Electrical control of nuclear spin qubits

Researchers of Karlsruhe Institute of Technology (KIT) and their French partners succeeded in making an important step towards quantum computers. Using a spin cascade in single-molecule magnet, the scientists demonstrated how nuclear spins can be manipulated with electric fields. Electric manipulation allows for a quick and specific switching of quantum bits. The experimental results are now reported in the journal Science .

One of the most ambitious goals of nanotechnology is to realize a quantum computer. Such a computer based on quantum mechanics principles is to solve tasks much more efficiently than a classical computer. While the latter works with bits that assume the value of zero or one, a quantum computer uses so-called quantum bits, briefly referred to as qubits, as smallest computation units. They may also assume values in between. Qubits may rely on nuclear spins, i.e. intrinsic angular momentums of atomic nuclei. They orient relative to a magnetic field in upward (up) or downward (down) direction. Interlinkage of qubits with each other results in mixed quantum states, on the basis of which many calculation steps can be executed in parallel.
To integrate nuclear spin-based qubits into electronic circuits and specifically trigger novel information processes, specific electric manipulation of nuclear spins is required. A team of scientists of the KIT and the Centre National de la Recherche Scientifique (CNRS) in Grenoble and Strasbourg recently succeeded for the first time in manipulating a single nuclear spin in a purely electric manner. "Use of electric instead of magnetic fields paves the way to addressing quantum states in conventional electronic circuits," explains Professor Mario Ruben, Head of the Molecular Materials Research Group of KIT's Institute of Nanotechnology (INT). "There, quantum states can be manipulated specifically by so-called displacement currents. Then, they can be directly read out electronically."
For their experiments, the researchers used a nuclear spin-qubit transistor that consists of a single-molecule magnet connected to three electrodes (source, drain, and gate). The single-molecule magnet is a TbPc2 molecule – a single metal ion of terbium that is enclosed by organic phthalocyanine molecules of carbon, nitrogen, and hydrogen atoms. The gap between the electric field and the spin is bridged by the so-called hyperfine-Stark effect that transforms the electric field into a local magnetic field. This quantum mechanics process can be transferred to all nuclear spin systems and, hence, opens up entirely novel perspectives for integrating quantum effects in nuclear spins into electronic circuits.
Reference :
http://phys.org/news/2014-06-electrical-nuclear-qubits.html

Anyone who thought that Sachithra Senanayake being reported to the ICC for a suspect bowling action might be a cue for Sri Lanka to excuse him from duty, and the added attention it would bring, did not reckon with the player himself. Figures of 1 for 36, including the wicket of England's top-scorer, Alastair Cook, were just one thread of Sri Lanka's series-clinching six-wicket win but, by running out Jos Buttler while the batsman was backing up, Senanayake ensured that the narrative would be wound around him.
Mahela Jayawardene and Lahiru Thirimanne scored half-centuries as Sri Lanka kept cool in an atmosphere that was simultaneously heated and damp. England's bowlers, in particular James Tredwell and James Anderson, managed to ratchet up the asking rate but some business-like thumping from Angelo Mathews, who had to contend with a commentary from the fielding side over his role in Buttler's dismissal, sealed victory and another fortifying series triumph ahead of the Tests.

Mathews had earlier expressed his disappointment over Senanayake's situation - he is required to undergo biometric testing within the next 20 days - but Sri Lanka's capacity for turning adversity in their favour is well known. A comparable incident came during the triangular Carlton & United series in 1999, when Arjuna Ranatunga led his players off at Adelaide Oval after Ross Emerson no-balled Muttiah Muralitharan for throwing. England were again on the losing side, Sri Lanka chasing down a target of 303 with one wicket and two balls to spare.
As then, an offspinner with a controversial action was central to the drama. Having twice stopped in his delivery stride during the 42nd over to warn the batsmen - both Buttler and Chris Jordan - for backing up too far, Senanayake followed through on the threat in the 44th, turning slowly to break the wicket with Buttler a yard or so down the pitch.
The umpires consulted Mathews, Sri Lanka's captain, and he nodded his assent in upholding the appeal. That meant the first instance of 'Mankading' in international cricket since Peter Kirsten's innings was ended by Kapil Dev in such a manner during an ODI between South Africa and India in 1992.
There was predictable hostility from the crowd, even without suspicions over the legality of his bowling, but Senanayake was within his rights to make the appeal; the ICC changed its playing conditions in 2011 to allow bowlers to run out a batsman backing up at any point prior to releasing the ball, rather than before entering his delivery stride, as the MCC Laws state.
Buttler's dismissal, alongside creating a potential flashpoint, deprived England of their firestarter-in-chief for the closing overs of the innings. Although each of the top eight made it into double figures, no one could go beyond Cook's stodgy 56, as they were bowled out for 219 with 11 deliveries remaining. Despite losing 3 for 7 in 21 balls and having to contend with the threat of rain throughout, Sri Lanka were not greatly taxed in overhauling their target.
The openers, Tillakaratne Dilshan and Kusal Perera, raised 50 together in the seventh over but Tredwell's introduction briefly threatened to turn the match. His second ball was crashed by Dilshan to cover, where Joe Root took a fabulous diving catch, before a pearler two overs later straightened on Kumar Sangakkara to clip the outside edge and be taken at slip. Kusal's dismissal, lbw to Anderson, left Sri Lanka 62 for 3 but England were left to regret a missed opportunity off Jayawardene when the batsman had 8 - a thick edge flying between Buttler and Jordan at slip - as a fourth-wicket stand of 98 carried the game away from them.

Read more at http://www.espn.co.uk/cricket/sport/story/312551.html#hJ7WB0GAXcCLfAMd.99

Proteins 'ring like bells'

          As far back as 1948, Erwin Schrödinger—the inventor of modern quantum mechanics—published the book "What is life?"

In it, he suggested that quantum mechanics and coherent ringing might be at the basis of all biochemical reactions. At the time, this idea never found wide acceptance because it was generally assumed that vibrations in protein molecules would be too rapidly damped.

Now, scientists at the University of Glasgow have proven he was on the right track after all.
Using modern laser spectroscopy, the scientists have been able to measure the vibrational spectrum of the enzyme lysozyme, a protein that fights off bacteria. They discovered that this enzyme rings like a bell with a frequency of a few terahertz or a million-million hertz. Most remarkably, the ringing involves the entire protein, meaning the ringing motion could be responsible for the transfer of energy across proteins.
The experiments show that the ringing motion lasts for only a picosecond or one millionth of a millionth of a second. Biochemical reactions take place on a picosecond timescale and the scientists believe that evolution has optimised enzymes to ring for just the right amount of time. Any shorter, and biochemical reactions would become inefficient as energy is drained from the system too quickly. Any longer and the enzyme would simple oscillate forever: react, unreact, react, unreact, etc. The picosecond ringing time is just perfect for the most efficient reaction.


These tiny motions enable proteins to morph quickly so they can readily bind with other molecules, a process that is necessary for life to perform critical biological functions like absorbing oxygen and repairing cells.
The findings have been published in Nature Communications.


Klaas Wynne, Chair in Chemical Physics at the University of Glasgow said: "This research shows us that proteins have mechanical properties that are highly unexpected and geared towards maximising efficiency. Future work will show whether these mechanical properties can be used to understand the function of complex living systems."

Reference :
http://phys.org/news/2014-06-proteins-bells.html

Basic Concepts of Differential Equations

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                           Differential Equations

 

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