. Dans-le-régime-où-le-flux-atomique-est-faible, On peut négliger des effets de couplage collectif. Le gain est alors donné par la proportion d'atomes qui ont laissé un photon dans la cavité par unité de temps: où 03A6 at est le flux atomique. La durée de la mesure est donnée par l'étalement du paquet d'atomes au niveau de la cavité, qui est grand devant le temps d'amortissement t cav, Nous ne nous intéressons donc qu'à la situation d'équilibre où le gain est égal au pertes. Ceci est exprimé par l'équation

]. S. Références, D. Haroche, and . Kleppner, Cavity quantum electrodynamics, Physics Today, vol.42, issue.24, 1989.

E. M. Purcell, Spontaneous Emission Probabilities at Radio Frequencies, Phys. Rev, vol.69, p.681, 1946.
DOI : 10.1007/978-1-4615-1963-8_40

H. B. Casimir and D. Polder, The Influence of Retardation on the London-van der Waals Forces, Physical Review, vol.73, issue.4, p.360, 1948.
DOI : 10.1103/PhysRev.73.360

H. Morawitz, Self-Coupling of a Two-Level System by a Mirror, Physical Review, vol.187, issue.5, p.1792, 1969.
DOI : 10.1103/PhysRev.187.1792

G. Barton, Quantum Electrodynamics of Spinless Particles between Conducting Plates, Proc. Roy. Soc. London A320, p.251, 1970.
DOI : 10.1098/rspa.1970.0208

M. Babiker and G. Barton, Quantum electrodynamics between conducting plates

P. W. Milonni, J. R. Ackerhalt, and W. A. Smith, Interpretation of Radiative Corrections in Spontaneous Emission, Physical Review Letters, vol.31, issue.15, p.958, 1973.
DOI : 10.1103/PhysRevLett.31.958

P. W. Milonni and P. L. Knight, Spontaneous emission between mirrors, Optics Communications, vol.9, issue.2, p.119, 1973.
DOI : 10.1016/0030-4018(73)90239-3

M. Babiker and G. Barton, Quantum frequency shifts near a plasma surface, Journal of Physics A: Mathematical and General, vol.9, issue.1, p.129, 1976.
DOI : 10.1088/0305-4470/9/1/018

G. S. Agarwal, Quantum electrodynamics in the presence of dielectrics and conductors. IV. General theory for spontaneous emission in finite geometries, Physical Review A, vol.12, issue.4, p.1475, 1975.
DOI : 10.1103/PhysRevA.12.1475

]. G. Barton, The interaction of an atom with electromagnetzc vacuum fluctuations in the presence of a pair of perfectly conducting plates, Proc. Roy. Soc. London A367, pp.164-117, 1979.

D. Kleppner, Inhibited Spontaneous Emission, Physical Review Letters, vol.47, issue.4, p.233, 1981.
DOI : 10.1103/PhysRevLett.47.233

C. A. Lütken and F. , Energy-level shifts in atoms between metallic planes, Physical Review A, vol.31, issue.4, p.2082, 1985.
DOI : 10.1103/PhysRevA.31.2082

J. M. Wylie and J. E. Sipe, Quantum electrodynamics near an interface. II, Physical Review A, vol.32, issue.4, p.2030, 1985.
DOI : 10.1103/PhysRevA.32.2030

G. Barton, Quantum-Electrodynamic Level Shifts between Parallel Mirrors: Applications, Mainly to Rydberg States, Proc. Roy. Soc. London A410, p.175, 1987.
DOI : 10.1098/rspa.1987.0033

P. Goy, J. M. Raimond, M. Gross, and E. S. Haroche, Observation of Cavity-Enhanced Single-Atom Spontaneous Emission, Physical Review Letters, vol.50, issue.24, p.1903, 1983.
DOI : 10.1103/PhysRevLett.50.1903

D. J. Heinzen, J. J. Childs, J. E. Thomas, and M. S. Feld, Enhanced and Inhibited Visible Spontaneous Emission by Atoms in a Confocal Resonator, Phys. Rev

F. De-martini, G. Innocenti, G. R. Jacobovitz, and E. P. Mataloni, Anomalous Spontaneous Emission Time in a Microscopic Optical Cavity, Physical Review Letters, vol.60, issue.15, p.2955, 1987.
DOI : 10.1103/PhysRevLett.60.1590

R. G. Hulet, E. S. Hilfer, and E. D. Kleppner, Inhibited Spontaneous Emission by a Rydberg Atom, Physical Review Letters, vol.55, issue.20, p.2137, 1985.
DOI : 10.1103/PhysRevLett.55.2137

W. Jhe, A. Anderson, E. A. Hinds, D. Meschede, L. Moi et al., Suppression of spontaneous decay at optical frequencies: Test of vacuum-field anisotropy in confined space, Physical Review Letters, vol.58, issue.7, p.666, 1987.
DOI : 10.1103/PhysRevLett.58.666

S. Haroche, Rydberg atoms and radiation in a resonant cavity New Trends in Atomic Physics, volume Session XXXVIII of Les Houches Summer School, 1982.

S. Haroche and J. M. Raimond, Radiative Properties of Rydberg States in Resonant Cavities, Advances in Atomic and Molecular Physics, 1985.
DOI : 10.1016/S0065-2199(08)60271-7

H. Walther, The Single Atom Maser and the Quantum Electrodynamics in a Cavity, Physica Scripta, vol.23, p.165, 1988.
DOI : 10.1088/0031-8949/1988/T23/031

G. Rempe, H. Walther, and E. N. Klein, Observation of quantum collapse and revival in a one-atom maser, Physical Review Letters, vol.58, issue.4, p.353, 1987.
DOI : 10.1103/PhysRevLett.58.353

F. Bernardot, P. Nussenzveig, M. Brune, J. M. Raimond, and E. S. Haroche, Vacuum Rabi Splitting Observed on a Microscopic Atomic Sample in a Microwave Cavity, Europhysics Letters (EPL), vol.17, issue.1, p.33, 1992.
DOI : 10.1209/0295-5075/17/1/007

R. J. Thompson, G. Rempe, and H. J. Kimble, Observation of normal-mode splitting for an atom in an optical cavity, Physical Review Letters, vol.68, issue.8, p.1132, 1992.
DOI : 10.1103/PhysRevLett.68.1132

D. Meschede, H. Walther, and G. Müller, One-Atom Maser, Physical Review Letters, vol.54, issue.6, p.551, 1985.
DOI : 10.1103/PhysRevLett.54.551

M. Brune, J. M. Raimond, P. Goy, L. Davidovich, and E. S. Haroche, Realization of a two-photon maser oscillator, Physical Review Letters, vol.59, issue.17, p.1899, 1987.
DOI : 10.1103/PhysRevLett.59.1899

J. A. Gallas, G. Leuchs, H. Walther, and H. Figger, Rydberg Atoms: High-Resolution Spectroscopy and Radiation Interaction???Rydberg Molecules, Advances in Atomic and Molecular Physics, 1985.
DOI : 10.1016/S0065-2199(08)60272-9

V. B. Braginsky, Y. I. Vorontsov, and F. Y. Khalili, Quantum singularities of a ponderomotive meter of electromagnetic energy, Sov. Phys. JETP, vol.46, p.705, 1977.

W. G. Unruh, Analysis of quantum-nondemolition measurement, Physical Review D, vol.18, issue.6, p.1764, 1978.
DOI : 10.1103/PhysRevD.18.1764

C. M. Caves, K. S. Thorne, R. W. Drever, V. D. Sandberg, and E. M. Zimmermann, On the measurement of a weak classical force coupled to a quantum-mechanical oscillator. I. Issues of principle, Reviews of Modern Physics, vol.52, issue.2, p.431, 1980.
DOI : 10.1103/RevModPhys.52.341

E. Schrödinger, Die gegenw???rtige Situation in der Quantenmechanik, Proc. Am, pp.844-3325, 1935.
DOI : 10.1007/BF01491987

M. Brune, S. Haroche, V. Lefèvre, J. M. Raimond, and E. N. Zagury, Quantum nondemolition measurement of small photon numbers by Rydberg-atom phase-sensitive detection, Physical Review Letters, vol.65, issue.8, p.976, 1990.
DOI : 10.1103/PhysRevLett.65.976

M. Brune, S. Haroche, J. M. Raimond, L. Davidovich, and E. N. Zagury, Manipulation of photons in a cavity by dispersive atom-field coupling: Quantum-nondemolition measurements and generation of ??????Schr??dinger cat?????? states, Physical Review A, vol.45, issue.7, p.5193, 1992.
DOI : 10.1103/PhysRevA.45.5193

R. G. Hulet and D. Kleppner, Rydberg Atoms in "Circular" States, Physical Review Letters, vol.51, issue.16, p.1430, 1983.
DOI : 10.1103/PhysRevLett.51.1430

P. Nussenzveig, F. Bernardot, M. Brune, J. Hare, J. M. Raimond et al., Preparation of high-principal-quantum-number ??????circular?????? states of rubidium, Physical Review A, vol.48, issue.5, p.3991, 1993.
DOI : 10.1103/PhysRevA.48.3991

M. Brune, P. Nussenzveig, F. Schmidt-kaler, F. Bernardot, A. Maali et al., From Lamb shift to light shifts: Vacuum and subphoton cavity fields measured by atomic phase sensitive detection, Physical Review Letters, vol.72, issue.21, p.3339, 1994.
DOI : 10.1103/PhysRevLett.72.3339

N. F. Ramsey, A Molecular Beam Resonance Method with Separated Oscillating Fields, Physical Review, vol.78, issue.6, p.695, 1950.
DOI : 10.1103/PhysRev.78.695

N. F. Ramsey, Molecular Beams, 1985.

S. Haroche, Cavity Quantum Electrodynamics, Fundamental Systems in Quantum Optics, volume Session LIII of Les Houches Summer School, 1990.
DOI : 10.1063/1.881201
URL : https://hal.archives-ouvertes.fr/hal-00001585

S. Haroche and J. M. Raimond, Manipulation of non-classical field states in a cavity by atom interferometry, Advances in Atomic, Molecular and Optical Physics, vol.32, 1994.

S. Haroche, M. Brune, J. M. Raimond, and E. L. Davidovich, Mesoscopic quantum coherences in cavity QED, Fundamentals of Quantum Optics III. Proceedings of the Fifth Meeting on Laser Phenomena, 1993.
DOI : 10.1007/BFb0113568

V. B. Braginsky and F. Y. Khalili, Optico-magnetic effects in nondestructive quantum counting, Sov. Phys. JETP, vol.51, p.859, 1980.

M. D. Levenson, R. M. Shelby, M. Reid, and D. F. Walls, Quantum Nondemolition Detection of Optical Quadrature Amplitudes, Physical Review Letters, vol.57, issue.20, p.2473, 1986.
DOI : 10.1103/PhysRevLett.57.2473

P. Grangier, J. F. Roch, and E. G. Roger, Observation of backaction-evading measurement of an optical intensity in a three-level atomic nonlinear system, Physical Review Letters, vol.66, issue.11, p.1418, 1991.
DOI : 10.1103/PhysRevLett.66.1418
URL : https://hal.archives-ouvertes.fr/hal-00559097

L. Allen and J. H. Eberly, Optical Resonance and Two-Level Atoms, 1975.

E. T. Jaynes and F. W. Cummings, Comparison of quantum and semiclassical radiation theories with application to the beam maser, Proc. IEEE 51, p.89, 1963.
DOI : 10.1109/PROC.1963.1664

A. Faist, E. Geneux, P. Meystre, and E. A. Quattropani, Rayonnement cohérent en interaction avec un système à deux niveaux, Helv. Phys. Acta, vol.45, p.956, 1972.

J. H. Eberly, N. B. Narozhny, and J. J. Sanchez-mondragon, Periodic Spontaneous Collapse and Revival in a Simple Quantum Model, Physical Review Letters, vol.44, issue.20, p.1323, 1980.
DOI : 10.1103/PhysRevLett.44.1323

P. L. Knight and P. M. Radmore, Quantum origin of dephasing and revivals in the coherent-state Jaynes-Cummings model, Physical Review A, vol.26, issue.1, p.676, 1982.
DOI : 10.1103/PhysRevA.26.676

C. Cohen-tannoudji, Atomic motion in laser light, Fundamental Systems in Quantum Optics, volume Session LIII of Les Houches Summer School, 1990.

S. Haroche, M. Brune, and J. M. Raimond, Trapping Atoms by the Vacuum Field in a Cavity, Europhysics Letters (EPL), vol.14, issue.1, p.19, 1991.
DOI : 10.1209/0295-5075/14/1/004

B. G. Englert, J. Schwinger, A. O. Barut, and M. O. Scully, Reflecting Slow Atoms from a Micromaser Field, Europhysics Letters (EPL), vol.14, issue.1, p.25, 1991.
DOI : 10.1209/0295-5075/14/1/005

F. Treussart, J. Hare, L. Collot, V. Lefèvre, D. Weiss et al., Quantized atom-field force at the surface of a microsphere, Optics Letters, vol.19, issue.20, 1994.
DOI : 10.1364/OL.19.001651

M. O. Scully and H. Walther, Quantum optical test of observation and complementarity in quantum mechanics, Physical Review A, vol.39, issue.10, p.5229, 1989.
DOI : 10.1103/PhysRevA.39.5229

M. O. Scully, B. G. Englert, and E. H. Walther, Quantum optical tests of complementarity, Nature, vol.351, issue.6322, p.111, 1991.
DOI : 10.1038/351111a0

N. Lu, Effects of dissipation on photon statistics and the lifetime of a pure number state, Physical Review A, vol.40, issue.3, p.1707, 1989.
DOI : 10.1103/PhysRevA.40.1707

S. Haroche, M. Brune, and J. M. Raimond, Measuring photon numbers in a cavity by atomic interferometry: optimizing the convergence procedure, Journal de Physique II, vol.2, issue.4, p.659, 1992.
DOI : 10.1051/jp2:1992157
URL : https://hal.archives-ouvertes.fr/jpa-00247663

T. Sauter, W. Neuhauser, R. Blatt, and P. E. Toschek, Observation of Quantum Jumps, Physical Review Letters, vol.57, issue.14, p.1696, 1986.
DOI : 10.1103/PhysRevLett.57.1696

J. C. Bergquist, R. G. Hulet, W. M. Itano, and D. J. Wineland, Observation of Quantum Jumps in a Single Atom, Physical Review Letters, vol.57, issue.14, p.1699, 1986.
DOI : 10.1103/PhysRevLett.57.1699

B. Yurke and D. Stoler, Generating quantum mechanical superpositions of macroscopically distinguishable states via amplitude dispersion, Physical Review Letters, vol.57, issue.1, p.13, 1986.
DOI : 10.1103/PhysRevLett.57.13

G. J. Milburn and C. A. Holmes, Dissipative Quantum and Classical Liouville Mechanics of the Anharmonic Oscillator, Physical Review Letters, vol.56, issue.21, p.2237, 1986.
DOI : 10.1103/PhysRevLett.56.2237

G. J. Milburn, Quantum and classical Liouville dynamics of the anharmonic oscillator, Physical Review A, vol.33, issue.1, p.674, 1986.
DOI : 10.1103/PhysRevA.33.674

W. H. Zurek, Decoherence and the Transition from Quantum to Classical, Physics Today, vol.44, issue.10
DOI : 10.1063/1.881293

W. Meissner and R. Ochsenfeld, Ein neuer Effekt bei Eintritt der Supraleitf???higkeit, Die Naturwissenschaften, vol.21, issue.44, p.787, 1933.
DOI : 10.1007/BF01504252

M. Zimmerman, M. Littman, M. Kash, and E. D. Kleppner, Stark structure of the Rydberg states of alkali-metal atoms, Physical Review A, vol.20, issue.6, p.2251, 1979.
DOI : 10.1103/PhysRevA.20.2251

M. Gross and J. Liang, Is a circular Rydberg atom stable in a vanishing electric field?, Physical Review Letters, vol.57, issue.25, p.3160, 1986.
DOI : 10.1103/PhysRevLett.57.3160

H. A. Bethe and E. E. Salpeter, Quantum Mechanics of One-and Two-Electron Atoms, 1977.

P. Filipowicz, P. Meystre, G. Rempe, and E. H. Walther, Rydberg Atoms, Journal of Modern Optics, vol.32, issue.9, p.1105, 1985.
DOI : 10.1080/713821832

Y. Suematsu, Advances in Semiconductor Lasers, Physics Today, vol.38, issue.5, 1985.
DOI : 10.1063/1.880972

D. Meschede, Centimeter-wave spectroscopy of highly excited rubidium atoms, Journal of the Optical Society of America B, vol.4, issue.3, p.413, 1987.
DOI : 10.1364/JOSAB.4.000413

R. R. Freeman and D. Kleppner, Core polarization and quantum defects in high-angular-momentum states of alkali atoms, Physical Review A, vol.14, issue.5, p.1614, 1976.
DOI : 10.1103/PhysRevA.14.1614

J. R. Rubbmark, M. M. Kash, M. G. Littman, and E. D. Kleppner, Dynamical effects at avoided level crossings: A study of the Landau-Zener effect using Rydberg atoms, Physical Review A, vol.23, issue.6, p.3107, 1981.
DOI : 10.1103/PhysRevA.23.3107

A. Mooradian, Lasers Physics, Systems and Techniques, SUSSP, 1982.

C. E. Wieman and L. Hollberg, Using diode lasers for atomic physics, Review of Scientific Instruments, vol.62, issue.1, p.1, 1991.
DOI : 10.1063/1.1142305

T. W. Ducas, M. G. Littman, R. R. Freeman, and E. D. Kleppner, Stark Ionization of High-Lying States of Sodium, Physical Review Letters, vol.35, issue.6, p.366, 1975.
DOI : 10.1103/PhysRevLett.35.366

H. Kogelnik and T. Li, Laser Beams and Resonators, Proc. IEEE, p.1312, 1966.
DOI : 10.1109/proc.1966.5119

P. Goy, M. Gross, J. M. Raimond, and J. C. Buisson, A Full-coverage 16-250 GHz millimeter scalar network analyzer, Annals of Telecommunications, vol.59, issue.4, p.331, 1988.
DOI : 10.1103/PhysRevLett.59.1899

P. Goy, M. Gross, and E. F. Beck, Transmission-Reflection Measurements from 8 GHz to the THz, 18 th International Conference on IR & mm Waves, 1993.

W. Winkler, R. Schilling, K. Danzmann, J. Mizuno, A. Rüdiger et al., Light scattering described in the mode picture, Applied Optics, vol.33, issue.31, 1994.
DOI : 10.1364/AO.33.007547

J. D. Jackson, Classical Electrodynamics John Wiley & Sons, 1975.

A. A. Abrikosov, L. P. Gor-'kov, and I. M. Khalatnikov, A superconductor in a high frequency field, Sov. Phys. JETP, vol.35, p.182, 1959.

H. Diepers, O. Schmidt, H. Martens, and F. S. Sun, A new method of electropolishing niobium, Physics Letters A, vol.37, issue.2, p.139, 1971.
DOI : 10.1016/0375-9601(71)90095-8

D. J. Heinzen and M. S. Feld, Vacuum Radiative Level Shift and Spontaneous-Emission Linewidth of an Atom in an Optical Resonator, Physical Review Letters, vol.59, issue.23, pp.2623-170, 1987.
DOI : 10.1103/PhysRevLett.59.2623

C. I. Sukenik, M. G. Boshier, D. Cho, V. Sandoghdar, and E. A. Hinds, Measurement of the Casimir-Polder force, Physical Review Letters, vol.70, issue.5, p.560, 1993.
DOI : 10.1103/PhysRevLett.70.560

A. Morinaga, T. Tako, and E. N. Ito, Sensitive measurement of phase shifts due to the ac Stark effect in a Ca optical Ramsey interferometer, Physical Review A, vol.48, issue.2, p.1364, 1993.
DOI : 10.1103/PhysRevA.48.1364

L. Davidovich, A. Maali, M. Brune, J. M. Raimond, and E. S. Haroche, Quantum switches and nonlocal microwave fields, Physical Review Letters, vol.71, issue.15, p.2360, 1993.
DOI : 10.1103/PhysRevLett.71.2360