Friday, October 19, 2007

Swiss elections get spooky
[This is my latest column for muse@nature.com.]

High-profile applications of quantum trickery raise the question of what to call these new technologies. One proposal is unlikely to catch on.

The use of quantum cryptography in the forthcoming Swiss general elections on 21 October may be a publicity stunt, but it highlights the fact that the field of quantum information is now becoming an industry.

The invitation here is to regard Swiss democracy as being safeguarded by the fuzzy shroud of quantum physics, which can in principle provide a tamper-proof method of transmitting information. The reality is that just a single state – Geneva – is using commercial quantum-cryptography technology already trialled by banks and financial institutions, and that it is doing so merely to send tallies from a vote-counting centre to the state government’s repository.

The votes themselves are being delivered by paper ballot – which, given the controversies over electronic voting systems, is probably still the most secure way to collect them. In any event, with accusations of overt racism in the campaigning of the right-wing Swiss People’s Party (SVP), hacking of the voting system is perhaps the least of the worries in this election.

But it would be churlish to portray this use of quantum cryptography as worthless. There is no harm in using a high-profile event to advertise the potential benefits of the technology. If nothing else, it will get people asking what quantum cryptography is.

The technique doesn’t actually make transmitted data invulnerable to tampering. Instead, it makes it impossible to interfere with the transmission without leaving a detectable trace. Some quantum cryptographic schemes use the quantum-mechanical property of entanglement, whereby two or more quantum particles are woven together so that they become a single system. Then you can’t do something to one particle without affecting the others with which it is entangled.

Entanglement isn’t essential for quantum encryption – the first such algorithm, devised by physicists Charles Bennett and Gilles Brassard in 1984, instead relies on a property called quantum indeterminacy, denoting our fundamental inability to describe some quantum systems exactly. Entanglement, however, is the key to a popular scheme devised in 1991. Here, the sender and receiver each receive one of a pair of entangled particles, and can decode a message by comparing their measurements of the particles’ quantum states. Any eavesdropping tends to randomize the relationship between these states, and is therefore detectable.

Quantum cryptography is just one branch of the emerging discipline of quantum information technology, in which phenomena peculiar to the quantum world, such as entanglement, are used to manipulate information. Other applications include quantum computing, in which quantum particles are placed in superposition states – mixtures of the classical states that would correspond to the binary 1’s and 0’s of ordinary computers – to vastly boost the power and capacity of computation. Quantum teleportation – the exact replication of quantum particles at locations remote from the originals – also makes use of entanglement.

The roots of these new areas of quantum physics lie in the early days of quantum theory, when its founders were furiously debating what quantum theory implied about the physical world. Albert Einstein, whose Nobel-winning explanation of the photoelectric effect was one of the cornerstones of quantum mechanics, doubted that quantum particles could really have the fuzzy properties ascribed to them by the theory, to which one could do no more than assign probabilities.

In 1935 Einstein and his colleagues Boris Podolsky and Nathan Rosen proposed a thought experiment that they hoped would show quantum theory to be an incomplete account of physical reality. They showed how it seemed to predict what Einstein called ‘spooky action at a distance’ that operated instantaneously between two particles.

But we now know that this action at a distance is real – it is the result of quantum entanglement. What Einstein considered a self-evident absurdity is simply the way the world is. What’s more, entanglement and superpositions are now recognized as being key to the way our deterministic classical world, where events have definite outcomes, emerges from the murky haze of quantum probabilities.

Bennett was one of the pioneers who showed that these quantum effects aren’t just abstract curiosities, but can be exploited in applications. For this, he will surely get a Nobel prize some time soon.

So far, most researchers have been happy to talk about ‘quantum cryptography’, ‘quantum computing’ and so forth, vaguely gathered under the umbrella phrase of quantum information. But is that a good name for a technology? Charles Tahan, a physicist at the University of Cambridge who is working on these technologies, thinks not. In a recent preprint, he proposes to draw inspiration from Einstein and call it all ‘spookytechnology’.

This, says Tahan, would refer to “all functional devices, systems and materials whose utility relies in whole or in part on higher order quantum properties of matter and energy that have no counterpart in the classical world.” By higher-order, Tahan means things like entanglement and superposition. He argues that his definition is broad enough to contain more than quantum information technology, but not so broad as to be meaningless.

In that respect, Tahan points to the shortcomings of ‘nanotechnology’, a field that is not really a field at all but instead a ragbag of many areas of science and technology ranging from electronics to biomedicine.

But Tahan's label will never stick, because it violates one of the most fundamental prohibitions in scientific naming: don’t be cute. No scientist is going to want to tell people that he or she is working in a field that sounds as though it was invented by Caspar the Friendly Ghost. True, the folksy ‘buckyballs’ gained some currency as a term for the fullerene carbon molecules (despite Nature’s best efforts) – but its usage remains a little marginal, and has thankfully never caught on for ‘buckytubes’, which everyone instead calls carbon nanotubes.

Attempts to label nascent fields rarely succeed, for names have a life of their own. ‘Nanotechnology’, when coined in 1974, had nothing like the meaning it has today. ‘Spintronics’, the field of quantum electronics that in some sense lies behind this year’s physics Nobel, is arguably a slightly ugly and brutal amalgam of electronics and the quantum property of electrons called spin - yet somehow it works.

Certainly, names need to be catchy: laboured plunderings of Greek and Latin are never popular. But catchiness is extremely hard to engineer. So somehow I don’t think we’re going to see the Geneva elections become a landmark in spookytechnology.

3 comments:

JimmyGiro said...

Shock result at the Swiss elections, as the President is beaten into second place by his own wave function.

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