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Home » Page 1484

Quantum effect spotted in a visible object

Physicists in California have observed true quantum behaviour in a macroscopic object big enough to be seen with the naked eye. This is the first time this feat has been achieved and it could shed light on the mysterious boundaries between the classical and quantum worlds.

One of the fundamental principles of quantum mechanics is that objects can be in two states at the same time. This means that an electron can, for instance, be in two places at once. However, these “superposition” states are never seen in classical, macroscopic objects – one example being Schrödinger’s famous cat, who clearly could not be both dead and alive. Until now, such states have only been observed in atomic-scale objects and some larger molecules, such as a “buckyball”, which is made up of 60 carbon atoms.

Scientists have long wanted to demonstrate superposition in larger objects but a significant challenge here is to eliminate all thermal vibrations in the object, which mask or destroy quantum effects. To achieve this, the object needs to be cooled down to its quantum ground state – at which point the amplitude of vibrations reduces to close to zero.

A quantum drum

Andrew Cleland and colleagues of the University of California, Santa Barbara, have now achieved this for a substantially larger object than in previously experiments – an object so large in fact that it can just about be seen with the naked eye. The object is a mechanical resonator made of aluminium and aluminium nitride, measuring about 40 µm in length and consisting of around a trillion atoms. It is a thin disc, which resonates at about six billion vibrations per second.

In the experiment, Cleland’s team reduce the amplitude of the vibrations in the resonator by cooling it down to below 0.1 K. The high frequency of the aluminium resonator was key to the experiment’s success, because the temperature to which an object needs to be cooled in order to reach its ground state is proportional to its frequency. “A regular tuning fork, for example [with significantly lower frequency], would need to be cooled by another factor of a million to reach the same state,” Cleland said.

Next, the team measured the quantum state of the resonator by connecting it electrically to a superconducting quantum bit or “qubit”. The qubit acts, in fact, like a “quantum thermometer” that can identify just one quantum thermal excitation, or phonon. Once this has been done, the qubit can then be used to excite a single phonon in the resonator. This excitation can be transferred many times between the resonator and qubit.

Dead and alive, at once

In this way the researchers created a superposition state of the resonator where they simultaneously had an excitation in the resonator and no excitation in the resonator, such that when they measured it, the resonator has to “choose” which state it is in. “This is analogous to Schrödinger’s cat being dead and alive at the same time,” says Cleland.

“Unlike other measuring instruments, [the qubit] allowed us to measure the mechanical resonator while preserving all quantum effects,” Cleland told physicsworld.com. “Most measuring instruments disturb the mechanical object by heating it up, and so destroy the very quantum effects being sought.”

The experiments could have important implications for new quantum technologies, like quantum information processing, and for investigating the boundaries between the quantum and classical worlds – one of the least understood areas in physics.

“Another long-term prospect is testing the foundations of quantum physics,” writes Markus Aspelmeyer of the University of Vienna in a commentary in Nature. “For example, superposition states of massive objects may be used to test possible deviations from quantum mechanics, which have been suggested to eliminate the Schrödinger’s cat paradox.”

This research is published in Nature.

A radon detector for earthquake prediction

Recent events in Haiti and Chile remind us of the devastation that can be wrought by an earthquake, especially when it strikes without warning. For centuries, people living in seismically active regions have reported a number of strange occurrences immediately prior to a quake, including unexpected weather phenomena and even unusual behaviour among animals. In more recent times, some scientists have suggested other precursors, such as sporadic bursts of electromagnetic radiation from the fault zone. Unfortunately, none of these suggestions has led to a robust, scientific method for earthquake prediction.

Now, however, a group of physicists, led by physics Nobel laureate Georges Charpak, has developed a new detector that could measure one of the more testable earthquake precursors – the suggestion that radon gas is released from fault zones prior to earth slipping.

Spewing from the Earth’s guts

In the last decade, several studies have concluded that elevated concentrations of radon gas in soil or groundwater could be the sign of an imminent earthquake. It is believed that the radon is released from cavities and cracks as the Earth’s crust is strained prior to the sudden slip of an earthquake. In order to test this hypothesis, however, researchers would need to deploy several hundred detector devices along a fault zone. Although several commercial devices could, in theory, perform this task, these devices are too expensive for large-scale application. In addition, it is not clear whether many of these devices would still work in the presence of water.

Charpak’s alternative detector is based on established technology already in action in extreme conditions at laboratories such as CERN. It consists of a wire-type counter, which is the concept for which Charpak won his Nobel prize in 1992. In these devices, particles such as radon enter a gas-filled container and ionize some of the gas particles. The resulting ions and electrons are accelerated by a potential on the wire, causing a cascade of ionization that results in a current in the wire.

One key feature of this new detector design is that it works with ambient air, thus avoiding the need to keep refilling the detector’s ionization chamber with a particular gas. It also has a high efficiency, which was achieved by including multiple wires in the ionization chamber. In laboratory tests, the researchers report a radon count of 140 Bq.m–3 over one minute, which is comparable to that offered by commercial devices. The tests also show that the device still functions in 70% humidity, while single-wire detectors start to falter at just 30% (arXiv: 1002.4732v1).

Detecting success

“The instrument they propose is based on a very old and very well established detector technology,” says Ariella Cattai, a detector physicist at CERN. “What is very original with this work is the way they want to operate these detectors – in simple air and not in a complicated gas mixture like we normally use.”

Paulo Fonte, director of the Instrumentation Laboratory of Portugal (LIP), agrees that in using the ionization of air the researchers have “broken a taboo” in detection, and he does not foresee any major hurdles in developing this proto device into a commercially viable detector. “It detects alpha particles, which is all that is needed to detect heavy radioactive contaminants. I don’t know how well [this research] is funded, but even if the chances of succeeding are slim, the prize would be so important that it is for sure worth investigating.”

A member of Charpak’s team, Vladimir Peskov, who works at the National Autonomous University of Mexico, says that the group’s next step is to run more tests and develop a way of networking the detectors along a fault zone. They will also investigate ways of monitoring radon levels in groundwater.

Take me out to the (digitized) ball game

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Nathan’s results table

By Hamish Johnston in Portland, Oregon

Although college basketball’s “March madness” is about to start, it’s the physics of baseball that people are talking about here at the APS March Meeting.

Alan Nathan of the University of Illinois at Urbana Champaign spoke about his analysis of data from the PITCHf/x and HITf/x systems that have been installed in all major-league ballparks by Sport Vision.

These systems track the speed and trajectory of the ball allowing, for example, digital reconstructions of plays for television viewers.

It turns out that all of these data are available to the public – and Nathan has used them to study the flight of the baseball.

One question he addressed is the widely held belief that hit balls travel further in the new Yankee Stadium in New York than in other ballparks.

Nathan defined the “carry” of a hit as the distance the ball actually travelled divided by the distance the ball would have travelled (given its velocity when hit) in a vacuum.

You can see the results above, and there is nothing special about the new Yankee Stadium – denoted “NYC-A” – indeed its carry is a little below average (the red line).

So what’s the story with Denver?

Here’s a hint – Denver’s Colorado Rockies used to play in Mile High Stadium.

John Updike meets The Sopranos

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Nan Haemer sings Updike

By Hamish Johnston in Portland, Oregon

My fondest memory of the 2010 APS March Meeting will be the soprano Nan Haemer’s performance of Updike’s Science – music by the physicist Brian Holmes and words by the late John Updike.

Brian is at the left of the photograph above, turning pages for Terry Nelson on the piano.

As well as being a condensed matter physicist at San Jose State University, Holmes is a professional French horn player and a composer.

Updike’s Science consists of musical settings of six poems by John Updike. Some of the poems make direct reference to science – “Cosmic gall”, for example, begins:

“Neutrinos they are very small…”

Other poems are included because they remind Holmes of science – “Lament for cocoa”, for example could be a lament for thermodynamics with the lines:

“The scum has come, My cocoa’s cold”

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Holmes blowing his horn

Before the performance Holmes entertained the crowd with a lively demonstration of the physics of brass instruments.

What did I learn? Well it seems that the pitch of a trumpet with a bell is higher than a similar instrument that ends in a plain tube. Although Holmes didn’t say so, the logical conclusion is that the bigger the bell the higher the pitch – but I would have thought bigger bells result in lower pitches.

The reason, I think, is that a larger bell means that the acoustic node of the instrument is further into the trumpet – which shortens the wavelength of the sound, boosting the pitch.

Top South African astronomer reinstated

One of South Africa’s top astronomers, Phil Charles, has been reinstated as director of the South African Astronomical Observatory (SAAO) having been cleared of sharing confidential information with “outsiders”. Charles had been suspended last month by the National Research Foundation (NRF) of South Africa for “leaking” parts of “confidential foundation documents”.

Physicsworld.com has learned that these documents concerned plans to restructure the management of national facilities such as the SAAO, and plans for the site of the operations centre for the forthcoming MeerKAT radio telescope.

On 12th March, however, an independent hearing found Charles not guilty of the charges, because the “outsiders” – who turned out to be senior South African and US astronomers – had a right to know. Sources close to Charles say that the matter began in December with an e-mail to him from the vice-president of the NRF, Gatsha Mazithulela.

In the e-mail – which apparently was not marked confidential – Mazithulela detailed the restructuring of national facilities and the newly selected site of the operations centre of MeerKAT, which is currently being built in South Africa as a prototype of the Square Kilometer Array (SKA). SKA, which will be built in either Australia or South Africa, will combine the signals from thousands of small antennae spread over a distance of more than 3000 km to make a radio telescope capable of extremely high sensitivity and angular resolution.

‘Immense damage’

Recognizing that the information had consequences for the facilities and for local university astronomers, Charles shared it with other senior colleagues in the hope that a formal announcement could be delayed until the astronomical community had had a chance to discuss the matter. These senior colleagues included astronomers at the University of Cape Town and Ted Williams, the US astrophysicist who chairs the board governing the SAAO’s SALT telescope.

“It was clear with the MeerKAT centre that immediate action was required to avoid embarrassment to the minister [of science and technology] if the choice of site was disputed after the announcement, which was quite likely as it appeared that no astronomers had been consulted,” says one of Charles’s close colleagues who did not want to be named.

Another colleague says that the NRF’s “head-in-the-sand attitude” had caused “immense damage” to South Africa’s scientific reputation. “Had this been handled in an open and consultative manner, instead of adopting a secretive and intimidating approach, all of this could easily have been avoided,” he says. Charles could not be reached for comment.

Still ongoing

Phil Charles
Phil Charles

However, it appears as though the matter may still not be settled. Patrick Thompson, group executive of stakeholder relations at the NRF, said in a written statement: “The NRF believes that the issues that gave rise to these proceedings may still exist and that they still require [to] be dealt with. Be that as it may, the NRF accepts the verdict of the independent chair, and will therefore not contest its final conclusion.”

Yesterday the Royal Society of South Africa issued a statement criticizing the NRF’s actions. “The major charge [Charles] faced was that he had shared ‘secret information’ with colleagues regarding decisions the NRF had taken in connection with the future of astronomical facilities in South Africa,” it read. “However, this was information that these very colleagues should have been given by the NRF and indeed, because they are stakeholders, they should also have been party to the process that led to these decisions.”

“The action taken against Prof. Charles has disturbed the international scientific community and placed a grave question mark against South Africa’s international scientific reputation,” it adds. “Corporate governance would appear to be lacking and clear policy direction ignored.”

Heads in the clouds

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Fluffy simulations

By Hamish Johnston in Portland, Oregon

Have you ever wondered why clouds are fluffy?

Well, it’s not an easy question – according to Yong Wang at UCLA. Wang was here at the APS March Meeting to talk about his simulations of cumulus clouds, the fluffy ones that tend to appear after about noon on a sunny day and don’t tend to spoil the rest of the day.

Wang says that these clouds are droplets supported by thermal convection, and their shapes arise because this is a “complex non-linear system” that is driven by thermal plumes.

The simulation begins with a homogeneous layer of water droplets into which small thermal plumes rise. After a while, the jostled droplets look a lot like fluffy cumulus clouds (see above).

Wang didn’t seem to think that there were any practical applications for his work – but I would have thought this could help climate physicists understand why certain clouds form.

You can read more about Wang’s simulations here.

What is the most powerful accelerator in the world?

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Record breaking accelerator

By Hamish Johnston in Portland, Oregon

Here’s a question for you, what is the most powerful accelerator in the world?

No, it’s not the LHC – that holds the record for energy – the answer is the Spallation Neutron Source (SNS) at the Oak National Lab in Tennessee.

In September 2009 the facility delivered a pulsed beam of 1 GeV protons at a power of 1 MW.

The pulses are fired at a target of liquid mercury, creating copious amounts of neutrons, which can then be slowed down and used for studying solids and liquids.

This afternoon I saw a nice talk by Stuart Henderson of Oak Ridge about recent progress at the SNS. Since experiments began in 2006, the number of instruments attached to the neutron beamline has grown to 12 and he expects that 16 instruments will be running by 2012.

And of course, Oak Ridge hope to upgrade the facility between 2012–2017 – boosting the energy to 1.3 GeV and the power to 3 MW.

Is your hair dusty?

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Rising plumes

By Hamish Johnston in Portland, Oregon

Any guesses as to what you are looking at?

The red shape is a “person” sitting in a small room. The temperature at the surface of the person is 25 degrees – the temperature of your clothes, apparently – and the temperature of the room is 20 degrees.

The image is from a huge simulation of how air circulates in a room with floor and ceiling vents that was done by John McLaughlin and colleagues at Clarkson University.

The yellow plumes are warm air rising from the sitting person – and McLaughlin looked at how tiny particles comparable to viruses or pollen behaved in the room. He found that the plumes tend to concentrate the particles over the person’s head – and then they fall down onto the poor person!

This could be bad news in a hospital, for example, where there could be lots of nasty bugs floating around.

So if your head is getting dusty, perhaps it’s because you are sitting perfectly still in a small room.

Graphene – it's still hot

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Packed house for Andre Geim

By Hamish Johnston in Portland, Oregon

I had to push my way through the crowd here at the APS March Meeting just to stand at the back of Andre Geim’s talk called “Graphene update”. It seems that there is a still a lot of interest in the wonder material – sheets of carbon just one atom thick – that promises to revolutionize electronics.

The University of Manchester-based graphene guru spoke about a half-dozen or so open questions in the field.

Is graphene ferromagnetic at room temperature, as some have claimed?

“No,” says Geim, who explained how he and his colleagues found no evidence for ferromagnetism down to a chilly 2K.

And what about the vexing question of how to create a bandgap in gapless graphene so that it can be used to create conventional semiconductor devices?

Straining graphene by up to 10% hasn’t worked – and recent calculations suggest that you would have to have to strain the stuff by as much as 25% before a gap appears.

One way forward, according to Geim, is to somehow apply just the right amount of “non-uniform” strain to the material. While this appears to work in theory, it requires the strain to vary on length scales of about a micron – which physicists can’t do today.

A gap could also be introduced by altering the chemistry of graphene. Geim and colleagues have already hydrogenated graphene to create graphane – which has a gap. However, Geim says the material is “unstable” and not suitable for making semiconductor devices.

So if hydrogen doesn’t work, why not try fluorine to create fluorographene? That’s what Geim and colleagues have done – and although the result was a semiconductor with a great deal of disorder, he said that fluorographene could be the way forward to a gap.

Perhaps the most intriguing topic touched on by Geim is the fabrication of “quantum capacitors”, which comprise one graphene plate and one metal plate. In such a device the capacitance is a function of the applied voltage, dipping to zero at zero voltage. And the capacitance oscillates if a magnetic field is applied. I’m not sure what you could do with such a device – but it’s yet another example of the wonders of graphene.

Two quantum channels are very different than one

By Hamish Johnston in Portland, Oregon

I know it’s a cliché, but the quantum world gets weirder the more you learn about how it works.

Yesterday I went to a talk by Graeme Smith of IBM Research, whose talk was entitled “Surprises in the theory of quantum communications”.

The surprise that Smith focused on is that two transmission channels – both of which are too noisy or lossy to transmit quantum information individually – can somehow join forces to create a very good channel for transmitting quantum information.

A classical transmission channel fails if you put a signal in one end and get nothing (or just noise) out the other end. By contrast, a quantum channel can fail if you input quantum information but its quantum nature is lost when it gets to the other end – information is transferred, but not quantum information.

But according to Smith, it’s possible that each channel is capable of transmitting a certain subset of the quantum information – but not all of it. The trick is to have two or more channels combine their quantum strengths to overcome their weaknesses.

“The weakness of one is made up for by the strength of the other,” explained Smith.

While it sounds like a great way to build a robust transmission channel from a bunch of bad connections, Smith said that it is not currently clear how to decide which bad channels can be grouped together to create a good channel.

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