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Quantum optics work wins physics Nobel

EuroPhotonics
Dec 2012
STOCKHOLM – Separate but related quantum optics technologies – ions in a harmonic trap and photons in a cavity – that allow the measurement and control of individual quantum systems were recognized by the Royal Swedish Academy of Sciences with the 2012 Nobel Prize in physics.

Serge Haroche of the Collège de France and Ecole Normale Supérieure in Paris and David J. Wineland of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder will share the $1.2 million (SEK 8 million) prize for their independent research, which created methods for measuring, manipulating and observing individual quantum particles without destroying their quantum mechanical nature.


In the Serge Haroche laboratory in Paris, in vacuum and at a temperature of almost absolute zero, the microwave photons bounce back and forth inside a small cavity between two mirrors. The mirrors are so reflective that a single photon stays for more than a tenth of a second before it is lost. During its long lifetime, many quantum manipulations can be performed with the trapped photon without destroying it. Courtesy of The Royal Swedish Academy of Sciences.


Although developed separately over many years by their teams in the US and France, their work is synergistic, the academy said.

“I use atoms to study photons, and he uses photons to study atoms,” Haroche said in a phone interview with Nobelprize.org of his and Wineland’s work. “He is a friend, and I admire his work very much. I’m very glad to share the prize with him.”

The field of quantum optics, which deals with the interaction between light and matter, has seen considerable progress since the mid-1980s, the academy said. Because single particles are not easily isolated from their surrounding environment and lose their mysterious quantum properties as soon as they interact with the outside world, it was thought that direct observation could not be attained; researchers could carry out thought experiments that only might, in principle, manifest the bizarre phenomena.

Wineland and Haroche’s groundbreaking methods have enabled the field to take the very first steps toward building a new type of superfast computer based on quantum physics, the academy said, adding, “Perhaps the quantum computer will change our everyday lives in this century in the same radical way as the classical computer did in the last century.”

In Wineland’s lab, electrically charged atoms (ions) are kept inside a trap by surrounding them with electric fields. The particles are isolated from the heat and radiation in their environment by performing the experiments in vacuum at cryogenic temperatures. One secret behind his breakthrough is using a laser to suppress the ion’s thermal motion in the trap, putting it in its lowest energy state and enabling the study of quantum phenomena with the trapped ion.

A carefully tuned laser pulse can be used to prepare the ion so that it occupies two different energy levels simultaneously. It starts in a lowest energy level, and the laser pulse nudges the ion halfway toward a higher energy level so that it is left in between the two levels, in a superposition of energy states and with an equal probability of ending up in either of them. In this way, a quantum superposition of the ion’s energy states can be studied.

Haroche and his group employ a different method to reveal the mysteries of the quantum world. In their laboratory in Paris, microwave photons bounce back and forth inside a small cavity between two mirrors, about 3 cm apart. The mirrors are made of superconducting material and are cooled to a temperature just above absolute zero. They are so reflective that a single photon can bounce back and forth inside the cavity for almost a tenth of a second before it is lost or absorbed – an enormous length of time for a photon during which many quantum manipulations can be performed with the trapped light particle.

Haroche uses specially prepared Rydberg atoms, which are roughly 1000 times larger than typical atoms, to both control and measure the microwave photon in the cavity. These gigantic doughnut-shaped atoms are sent into the cavity one by one at a carefully chosen speed, so that the interaction with the microwave photon occurs in a well-controlled manner. The atom traverses and exits the cavity, leaving the microwave photon behind. But the interaction between the photon and the atom creates a change in the phase of quantum state of the atom, shifting it. This phase shift can be measured when the atom exits the cavity, revealing the presence or absence of a photon inside the cavity and allowing Haroche to measure a single photon without destroying it.

The physicists’ work also has led to the construction of extremely precise optical clocks that could become the future basis for a new standard of time – with more than a hundredfold greater precision than present-day cesium clocks, which operate in the microwave range.

Wineland’s ion clocks use visible light. Such an optical clock can consist of just one ion or two ions in a trap. With two ions, one is used as the clock and the other, to read the clock without destroying its state or causing it to miss a beat. The precision of an optical clock is better than one part in 1017, which means that if one had started to measure time at the beginning of the universe about 14 billion years ago, the optical clock would be off by only about 5 seconds today.

Haroche was born in Casablanca in 1944. He obtained his PhD from Paris VI University in 1971. His research in quantum optics and quantum information science has mostly taken place in Kastler Brossel Laboratory at ENS.

Wineland was born in Milwaukee in 1944. He studied at the University of California, Berkeley, obtaining his PhD from Harvard University in 1970. His work has included advances in optics, specifically in quantum computing.


GLOSSARY
microwave
An electromagnetic wave lying within the region of the frequency spectrum that is between about 1000 MHz (1 GHz) and 100,000 MHz (100 GHz). This is equivalent to the wavelength spectrum that is between one millimeter and one meter, and is also referred to as the infrared and short wave spectrum.
photon
A quantum of electromagnetic energy of a single mode; i.e., a single wavelength, direction and polarization. As a unit of energy, each photon equals hn, h being Planck's constant and n, the frequency of the propagating electromagnetic wave. The momentum of the photon in the direction of propagation is hn/c, c being the speed of light.
quantum
Smallest amount into which the energy of a wave can be divided. The quantum is proportional to the frequency of the wave. See photon.
quantum mechanics
The science of all complex elements of atomic and molecular spectra, and the interaction of radiation and matter.
quantum optics
The area of optics in which quantum theory is used to describe light in discrete units or ‘quanta’ of energy known as photons. First observed by Albert Einstein’s photoelectric effect, this particle description of light is the foundation for describing the transfer of energy (i.e. absorption and emission) in light matter interaction.
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