Two physicists who developed techniques to peer in on the most intimate relations between light and matter won the Nobel Prize in Physics on Tuesday. They are Serge Haroche, 68, of the Collège de France and the École Normale Supérieure, in Paris, and David J. Wineland, also 68, of the National Institute of Standards and Technology and the University of Colorado.
They will split eight million Swedish krona, or about $1.2 million, and receive their award in Stockholm on Dec. 10.
Their work, the academy said, enables scientists to directly observe some of the most bizarre effects — like the subatomic analogue of cats that are alive and dead at the same time — predicted by the quantum laws that prevail in the microcosm, and could lead eventually to quantum computers and superaccurate clocks.
Reached by the Nobel committee while walking with his wife on Tuesday morning in Paris, Dr. Haroche saw on his phone where the call was coming from and, he said, had to sit down on a bench. "It was real," he said in a phone news conference.
Scientists have known for a hundred years now that atoms behave oddly. On the smallest scales of nature, the common-sense laws of science are overthrown by the strange house rules of quantum mechanics, in which physical systems are represented by mathematical formulations called wave functions that encapsulate all the possibilities of some event or object.
Light or a subatomic particle like an electron could be a wave or a particle depending on how you want to look at it, and causes are not guaranteed to be linked to effects. An electron could be in two places at once, or everywhere until someone measures it, courtesy of the Heisenberg uncertainty principle, which caused a cranky Einstein to grumble that God did not play dice.
Erwin Schrödinger, one of the founders of the theory — as was Einstein, for that matter — once complained that according to quantum principles a cat in a box would be both alive and dead until somebody looked at it.
Until recent years this was all philosophy, and physicists could comfort themselves with the realization that quantum mechanics works so spectacularly well — every time you turn on your computer, for example — that for some of them the real problem is why the ordinary world does not work that way; why, for example, your sunglasses are not simultaneously in the car, back at the summer cabin or on the shelf when you want them.
Now scientists are able to direct experiments and catch nature in the act of being quantum and thus explore the boundary between quantum reality and normal life. Their work involves isolating the individual nuggets of nature — atoms and the particles that transmit light, known as photons — and making them play with each other.
Dr. Haroche and Dr. Wineland, who have been good friends for 25 years, have approached the dance between matter and light from opposite sides. Dr. Haroche traps photons in a mirrored cavity whose walls are so finely polished that one photon will bounce back and forth for a tenth of a second — an eternity in atomic physics — before leaking out or being absorbed. Then he sends in a single atom, as a spy, to interact with the light.
Normally, to detect light is to destroy it, since photons are absorbed in our retinas or in the chips in our cameras. But in one case, by observing subtle effects of the light on the atoms, he and his colleagues could count the photons — "as one would do with marbles in a box," as he put it on his Web site — without destroying them.
In another case, in 1996, Dr. Haroche and his colleagues raised Schrödinger's cat from the undead by putting their boxed photon into a "cat state" in which it was out of phase with itself, essentially oscillating in opposite directions at the same time. Then by sending in their spy atoms, they measured how long it took for the "cat state" to decay — or decohere in quantumspeak — and the photon to oscillate in one direction or the other.
In more recent experiments, they have developed feedback techniques to keep the cat state going longer. Such techniques are crucial for the dream of quantum computers, which manipulate so-called qubits that are 1 and 0 simultaneously to solve some problems like factoring gigantic numbers to break codes beyond the capacity of ordinary computers. Such computers depend on the ability to isolate their "qubits" from the environment to preserve their magical computing powers, but at the same time there must be a way to measure the qubits to read out their answer.
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