Do ultracold neutrons get a kick from nanoparticles?

Physics WorldJon Cartwright

Published in Physics World, 1 Oct 2013

Physicists in France and Russia claim to have evidence that explains why so-called ultracold neutrons (UCNs) escape their traps. The evidence suggests that the neutrons are being kicked out of the traps by collisions with floating nanoparticles and could help explain discrepancies in measurements of the neutron lifetime. However, not all scientists in the field find the evidence compelling.

UCNs are neutrons that have been cooled to less than 2 mK above absolute zero. At these temperatures the neutrons are moving so slowly that they would easily be overtaken by someone running at a moderate pace. UCNs bounce off most surfaces they come into contact with, regardless of their angle of incidence. This has allowed physicists to trap large numbers of UCNs in oversized “bottles” made of materials such as copper or stainless steel – where the neutrons can be studied. Neutrons experience all four forces – electromagnetism, the weak force, the strong force and gravity – which make them a comprehensive laboratory for tests of the Standard Model of particle physics. […]

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Has a quantum computer solved the ‘party problem’?

Physics WorldJon Cartwright

Published in Physics World, 27 Sep 2013

A quantum computer made by the Canadian company D-Wave Systems has been used to solve a famous puzzle in mathematics known as the party problem – according to a team of physicists in Canada and the US that has done the work. D-Wave describes the result as one of the most significant achievements for its devices to date, but some physicists are being party poopers by remaining unconvinced there is anything to boast about.

Unlike classical computers, which store bits of information in definite values of 0 or 1, quantum computers store information in quantum bits (qubits) that exist as a fuzzy superposition of both. This mixed-up nature of quantum computing extends beyond individual qubits: multiple qubits can be entangled so that they work in unison. As a result, quantum computers should be able to solve certain problems – such as factorizing large numbers – much faster than their classical counterparts. […]

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Why a Water Bridge Doesn’t Collapse

ScienceJon Cartwright

Published in Science, 23 Sep 2013

If you apply an electric voltage across two water-filled beakers and separate them, something strange happens: The water stretches from beaker to beaker, creating a bridge that defies gravity. Water bridges were discovered 120 years ago, but no one has ever been sure why they do not collapse. […]

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Molecules line up in laser grid

Physics WorldJon Cartwright

Published in Physics World, 18 Sep 2013

Physicists in the US have stored ultracold molecules in an optical lattice for the first time. The molecules – which interact with one another at a distance and not just at short range – could be used to study phenomena such as quantum magnetism, the researchers say.

When a system is cooled to a temperature very close to absolute zero, the underlying behaviour of its component parts is less erratic and it becomes possible to study their pure, quantum-mechanical interactions. For some three decades, physicists have studied ultracold atoms for this reason. However, many materials in nature are based on molecules, not atoms, and so physicists have been keen to study ultracold molecules too. […]

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Experiment probes strength of the weak interaction

Physics WorldJon Cartwright

Published in Physics World, 16 Sep 2013

An international collaboration has made the first determination of the proton’s “weak charge” – a quantity that is related to the strength of the weak interaction. The Q-weak experimental collaboration, working at Jefferson Lab in Newport News, Virginia, says that the small number of data analysed so far agree with predictions of the Standard Model of particle physics but that it believes a full analysis could still reveal the existence of “new physics”.

All the fundamental forces in nature have a strength that is determined by a certain particle parameter. For instance, the strength of gravity is determined by particle mass, while the strength of electromagnetism is determined by electric charge. Similarly, the strength of the weak force, which governs radioactive decay, is determined by a property known as weak charge. In fact, physicists have known that the electric and weak charges are related to one another since the late 1960s, when the electromagnetic and weak forces were unified into a single electroweak theory, which forms part of the Standard Model of particle physics. […]

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Seeking a Simpler Solar Cell

ScienceJon Cartwright

Published in Science, 13 Sep 2013

An efficient new solar-cell technology uses the same inexpensive manufacturing method as many silicon cells—suggesting that it could be easily adopted by industry. The technology uses a class of materials known as perovskites, in addition to other semi conductors. […]

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A Flat-Out Major Advance for an Emerging Solar Cell Technology

ScienceJon Cartwright

Published in Science, 11 Sep 2013

A promising solar cell material can be manufactured using the same method as the cheapest silicon devices, without sacrificing energy-production efficiency. The advance boosts the chances that the cheap material could be adopted by existing industry.

A solar cell converts sunlight into electricity. A typical cell contains layers of materials known as semiconductors—most often silicon. When a particle of light, or photon, strikes an atom in one of these semiconductors, it knocks free a negative electron that can scoot through the material and leaves behind a positively charged “hole” that can also move about. The electrons and holes travel in opposite directions, through layers of semiconductors with different properties, to create a flow of current. […]

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Laser imaging spots brain cancer

Physics WorldJon Cartwright

Published in Physics World, 6 Sep 2013

Researchers in the US have developed a new technique to distinguish tumours from healthy tissue in the brain. Based on stimulated Raman-scattering microscopy, the technique could boost the success rate for the complete surgical removal of brain tumours.

Normal cancer surgery on the brain starts with a magnetic-resonance image to plan the operation and to predict the location of the tumour. However, during the surgical procedure it is largely up to the surgeon to determine which tissue is tumorous and which is healthy. Tumorous tissue often feels different and has a different colour. But the differences are slight and for this reason more than 75% of brain-cancer patients are thought to leave theatre with a less-than-optimal amount of their tumour eradicated. […]

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Quantum cryptography reaches out to multiple users

Physics WorldJon Cartwright

Published in Physics World, 5 Sep 2013

Quantum cryptography is the most secure method of communication available – but it is also expensive, because each pair of users requires its own set of specialized equipment. That could soon change, however, now that physicists working at Toshiba have developed technology to allow up to 64 users to share the same transmission line.

In conventional cryptography one person, Alice, wants to send another person, Bob, an encrypted message. To do so she first sends him a “key” so that the message can be decrypted. But transmitting the key is a security hazard: an eavesdropper, Eve, could easily intercept it, read it and send it on, without Alice and Bob’s ever noticing. […]

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Quantum Cryptography Is Safe Again

ScienceJon Cartwright

Published in Science, 29 Aug 2013

In theory, so-called quantum cryptography provides a totally secure way of sending information. In practice, maybe not. But now physicists have demonstrated how to close a technological loophole that could have left secrets open to eavesdroppers.

Suppose Alice wants to send Bob a secret message. In ordinary cryptography, she can convert the message to binary numbers—i.e., a string of 0s and 1s—and then scramble it by combining it mathematically with another string of random 0s and 1s, which serves as the key. Bob then uses this key to undo the scrambling and read the message. Of course, to make the scheme work, Alice must pass the key to Bob without letting it be intercepted by an eavesdropper, Eve. […]

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