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Cavity Quantum Electrodynamics be greatly suppressed or enhanced by placing the atoms between mirrors or in cavities. Serge Haroche; Daniel Kleppner. With further refinement of this technology, cavity quantum electrodynamic (QED) In one of us (Haroche), along with other physicists at Yale University. Atomic cavity quantum electrodynamics reviews: J. Ye., H. J. Kimble, H. Katori, Science , (). S. Haroche & J. Raimond, Exploring the Quantum.

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Small cavities suppress atomic transitions; slightly larger ones, however, electeodynamics enhance them. If one prepares the atom itself favity a superposition of two states, one of which is delayed by the cavity while the other is unaffected, then the atomic wave packet itself will be split into two parts.

When the size of a cavity surrounding an excited atom is increased to the point where it matches the wavelength of the photon that the atom would naturally emit, vacuum-field fluctuations at that wavelength flood the cavity and become stronger than they would be in free space. The suppression of spontaneous emission at an optical frequency requires much smaller cavities.

Cavity Quantum Electrodynamics |

For Rydberg atoms in a microwave cavity with a typical exchange frequency of kilohertz, the potential energy difference is about one ten-billionth of an electron volt. A cavity with no photon is in its lowest-energy state, the so-called ground state, but it is not really empty. This photon typically has a wavelength of a micron or less, corresponding to a frequency of a few hundred terahertz and an energy of about one electron volt.

Eventually, however, an atom deposits a photon; then the next atom in line encounters sharply altered odds that it will emit energy. From Wikipedia, the free encyclopedia. Yet during the past decade, this inevitability has begun to yield. Retrieved from ” https: I will describe CQED experiments in which microwave photons are controlled and manipulated non destructively by Rydberg atoms crossing the cavity one by one.


To detect the atom’s position after it has passed through the cavity, researchers could fire an array of field ionization detectors simultaneously some time after the launch of each atom.

In fact, the radio waves cannot propagate unless the tunnel walls are separated by more than half a wavelength. Sign up for our email newsletter. This state of affairs haroce typically last up to a fraction of a second, long enough for the atom to travel through the centimeter-size cavity. If the system is in the lower-energy state, the interaction attracts the atom to the cavity center.

Cavity quantum electrodynamics

Before measurement, of course, the photon number is not merely a classically unknown quantity. For a mismatch of a few billionths of an electron volt, the elrctrodynamics typically lasts a few nanoseconds.

These effects, which depend on intimate long-term interactions between the excited atom and the cavity, are the basis for a series of new devices that can make sensitive measurements of quantum phenomena. If a photon disappears in the cavity walls, that disappearance would register immediately in the atomic interference pattern.

The Yale researchers demonstrated these polarization-dependent effects by rotating the atomic dipole between the mirrors with the help ekectrodynamics a magnetic field.

They can even interfere with themselves. The vacuum field bounded by the cavity walls polarizes the Rydberg atom, and the spatial variations of the field produce a net force.

Although this characteristic seems to be merely what one would ask of any measurement, it is impossible to attain by conventional means. Light waves are moving oscillations of electric and magnetic fields.

An atom in a Rydberg state has almost enough energy to lose an electron completely. The experiments performed on atoms between two flat mirrors have an interesting twist. It also usually contains an inherent quantum uncertainty. Such states are extremely fragile, and the techniques developed to create and measure CQED states are now being applied to the development of quantum computers. The Heisenberg uncertainty principle permits the atom briefly to borrow enough energy to emit a photon whose energy exceeds the difference between the top level and the middle one, provided that this loan is paid back during the emission of the second photon.


Haroche focused on microwave experiments and turned the technique on its head — using CQED to control the properties of individual photons. How can such a paradoxical situation exist? This state of affairs encourages emission; the lifetime of the excited state becomes much shorter than it would naturally be. In any given run, however, the photon number will remain constant, once pinned down.

Aboutatoms per second can pass through a typical micromaser each remaining perhaps 10 microseconds ; meanwhile the photon lifetime within the cavity is typically about 10 milliseconds. These atoms are prepared in a state whose favored transition matches the resonant frequency of the cavity between 20 and 70 gigahertz. When the atom enters the cavity, the exchange coupling works to separate the two states, so that the state with an excited atom and no photon branches unambiguously into the higher-energy steady state, in which the atom is repelled.

Of course, that is not strictly true, because if the cavity is empty, the atom has to be initially excited, and some price is paid after all.