Single-atom gates open the door to quantum computing

Published in Physics World, 11 Apr 2014

A quantum-information analogue of the transistor has been unveiled by two independent groups in Germany and the US. Both devices comprise a single atom that can switch the quantum state of a single photon. The results are a major step towards the development of practical quantum computers.

Unlike conventional computers, which store bits of information in definite values of 0 or 1, quantum computers store information in qubits, which are a superposition of both values. When qubits are entangled, any change in one immediately affects changes in the others. Qubits can therefore work in unison to solve certain complex problems much faster than their classical counterparts. […]

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Zombie universe

Published in New Scientist, 29 Mar 2014

AS ENDINGS go, it is a bit of an anticlimax. As the universe enters old age, its stars burn out. Slowly, the temperature across the cosmos reaches equilibrium. With no heat flowing, thermodynamic laws make it impossible to transfer energy in a useful way. Nothing interesting or productive happens any more. Everything creaks to a standstill.

This “heat death” of the universe was a favoured topic of the gloomier sort of 19th-century physicist. These days, we console ourselves that, if it is to happen, it will not be for many, many multiples of the current age of the universe.

Antony Valentini, a theoretical physicist at Clemson University in South Carolina, is less sanguine. For the past two decades, he has championed the idea that something like heat death has already happened – not in our layer of reality, admittedly, but on an underlying level that we are hard-pressed to see.

Fundamental physics is not short of eccentric and unworkable proposals, and it is easy to dismiss such a bold suggestion. But there are aspects of Valentini’s idea that make some of his peers believe he might just be on to something. Just as a thermodynamic heat death would prevent us from doing anything useful with energy in the distant future, if Valentini’s “quantum death” has happened, it could explain our puzzling inability to fully get to grips some of aspects of nature – those to do with quantum behaviour. “He’s well respected and taken seriously,” says Carlo Rovelli of Aix-Marseille University in France.

Now Valentini thinks he may have seen the first evidence for this theory, etched in the afterglow of the big bang. Strange as it might seem, quantum death might breathe new life into our understanding of reality. […]

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Computer memory made from sugar cube

Published in Chemistry World, 19 Mar 2014

A sugar cube that functions as computer memory has been created by scientists in the US. The sugar-based metal–organic framework infused with rubidium hydroxide can be switched between high and low resistance states, in a similar way to resistive random-access memory (RRAM).

Metal–organic frameworks (MOFs) are made from organic molecules held in a 3D lattice by metal ions or clusters. Typically porous, they are widely investigated for storing gases, such as hydrogen for fuel. But Bartosz Grzybowski and colleagues at Northwestern University in Evanston, Illinois, have been investigating MOFs for storing something entirely different: information. […]

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Thermobrachytherapy: two treatments in one

Published in MPW, 17 Mar 2014

A seed that can be implanted inside a tumour to deliver both heat and radiation simultaneously has been developed by scientists in the US. The seed, which has not yet been tested on actual tumours, is expected to be more effective than other forms of thermoradiotherapy in treating cancer. […]

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Organic circuits – lighter, cheaper and bendier

Published in Horizon, 17 Mar 2014

A new type of plastic electronics made from organic materials is lighter, cheaper, and more flexible than any of today’s technology. Such circuits could be worn on clothing or placed inside medical sensors.

Electronic components such as transistors form the backbone of all modern computers, whether they are laptops, tablets, or smartphones. Today they are almost exclusively made from silicon, a widely available semiconductor.

But silicon has its drawbacks: it is opaque, almost always rigid, and has to be manufactured in individual sheets. If electronics could instead be made from organic materials – those such as plastic that contain chains of carbon atoms – it could be transparent, physically flexible, and fabricated continuously on a roll. […]

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Computing in the classroom

Published in Physics World, 1 Mar 2014

Computer science is essential for modern physics, yet students come little prepared for it. That may soon change, says Jon Cartwright

Particle physics 40 years ago was a slow process. Collisions had to be recorded on black-and-white photographs, which were then pored over by hundreds of technical assistants. This was true even of (for the time) cutting-edge accelerators such as CERN’s Big European Bubble Chamber, which took images every three seconds.

Today it is a very different story. Inside the Large Hadron Collider (LHC) at CERN, for instance, collisions occur every 25 nanoseconds. Data generated at such rates have to be processed by a network of powerful computers around the world. But particle physics is far from being the only field within physics that makes use of high-level computing. From simulating the behaviour of cold atoms to designing control systems for complex equipment, computing has become not an optional but a necessary activity. […]

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Small-animal irradiation: dose comparisons

Published in MPW, 12 Feb 2014

Certain types of conformal small-animal radiotherapy systems can give higher radiation doses to critical organs if the target tumours are deep-seated, a US-based study has found. Although the study also found that all conformal systems are better for small tumours, it suggests that their characteristics ought to be studied further for their full advantage to be taken (Med. Phys.41 011710). […]

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Histotripsy offers selective tissue ablation

Published in MPW, 4 Feb 2014

Histotripsy, a technique in which ultrasound is used to non-invasively remove tissue, was invented about a decade ago. Now, the pioneers of histotripsy have shown that the degree of ablation depends on a tissue’s mechanical properties. The discovery suggests that histotripsy could be used to selectively remove problem tissue around difficult areas, such as major blood vessels (Phys. Med. Biol. 59 253).

The pioneers of histotripsy, Charles Cain and colleagues at the University of Michigan in Ann Arbor, MI, believe that the technique works because pulses of ultrasound in tissue cause rapid cycles of compression and expansion, which in turn form microbubbles. They believe that these microbubbles then collapse, generating bursts of energy that break up the tissue and destroy cells. […]

The rest of this article is available here.

NSA keys into quantum computing

Published in Physics World, 1 Feb 2014

Leaked documents suggest that the US National Security Agency is developing quantum computers to crack cryptography codes, but what progress has the agency really made? Jon Cartwright investigates

The US National Security Agency (NSA) has a classified programme to build a quantum computer that can break modern Internet security, according to documents leaked by the former NSA contractor Edward Snowden. The documents, which were published last month in redacted form by the Washington Post, have surprised few physicists working in the field. However, they have led to speculation about the status of NSA research and a renewed debate on the risks of developing quantum computers.

Quantum computers are devices that rely on quantum phenomena such as superposition, in which a system exists in multiple states at once, and entanglement, in which the states of two systems become inextricably linked. Unlike classical computers, which store bits of information in definite values of 0 or 1, quantum computers store information in quantum bits, or qubits, which are a superposition of both. When qubits are entangled, any change in one immediately effects changes in the others. Qubits can therefore work in unison and solve certain complex problems much faster than their classical counterparts. […]

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The lure of G

Published in Physics World, 1 Feb 2014

For over 200 years physicists have tried to pin down the value of the gravitational constant. Jon Cartwright finds out what’s been taking them so long

It was back in 1982, during his PhD, when Clive Speake first understood the true nature of gravity. “It was amazing,” he recalls fondly. “I remember going out the night I had done the experiment for the first time, and I just looked up at the Moon. It had given me a completely different feel for what the Moon is, you know? Why it’s there.”

Such epiphanies are not uncommon among those who perform measurements of the gravitational constant. Gravity is the most famous of nature’s forces, because it is the one that is most obviously present in our lives. Ever since Isaac Newton was inspired by a falling apple, everyone has known that it is gravity behind the inevitable phrase “what goes up, must come down”. Yet despite our familiarity with gravity, few of us have experienced the force other than when it is directed towards the ground beneath our feet.

To see why, you need only look at the numbers. Gravity is the weakest force – 10^36 times weaker than electromagnetism, the force that governs most other everyday phenomena. The only reason we can feel gravity on Earth is because it scales with mass: our planet’s mass of five zetta-tonnes (5 × 10^21 tonnes) is enough to bring gravity into the realm of normal human perception. But the force still exists between all other objects, and if you do ever witness it with Earth out of the equation – for example, in the faint shift of two suspended metal weights – it might at first seem like magic. “It’s a liberating experience,” says Speake, who is now based at the University of Birmingham in the UK.

Liberating – and infuriating. The gravitational constant – “big G”, as it is commonly known – is what characterizes the strength of gravity according to Newton’s law, and it is fiendishly difficult to measure. Experiments struggle to deliver uncertainties much smaller than one part in ten thousand – compare that, for instance, with the proton–electron mass ratio, which is known to four parts in ten billion.

Low precision alone is enough to keep a metrologist up all night. But in recent years, a much more serious problem has arisen: measurements of big G are in wild disagreement with one another. Since the turn of this century, values recorded by some of the best labs in the world have been spread apart by more than 10 times their estimated uncertainties. Something is amiss – yet no-one is quite sure what. “You go over it, and over it, and over it,” says Speake. “And there comes a time when you say, I just can’t think of anything we’ve done wrong.” […]

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