Guido Meier at the University of Hamburg in Germany and colleagues used nanosecond pulses of electric current to push magnetic regions along a wire at 110 metres per second – a hundred times faster than was previously possible.

By contrast, today’s hard drives rely on the much slower spinning motion of a disk to move magnetic regions – and the data encoded by these regions – past a component that can change or “read” this magnetic information.

“If you want to make a hard drive, operating speed is an important factor,” says Meier. “The idea is also to get rid of the mechanical parts, so there’s much less wear and tear, and devices can become more robust.”

The idea of moving magnetically-stored data electronically has been touted before. Stuart Parkin at IBM Almaden Research Center in San Jose, California, patented a similar concept called a magnetic “racetrack” in 2004.

Round the bend

In his device, a U-shaped magnetic nanowire is embedded into a silicon chip. Magnetic domains are then moved along the wire by pulses of polarised current, and are read by fixed sensors arranged in the silicon itself.

According to IBM, this type of magnetic memory could vastly simplify computers, and eventually replace all hard-disk drives. However, previous experiments have disappointed, producing speeds up to a thousand times slower than predicted.

“Our results showed the movement of domains cannot be predicted with certainty as they get stuck on imperfections in the crystal,” says Meier. “We believe this is why previous attempts were relatively slow as they used longer electric current pulses – up to microseconds long – increasing their chances of getting stuck.”

Aligned atoms

By switching powerful magnetic fields on and off, the researchers were able to rapidly create magnetic domains in a wire less than a micron wide made of permalloy – a magnetic material made of iron and nickel that is often found in disk drives.

These regions contains many magnetic atoms all aligned in the same direction and are separated by domain walls – thin regions where the atoms change their magnetic orientation from one alignment to the other. These can then be moved using much shorter nanoscale pulses.

A powerful x-ray microscope, capable of resolving features as small as 15 nanometres, was then used to read this information by snapping images of domain walls before and after the nanosecond current pulses. Future hard drives could store data by designating a domain wall to be a binary one, while its absence could be interpreted as a binary zero, the researchers say.

However, there are still problems that need to be overcome before the technique could be used more widely. In particular, small crystal imperfections in the wire impede progress, slowing down some domain walls and stopping others altogether.

“The question is can we fabricate media that are perfect or control the imperfections,” says Peter Fischer, a team member at Lawrence Berkeley National Laboratory, California. Meier believes that using different materials and changing the shape of the wire could help avoid these issues.

For the first time the birth, life and death of a single photon – a particle of light – has been “watched” in real time.

Previously, scientists were restricted to momentary glances because the mere act of measurement absorbed and destroyed the delicate quantum particles.

Now, Serge Haroche and colleagues at the École Normale Supérieure in Paris, France, have succeeded in tracking photons over an average lifetime of 0.13 seconds – long enough for a photon to travel one-tenth of the way to the Moon.

At the heart of their remarkable achievement lies a small box-like cavity, walled with ultra-reflective, superconducting mirrors, which is cooled to just 0.5° above absolute zero (-273.15°C). Photons appear and disappear randomly within the cavity due to tiny energy fluctuations in space that cause quantum particles to blink in and out of existence. However, once there, the photon is trapped, bouncing billions of times between the mirrored walls before it decays.

Trapped and annihilated

To observe the photon, the researchers passed rubidium atoms across the cavity one at a time. A single rubidium atom is unable to absorb a single photon, because the photon is not the correct package of energy to boost the rubidium atom to a different energy state.

However, the photon’s electric field slightly shifts the atom’s energy levels by a measurable amount (once the atom has emerged), which the team used to determine whether there were any trapped photons.

“This is not performed at the expense of the photon energy, so if one is detected, it is still there afterwards for successive rubidium atoms, allowing us to track it,” says Haroche. “A typical signal has a sequence of atoms at one energy level, meaning an empty cavity, suddenly interrupted by atoms at another energy level, signalling the photon birth. Later, a jump in the opposite direction signals the photon annihilation.”

“This is a very important fundamental achievement as no one has ever seen a photon a second time,” says Ferdinand Schmidt-Kaler at the University of Ulm in Germany. “It also has significant implications for the rapidly evolving field of quantum computing.”

Quantum computing relies on transferring qubits – quantum bits of information – between different energy states to vastly speed up calculations. According to Schmidt-Kaler, the results demonstrate a stream of atomic qubits can be fully controlled by the qubit state of a trapped photon – a notable achievement, since such operations are fundamental to quantum computers.

Journal reference: Nature (vol 446, p 297)

Trace chemicals ejected from the Sun and collected by NASA’s Genesis mission have solved a long-standing lunar mystery that threatened to rewrite our understanding of how the Sun evolved.

For the last 4 billion years, energetic solar particles have bombarded the Moon. But studies of these particles in rocks brought back by the Apollo astronauts have mystified scientists.

That is because the ratio of two isotopes of neon have varied according to depth in the rocks, with comparatively more neon-22 than neon-20 at lower depths. That suggested that counter to theory, the Sun had once been significantly more active than it is today, shooting out higher energy particles that could travel farther into the rocks.

Now, Ansgar Grimberg at the Swiss Federal Institute of Technology (ETH) in Zurich, and colleagues have resolved the conundrum.

They used nitric acid to strip away layers of a specially made metallic glass that had been exposed to the solar wind for 27 months on the Genesis spacecraft, which crashed to Earth in 2004.

When they measured the neon distribution in the exposed solar wind samples, they found the top layer had considerably higher proportions of neon-20 than observed in the lunar samples, while the underlying layers were similar to those seen in the Moon rocks.

That suggests that erosion from micrometeorites and space particles removed some of the original neon from the top surface of all lunar rocks.

More importantly, it also shows that the solar wind alone – not any extra activity on the Sun – can explain the puzzling neon variations in the Moon rocks, with the heavier neon-22 simply implanting itself more deeply than neon-20.

Journal reference: Science (vol 314, p 1133)

“The problem of fair division is one of the oldest existing problems. The cake is a metaphor for any divisible object where people value different parts differently,” explains Christian Klamler, at the University of Graz, Austria, who solved the problem with fellow mathematicians Steven Brams and Michael Jones.

According to Klamler, for any division to be acceptable, it must ideally be equal among all parties, envy-free so that no one prefers another’s share and equitable, where each places the same subjective value on their share.

Traditional methods, such as the “you cut, I choose” method, where one person halves the cake and the other chooses a piece, are flawed because though both get equal shares and neither is envious, the division is not equitable – one piece may have more icing or fruit on it than another, for example.

Impartial cutter

Enter the “Surplus Procedure” (SP) for cake-sharing between two people, and the “Equitability Procedure” (EP) for sharing between three or more. Both involve asking guests to tell the cake-cutter how they value different parts of the cake. For example, one guest may prefer chocolate, another may prefer marzipan.

Under SP, the two parties first receive just half of the cake portion that they subjectively valued the most. Then the “surplus” left over is divided proportionally according to the value they gave it. EP works in a similar way: the guests first get an equal proportion of the part of the cake they each value the highest – a third each if they are three; a quarter each if they are four, etc – and then the remainder is again divided along the lines of subjective value.

The result is everyone is left feeling happy, Klamler says. Two people, for example, may feel they are each getting 65% of what they want rather than just half.

“These procedures are new and have never been tried out in real-world applications,” says Brams. “But where there is a divisible good like land or water, which players value differently, the procedure could be used to allocate more-than-proportional shares, making everybody as happy as possible.”

Intriguingly, the procedures are “tamper-proof” – people cannot manipulate the process and must be truthful with the referee, or else they could end up with less than makes them happy.

Journal reference: Notices of the American Mathematical Society (Vol 53, p1014)

The pair were honoured for “their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation”, the jury said.

According to the big bang theory, the cosmos was formed from a cataclysmic explosion that happened about 13.7 billion years ago. The timescale and geometry are measurable by shockwaves called cosmic microwave background (CMB) that continues to wash over us.

Dubbed the “afterglow of creation”, the CMB is the earliest light in the universe. It is a faint aura of primordial radiation that comes to us directly from the early universe, just 380,000 years after the big bang. While it is spread very uniformly in the sky, scientists have observed tiny variations in the temperature and polarisation of the radiation, which they believe will reveal vital details about the size, matter content, age, geometry and fate of our universe.

These variations are also believed to contain information about the earliest moments of the universe, when it was rapidly expanding faster than light in a dizzying process known as inflation.

Cosmological breakthrough

Mather, 60, is an astrophysicist at NASA’s Goddard Space Flight Center in Maryland, and Smoot, 61, is a physicist at the University of California at Berkeley, both in the US.

The pair worked with the COBE satellite launched by NASA in 1989, and the results of their research added weight to the big bang scenario, since this is the only scenario that predicts the kind of cosmic microwave background radiation measured by COBE.

Smoot’s announcement in 1992 that his team had observed the long-sought variations in the CMB – and therefore, in the early universe – shook the scientific community. Called “the discovery of the century, if not of all time”, by Stephen Hawking, the discovery of these ripples and wrinkles in the very fabric of space-time are believed to be the primordial seeds of modern-day structures in our universe such as galaxies, clusters of galaxies, and so on.

“These measurements also marked the inception of cosmology as a precise science,” the Nobel jury said.

Dark matters

Mather coordinated the entire process and had responsibility for the experiment that revealed the blackbody form of the microwave background radiation measured by COBE. Smoot meanwhile had the main responsibility for measuring the small variations in the temperature of the radiation.

Since then, NASA has launched another probe, the Wilkinson Microwave Anisotropy Probe (WMAP), which is examining these minute variations in the CMB in even greater detail and has provided strong evidence for a universe dominated by mysterious dark matter and dark energy.

Other cosmologists have applauded the award. “Although COBE was a team effort and the CMB has been more fully elucidated by later experiments, Mather and Smoot are undoubtedly leading figures,” says Martin Rees, president of the UK’s Royal Society and the Astronomer Royal of England. “Had these fluctuations not been there, it would have been hard to account for the universe’s present structured state. Later experiments have refined this data, but the best measurement of the spectrum is still from COBE.”

This is not the first time work in the field has been rewarded by the Nobel committee. The 1978 Nobel prize for physics was awarded to Arno Penzias and Robert Wilson for detecting the CMB, back in 1965.

The 2006 laureates will each receive a gold medal and a diploma and will share a cheque for 10 million Swedish kronor ($1.37 million dollars) at the formal prize ceremony held, as tradition dictates, on December 10. It is the anniversary of the death of the prize’s creator Alfred Nobel, in 1896.