Nobel Physics Prize Goes to Haroche and Wineland

Release date:2012-10-10 Page views:1038

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.

Dr. Wineland’s work has focused on the material side of where matter meets light. His prize is the fourth Nobel awarded to a scientist associated with the National Institute of Standards and Technology over the past 15 years for work involving the trapping and measuring of atoms. Dr. Wineland and his colleagues trap charged beryllium atoms, or ions, in an electric field and cool them with specially tuned lasers so that they are barely moving, which is another way of saying they are very, very cold.

Dr. Wineland said that much of the motivation for his work over the years came from the need for better and better clocks. “Historically,” he said in an interview with the Nobel committee, “when we have better clocks, we have better navigation.”

Atoms of any particular variety vibrate and emit light at very precise frequencies, and the colder or stiller those atoms are, the less the frequency of that light is blurred by atomic motions. As a result, Dr. Wineland and his colleagues have used their trapped ions to make the world’s most accurate clocks.

Modern-day atomic clocks are based on cesium atoms, which vibrate in the microwave range of frequencies, but visible light waves vibrate much faster than microwaves — every oscillation being a tick of the perfect clock. A new optical clock based on aluminum ions that emit visible light is about 10 times better than the cesium clock, Dr. Wineland said, and would be off by only five seconds over the whole course of cosmic time — 13.7 billion years.

The standards and technology institute’s work has also propelled the vision of quantum computing, in which ions — electrically charged atoms suspended in space — serve as the elements of the computation, the qubits.

In one set of experiments in the late 1990s, they tapped their beryllium ions with lasers with just enough energy to produce another kind of cat state and then watch it decay. In this one, the outermost electron in the ion was stuck between two of the permitted orbits around the beryllium nucleus; as a result they had an equal probability of being in either orbit and wound up in both orbits at once.

Resorting to the same analogy as Dr. Haroche, Dr. Wineland compared the electron to a marble rolling back and forth in a bowl. “At some instant of time, the marble is both on the left-hand side and the right side of bowl at the same time.”

In 1995, Dr. Wineland’s group used trapped ions to carry out a computation using a pair of ions as qubits. Recently researchers have done it with as many as 14 qubits, but a lot of work remains to be done, scientists say, before serious quantum computers are a reality.

“This is a long slow process,” Dr. Wineland said in a phone interview. “The kind of thing Serge and our group are doing is part of an evolution of a technology. We’re getting better and better at it as we go along.”

He added, “We haven’t had a breakthrough with quantum computing yet, but for certain problems the promise is there.”

More information in   A Nobel for Teasing Out the Secret Life of Atoms

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