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One of the most complex efforts toward a quantum computer has been shown off at the American Physical Society meeting in Dallas in the US. It uses the strange "quantum states" of matter to perform calculations in a way that, if scaled up, could vastly outperform conventional computers. The 6cm-by-6cm chip holds nine quantum devices, among them four "quantum bits" that do the calculations. The team said further scaling up to 10 qubits should be possible this year.
Rather than the ones and zeroes of digital computing, quantum computers deal in what are known as superpositions - states of matter that can be thought of as both one and zero at once. In a sense, quantum computing's one trick is to perform calculations on all superposition states at once. With one quantum bit, or qubit, the difference is not great, but the effect scales rapidly as the number of qubits rises. The figure often touted as the number of qubits that would bring quantum computing into a competitive regime is about 100, so each jump in the race is a significant one.
"It's pretty exciting we're now at a point that we can start talking about what the architecture is we're going to use if we make a quantum processor," Erik Lucero of the University of California, Santa Barbara told the conference. The team's key innovation was to find a way to completely disconnect - or "decouple" - interactions between the elements of their quantum circuit. The delicate quantum states that they create must be manipulated, moved, and stored without destroying them.
"It's a problem I've been thinking about for three or four years now, how to turn off the interactions," UCSB's John Martinis, who led the research," told BBC News. "Now we've solved it, and that's great - but there's many other things we have to do."
Qubits and pieces
The theory that our sense of smell has its basis in quantum physics events is gaining traction, say researchers. The idea remains controversial, but scientists reporting at the American Physical Society meeting in Dallas, US, are slowly unpicking how it could work. The key, they say, is tiny packets of energy, or quanta, lost by electrons. Experiments using tiny wires show that as electrons move on proteins within the nose, odor molecules could absorb these quanta and thereby be detected. If the theory is right, by extending these studies, an "electronic nose" superior to any chemical sensor could be devised.
Lock and key
The means by which a detected molecule is translated into a smell within the brain has already been the subject of Nobel prize-winning research. But how precisely an odorant molecule is detected remains a mystery. As with the picture of molecular interactions that drives our understanding of enzymes and drugs, the very shape of odorant molecules has been assumed to be the way it is detected in the nose. In this scenario, molecules are seen to be the "key" that fits neatly into a detector molecule in the nose that acts as a lock.
But in 1996, Luca Turin, now of the Massachusetts Institute of Technology in the US, suggested that the "vibrational modes" of an odorant were its signature. Molecules can be viewed as a collection of atoms on springs, and energy of just the right frequency - a quantum - can cause the spring to vibrate. Since different assemblages of molecules have different characteristic frequencies, Turin proposed, these vibrations could act as a molecular signature. The idea has been debated in the scientific literature, but presentations at the American Physical Society meeting put the theory on firmer footing.
Most recently, Dr Turin published a paper showing that flies can distinguish between molecules that are chemically similar but in which a heavier version of hydrogen had been substituted. Like a spring with a heavier weight at one end, the vibration frequency is lowered, and flies appear to notice. "There's still lots to understand, but the idea that it cannot possibly be right is no longer tenable really," said Andrew Horsfield of Imperial College London. "The theory has to at least be considered respectable at this point," he told BBC News.
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