When quantum theory was born, practical applications such as quantum computers and super-accurate atomic clocks would have seemed virtually impossible. This year's Nobel prize in physics, announced this morning, rewards two pioneers who made today's quantum technology possible.
Serge Haroche at Ecole Normale Supérieure in Paris, France, and David Wineland at the US National Institute of Standards and Technology and the University of Colorado, Boulder, who share the 2012 physics Nobel, both invented ways to measure and control tiny quantum objects without destroying their fragile states. This bodes well for quantum computers, devices that exploit the weird properties of quantum systems to solve problems that stymie ordinary computers.
Wineland's work has already helped him build the world's most precise clock for studying Einstein's theory of relativity.
Haroche was awarded the prize for his work on optical cavities, small superconducting mirrors placed just a few centimetres apart and cooled to just above absolute zero. A photon entering the cavity can bounce between the mirrors for more than a tenth of a second, long enough to travel 40,000 kilometres.
Caging photons in this way lets you investigate their quantum behaviour. Haroche fires rubidium atoms one by one into the cavity, where they interact with the photon before passing out the other side. This atomic drive-by shifts the atom's quantum state but, crucially, does not destroy the photon. In this way Haroche can measure the atom and learn about the detailed evolution of the photon's state over time.
Wineland's work takes the opposite approach: he traps charged atoms or ions within electric fields and fires lasers at them to force the ions into a particular quantum state.
The lasers cool the ions by suppressing random motion due to heat, forcing them into their lowest energy state. Precise laser pulses can then boost the energy of the ions by a tiny amount, creating a quantum superposition in which the ion has an equal chance of occupying both the lowest energy state and the next one up.
"Until the last decade or two, some of these results were nothing more than ideas in science fiction or, at best, the wilder imaginations of quantum physicists," says Jim Al-Khalili at the University of Surrey in Guildford, UK. "Wineland and Haroche and their teams have shown just how strange the quantum world really is and opened up the potential for new technologies undreamt of not so long ago."
Those technologies include a quantum computer. In 1995, Wineland's group demonstrated the first quantum logic gate , an essential precursor to quantum computing.
His technique is also key to the world's most precise clock, which keeps time via the regular oscillations of a trapped aluminium ion. The clock is so precise that, had it started ticking at the dawn of the universe, it would have only lost about 4 seconds by now.
Such clocks are precise enough to measure the slowing of time caused by changes in gravity, as predicted by Einstein's theory of relativity.
Neither laureate appeared in a list of predictions released ahead of the Nobel announcement, but Haroche got a warning of a sort. Speaking via phone line at the Nobel Prize press conference, he said he was out walking with his wife when his phone rang. The country code displayed, 46, alerted him that the call was from Sweden. "I was in the street and passing near a bench. I was able to sit down immediately," he says.