Quantum computing forges ahead

08/03/2012

Updating Magic Universe

So what’s a Majorana fermion then?

A news item in today’s Nature reminds me that last week it was all happening with quantum computing at a meeting of the American Physical Society. IBM announced a breakthrough in the technology, predicting practical computers of unimaginable power within 10 or 15 years. And in Nature Eugenie Samuel Reich discusses what seems to be a discovery of cosmic importance by a team in Delft, announced at the APS meeting. I’ll sum up two strands of progress in a brief update.

In Magic Universe the last section of the story called “BITS AND QUBITS: the digital world and its quantum shadow looming” reads so far:

Towards quantum computers

For a second revolution in information technology, the experts looked to the spooky behaviour of electrons and atoms known in quantum theory. By 2002 physicists in Australia had made the equivalent of Shannon’s relays of 65 years earlier, but now the switches offered not binary bits, but qubits, pronounced cue-bits. They raised hopes that the first quantum computers might be operating before the first decade of the new century was out.

   Whereas electric relays, and their electronic successors in microchips, provide the simple on/off, true/false, 1/0 options expressed as bits of information, the qubits in the corresponding quantum devices will have many possible states. In theory it is possible to make an extremely fast computer by exploiting ambiguities that are present all the time, in quantum theory.

   If you’re not sure whether an electron in an atom is in one possible energy state, or in the next higher energy state permitted by the physical laws, then it can be considered to be both states at once. In computing terms it represents both 1 and 0 at the same time. Two such ambiguities give you four numbers, 00, 01, 10 and 11, which are the binary-number equivalents of good old 0, 1, 2 and 3. Three ambiguities give eight numbers, and so on, until with fifty you have a million billion numbers represented simultaneously in the quantum computer. In theory the machine can compute with all of them at the same time.

   Such quantum spookiness spooks the spooks. The world’s secret services are still engaged in the centuries-old contest between code-makers and code-breakers. There are new concepts called quantum one-time pads for a supposedly unbreakable cipher, but some experts suspect that a powerful enough quantum computer could crack anything. Who knows what developments may be going on behind the scenes, like the secret work on digital computing by Alan Turing at Bletchley Park in England during the Second World War?

   The Australians were up-front about their intentions. They simply wanted to beat the rest of the world in developing a practical machine, for the sake of the commercial payoff it would bring. The Centre for Quantum Computer Technology was founded in January 2000, with federal funding, and with participating teams in the Universities of New South Wales, Queensland and Melbourne.

   The striking thing was the confidence of project members about what they were attempting. A widespread opinion at the start of the 20th Century held that quantum computing was beyond practical reach for the time being. It was seen as requiring exquisite delicacy in construction and operation, with the ever-present danger that the slightest external interference or mismanagement could cause the whole multiply parallel computation to cave in, like a mistimed soufflé.

   The qubit switches developed in Australia consist of phosphorus atoms implanted in silicon using a high-energy beam aimed with high precision. Phosphorus atoms can sustain a particular state of charge for longer than most atoms, thereby reducing the risk of the soufflé effect. A pair of phosphorus atoms, together with a transistor for reading out their state, constitutes one qubit. Unveiling the first example at a meeting in London, Robert Clark of New South Wales said, ‘This was thought to be impossible just a few years ago.’

Update March 2012 – subject to confirmation of the Majorana fermion

Ten years later, when many others had joined in a prolonged experimental quest for quantum computing, IBM researchers at Yorktown Height s claimed to be within sight of a practical device within 10 or 15 years. Dogging all the experimenters was a problem called decoherence  – would the qbits survive long enough to be checked for possible errors?

In 2012 Matthias Steffen of IBM told a reporter, “In 1999, coherence times were about 1 nanosecond.  Last year, coherence times were achieved for as long as 1 to 4 microseconds. With [our] new techniques, we’ve achieved coherence times of 10 to 100 microseconds. We need to improve that by a factor of 10 to 100 before we’re at the threshold [where] we want to be. But considering that in the past ten years we’ve increased coherence times by a factor of 10,000, I’m not scared.”

Then it would be a matter of scaling up from devices handling one or two qbits to an array with, say, 250 qubits., That would contain more ordinary bits of information than there are atoms in the entire universe and it would be capable of performing millions of computations simultaneously. No existing code could withstand its probing, which probably explains why the US Army funded IBM’s work.

Ettore Majorana - CERN image

A by-product of quantum computing research was the discovery of a new particle in the cosmos. In 1937  the Italian physicist Ettore Majorana adapted a theory by the British Paul Dirac to predict a particle that is its own antiparticle – a very strange item indeed! It would be electrically neutral and exhibit peculiar behaviour.

A team led by Leo Kouwenhoven at Delft University of Technology in the Netherland, tested experimentally a suggestion from 2010 about how to create a pair of these particles. At a very low temperature and in a magnetic field, you touch a superconductor with an extremely fine semiconducting wire. As the signature of the presence of “Majorana fermions”, confirmed by the experimental team, the resistance in the wire becomes very low at zero voltage.

The Majorana particle opened a new route to quantum computing, because of its special ability to remember if it swaps places with a sibling. It was expected to be particularly resistant to the decoherence that plagued other techniques. So the Delft discovery promised a new research industry.

References

Steffen quoted by Alex Knapp in Forbes 28 February 2012 http://www.forbes.com/sites/alexknapp/2012/02/28/ibm-paves-the-way-towards-scalable-quantum-computing/

IBM Press Release 28 February 2012 http://www-03.ibm.com/press/us/en/pressrelease/36901.wss

Nature News 8 March 2012: http://www.nature.com/news/a-solid-case-for-majorana-fermions-1.10174

Nature News 28 Feb 2012 http://www.nature.com/news/quest-for-quirky-quantum-particles-may-have-struck-gold-1.10124

“A suggestion from 2010”: paper by Lutchyn et al. in PRL available at arXiv:1002.4033v2


Dying comets probe the Sun

22/01/2012

Updating Magic Universe

Debris traces the solar magnetic field

What started as a bonanza for comet spotters becomes a new tool for exploring levels in the Sun’s atmosphere that have been hard to see up to now. The SOHO spacecraft (Solar and Heliospheric Observatory) has identified more than 1400 small “sungrazing” comets that fly close to the Sun and evaporate. In July last year, the comet observers using SOHO’s Large Angle and Spectrometric Coronagraph (LASCO) team alerted colleagues operating the newer SDO (Solar Dynamics Observatory) to a larger-than-usual sungrazer heading for its doom.

As he reports in the current issue of Science magazine, Karel Schrijver from the Lockheed Martin Advanced Technology Center in California tracked Comet 2011 N3 SOHO by extreme ultraviolet light with his Atmospheric Imaging Assembly on SDO, which observes highly ionized atoms. What he learned about the comet and about the Sun I’ll tell below as a concise update for Magic Universe. Meanwhile the word is that SDO also observed Comet Lovejoy last month, when it survived a close encounter with the Sun, passing behind it and reappearing on the other side.

Here are a few relevant paragraphs from my story about Comets and Asteroids in Magic Universe.

The big comet count came from another instrument on SOHO, called LASCO, developed under US leadership. Masking the direct rays of the Sun, it kept a constant watch on a huge volume of space around it, looking out primarily for solar eruptions. But it also saw comets when they crossed the Earth-Sun line, or flew very close to the Sun.

A charming feature of the SOHO comet watch was that amateur astronomers all around the world could discover new comets, not by shivering all night in their gardens but by checking the latest images from LASCO. These were freely available on the Internet. And there were hundreds to be found, most of them small ‘sungrazing’ comets, all coming from the same direction. They perished in encounters with the solar atmosphere, but they were related to larger objects on similar orbits that did survive, including the Great September Comet (1882) and Comet Ikeya-Seki (1965).

SOHO is seeing fragments from the gradual break-up of a great comet, perhaps the one that the Greek astronomer Ephorus saw in 372 BC,’ explained Brian Marsden of the Center for Astrophysics in Cambridge, Massachusetts. ‘Ephorus reported that the comet split in two. This fits with my calculation that two comets on similar orbits revisited the Sun around AD 1100. They split again and again, producing the sungrazer family, all still coming from the same direction.’

The progenitor of the sungrazers must have been enormous, perhaps 100 kilometres in diameter or a thousand times more massive than Halley’s Comet. Not an object you’d want the Earth to tangle with. Yet its most numerous offspring, the SOHO-LASCO comets, are estimated to be typically only about 10 metres in diameter.

Update January 2012

In July 2011 a larger than usual sungrazer spotted by SOHO was tracked across the face of the Sun by a newer spacecraft, the Solar Dynamics Observatory, SDO. Named as Comet 2011 N3 SOHO, it evaporated to the point of invisibility after 20 minutes, but not before the event had transformed the game from comet-spotting fun to highly productive cometary and solar physics.

Led by Karel Schrijver from the Lockheed Martin Advanced Technology Center in California, the SDO team was able to gauge the size of the comet. Initially it was up to 50 metres wide. This opened the way to investigating the sungrazers in much more detail. It should become possible to learn more about the composition of these comets, according to how they boil and rupture in the intense heat.

As for solar physics, the miniature tail of the dying comet lit up magnetic field lines at altitudes high in the solar atmosphere that otherwise are almost impossible to detect. Seeing the lines traced by sungrazers at different heights above the Sun will make it possible to trace more accurately the links between the magnetism near the visible surface and the vast field that reaches out into space and influences the Earth.

References

Karel Schrijver et al., Science 20 January 2012, vol. 335, pp. 324-328 DOI: 10.1126/science.1211688

NB: Movies are available at http://www.sciencemag.org/content/335/6066/324/suppl/


With graphene, carbon scores again

05/10/2010

Updating Magic Universe

With graphene, magical carbon scores again

Today’s award of the physics Nobel Prize to Andre Geim and Konstantin Novoselov “for groundbreaking experiments regarding the two-dimensional material graphene” gives me the chance to update what I wrote about carbon honeycombs in Magic Universe, which was published a year before the graphene story broke in 2004.

In an earlier post I’ve rhapsodised about polycyclic aromatic hydrocarbons in the cosmos, and their relevance to the origin of life – see http://calderup.wordpress.com/2010/06/01/comets-and-life-2-2/ — but now it’s the terrestrial side of the carbon saga that makes the mind boggle. We’re talking about the familiar graphite that comes off the end of your pencil when you write, but now reduced to a layer just one atom thick.

The relevant story in Magic Universe is called “Buckyballs and nanotubes: doing very much more with very much less.” Starting with a nod to the geodesic dome designer Buckminster Fuller, who inspired the names of the football-like C60 molecules, fullerenes or buckyballs, found in 1985, it proceeds from that discovery to the molecular basket-work of the carbon nanotubes, first made in 1991. Today’s update belongs after some cheerful speculations that followed.

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Relativity on the human scale

24/09/2010

Updating Einstein’s Universe and Magic Universe

Relativity on the human scale

The most gratifying physics I’ve seen for a while comes in today’s Science magazine, from James Chin-Wen Chou and his colleagues in the Time and Frequency Division at the National Institute of Standards and Technology in Boulder, Colorado. They detect well-known effects of relativity on the rate of time passing, but now on the scale of ordinary human activities.

Standard atomic clocks employ microwaves to ensure their regularity, but Chou’s team used laser light in a pair of aluminium-27 optical clocks (invented in 2005), which gives about 100 times better accuracy. In one experiment, they used an electric field to jiggle the aluminium ion at the heart of a clock and showed that time passed more slowly in accordance Einstein’s Special Relativity theory, about the effect of motion on time. The effect of atomic motion as slow as 8 metres per second (about 30 km/h) was detectable.

Raising a clock makes it run a little faster. Credit: Chou et al., Science, 24 September 2010 – see reference.

Especially pleasing for me was another experiment, in which one clock was jacked up just 33 cm relative to the other. The clock gaining height ran faster because it was further from the Earth’s centre of gravity, and the gravitational field was slightly weaker, in accordance with General Relativity. As the change in clock rate was only about 40 parts in a billion billion (1018), its detection was a tour de force for the NIST team.

This effect of altitude on time was the key to the efforts by Martin Freeth of BBC-TV and me to make Einstein’s theory of gravity, General Relativity, comprehensible to the public, in our film “Einstein’s Universe” (1979).

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Wheat genome

27/08/2010

Updating Magic Universe

The genetic code of wheat

Last night the UK’s Biotechnology and Biological Sciences Research Council made available online a draft of the largest genetic code of an organism ever tackled – the genome of wheat, which is five times larger than the human genome and more than 30 times larger than that of rice, revealed back in 2002. But well worth the effort, for a crop with virtues that have shaped human history since its domestication more than 10,000 years ago.

Spikelet of Chinese Spring wheat, Triticum aestivum. Photo: E.J.M. Kirby

Chinese Spring wheat is the variety now read. Leading the work is the British team of Neil Hall and Anthony Hall at the University of Liverpool, Keith Edwards and Gary Barker at the University of Bristol. and Mike Bevan at the John Innes Centre. Most of the actual gene-reading was done with a “platform” developed in the USA by a subsidiary of Swiss company Roche.

The implications are big. Although the genome isn’t yet organised into its chromosomes, plant breeders now have access to 95 per cent of all wheat genes. That should shorten by some years the time required to develop viable new varieties of wheat that can thrive in marginal conditions – adapted for example to face drought, salty soil, or disease.

Here’s the most relevant extract from the story in Magic Universe called “Cereals: genetic boosts for the most cosseted inhabitants of the planet.”

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Dark matter’s lens

20/08/2010

Updating Magic Universe

Dark matter’s lens on the cosmic scenery

Since 1996 the efforts of the French astrophysicist Jean-Paul Kneib to exploit natural lenses in the sky, created by the dark matter that surrounds clusters of galaxies, have fascinated me. While other stargazers used the “gravitational lenses”, bending light in the Einsteinian manner, to see galaxies far beyond the range of unaided telescopes, Kneib’s aim was to chart the mysterious dark matter itself. He wanted to see how visible matter and the far weightier dark matter have interacted through cosmic time – to see “the whole history of the Universe from start to finish”, as Kneib remarked to me in 2002.

It’s been taxing work, but now Kneib is one of the team reporting in today’s Science magazine about the dark matter around one the richest known clusters of galaxies. Abell 1689 lies 2.2 billion light-years away in the Virgo constellation, and a couple of years ago its extraordinary lensing power revealed a very distant and early object in the sky, Galaxy A1689-zD1, 12.8 billion light-years away. But that’s by the way

The new report not only gauges the cluster’s dark matter but uses the galaxies beyond it to infer the overall nature of space-time itself, dominated by the even more massive dark energy that drives the accelerating expansion of the Universe.

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superatomic circus

18/08/2010

Pick of the pics and Updating Einstein’s Universe & Magic Universe

Seeing the superatomic circus

When ultra-cold rubidium atoms club together in the superatoms called Bose-Einstein condensates, they usually make untidy crowds, as on the left. But a team led by Stefan Kuhr and Immanuel Bloch at the Max-Planck-Institut für Quantenoptik in Garching, Germany, brings them to order in a neater pattern, as seen in the middle picture. With more rubidium atoms the superatom grows wider (right). Criss-cross laser beams create a lattice-like pattern of pools of light where the atoms like to congregate. When the laser light’s electric field is relatively weak, the atoms jump (by quantum tunnelling) from one pool to another, creating the usual disorder. A stronger field, as in the central and right-hand images, fixes them in the novel state of matter called a Mott insulator. But atoms can be lost from the condensate, which explains the ring-like appearance on the right. Images from MPQ.

[You're recommended to click on the images for a better view]

Single atoms are located at the sites indicated by circles. Fig. 3 in Nature paper, Sherson et al. see ref.

What’s new here, in an advance online publication in Nature,  is not the creation of these kinds of  superatoms but the German team’s success in imaging them, with a specially developed microscope that picks up fluorescence from the atoms caused by the cooling process. In the image on the right individual atoms are pinpointed.

It’s exciting stuff, because we’re probably seeing the dawn of a new technology – after electronics comes “atomics”. If individual atoms in a superatom can be manipulated, they might be used to carry “addressable” information in an atomic computer.

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