. He explains that the entropy technique is probably not suitable for use on its own because it yields local rather than global minima, potentially causing the system to get locked into higher or lower notes than it should. He also points out that the approach remains unproven, because he has so far tested it on just one piano and because he has not shown it to work using small subsets of notes, which is the approach taken by professional tuners.