Quantum Optics IV pp 188-199 | Cite as

# First Order Coherence of Vacuum Fluctuations: Optical Pumping Experiments in Presence of Electromagnetic Boundaries

## Abstract

The existence of 0-point fluctuations of any field, and in particular of the electromagnetic one, can be taken as a semantic boundary between the realms of classical and quantum physics (1, 2). It seems therefore important to investigate, by simple and noncontroversial experiments, the properties of physical systems which are believed to be substantially affected by its presence. In electrodynamics the famous Casimir experiments belong to this class. In the present work the spontaneous emission (SE) of optical radiation from excited atoms is taken as test process of the underlying quantum fluctuations associated with radiation states with zero or, maximum, one photon per mode. Of course the causal correspondence between SE (or Lamb shift (LS)) effects and field fluctuations has been questioned by several authors in the last years (3–7). In these works radiation-reaction has been assumed as an alternative model allowed by the commutation properties of atomic- and field-operators in the Heisenberg theory of quantized atom-radiation interaction. However we believe that the problem has in fact been recently and definitely solved by theorists of the Ecole Normale Superieure in Paris, in favor of the correspondence Spontaneous Emission-Vacuum Field on the grounds of the operator hermiticity that should necessarily correspond to the separate obvervability of the time rates of change of any atomic operator interacting respectively with vacuum and radiation-reaction fields (8). This leads to favor, among possible operator-ordering procedures in the nondifferential part of the Heisenberg equation, the completely symmetric one. The soundness of this interpretation can be satisfactorily taken as the basis of our model, which could be also recast pictorially in the following way: Spontaneously emitted (or scattered) photons on a field mode k can be considered as “stimulated” by the 0-point field existing in that mode.

### Keywords

Microwave Coherence Ruby Flint Peaked## Preview

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### References

- 1.C. Itzykson, J. B. Zuber: Quantum Field Theory (Mc-Graw Hill, New York 1980) Ch 11. For Casimir effect: Ch 3. H. Casimir, D. Polder;Phys. Rev. 73, 360 (1948).Google Scholar
- 2.J. A. Wheeler, W. Zurek: Quantum Theory and Measurement (Princeton University, 1983 )Google Scholar
- 3.A. O. Barut (Editor): Foundations of Radiation Theory and Quantum Electrodynamics (Plenum, New York, 1980 ). Cfr. papers by P. W. Milonni, J. H. Eberly, K. Wodkiewich. A survey of Stochastic Electrodynamics is given by T. H. Boyer.Google Scholar
- 4.J. R. Ackerahlt, P. L. Knight, J. H. Eberly: Phys. Rev. Letts. 30, 456 (1973) and Phys. Rev. D 10, 3350 (1974).ADSGoogle Scholar
- 5.P. W. Milonni; Optics Comm. 9, 119 (1973) (with P. L. Knight); Phys. Rep. 31, 955 (1976)Google Scholar
- 6.M. R. Philpott: Chem. Phys. Lett. 19, 435 (1973);see also H. Morawitz, Phys. Rev. 187, 1792 (1969). In Philpott paper a sign mistake in expression (13) corresponding to our (4’), case 2, leads to an incorrect statement in the discussion of the result of the same equation.ADSCrossRefGoogle Scholar
- 7.I. R. Senitzky: Phys. Rev. Lett. 31, 955 (1973).ADSCrossRefGoogle Scholar
- 8.J. Dalibard, J. Dupont-Roc and C. Cohen Tannoudij: J. Phys. 43 1617 (1982). For QED with Lippman fringes see E. Fermi, Rev. Mod. Physics 4, 87 (1932) and. S. Agarwal Phys. Rev. A 12, 1987 (1975).Google Scholar
- 9.M. Born and E. Wolf: Principles of Opticss (Macmillan, New York, 1980) For interference and Fabry-Perot interferometry: Ch. VII. O. Wiener: Ann. d. Physik, 40, 203 (1890). A Wiener technique was used to study transfer of electron excitation in solids by P. Liao, H. Weber and B. Tofield, Solid State Comm. 16, 881 (1975).Google Scholar
- 10.SE lifetimes T by molecular monolayers close to single metal surfaces have been investigated by the Goettingen group: cfr. for a comprehensive covering of the subject and bibliography the review paper by K. K. Drexhage in Progress in Optics, North-Holland, Amsterdam, 1974. Vol. XII. That work is connected with the present one. However cavity effects, intensity effects on radiation pattern collective effects from a thick medium as well as the Wiener pumping technique we are reporting here have not been previously studied or anticipated. Owing to the large number of radiation modes which determine T with very limited mode discrimination close to a single conducting surface, this one affects T only over a small distance of order A. In order to interpret the Goettingen results, which seem not to have been reproduced elsewhere (likely, because of the difficulty of the monolayer technique), a large amount of interesting theoretical work, mostly based on classical arguments, has been produced in the past. Among the heuristic models proposed: effeet of boundaries on antenna impedance and dipole-image interaction. This last model has also been treated using field quantization as a kind of superradiant effeet. However, apart from the “image” concept that seems to be irrelevant, by definition, in reality consideration, this model, when translated into quantum theory corresponds to the atomic “self-reaction” process which is ruled out by the rigorous quantum mechanical considerations of Ref. 8. So far, the vacuum field interpretation has not been explicitly proposed to explain the Goettingen results. Our work on cavity effects is connected with the following publications: D. Kleppner, Phys. Rev. Lett. 47, 223, 1981; 55, 2137, 1985 (with R. G. Hulet, E. S. Hilfer); P. Goy, J. L. Raymond, M. Gross and S. Haroche, Phys. Rev. Lett. 50, 1903, 1983; D. Meschede, H. Walther and G. Muller, Phys. Rev. Lett. 54, 551, 1985. Note that, dealing with optical spectra (h
*v*<< kT) allows us to work at room-T.Google Scholar - 11.W. Koechner; Solid State Engineering (Springer-Verlag, Berlin, 1976 ). Pumping bands emission lines and refractive indexes of ruby are given in Ch. 2.Google Scholar
- 12.F. E. Terman; Electronic and Radio Engineering (McGraw-Hill, New York, 1955). Ch 23.Google Scholar
- 13.R. J. Glauber, Phys. Rev. 131, 2766 (1963); R. Loudon; The Quantum Theory of Light (Oxford, 1983). Ch. 5.MathSciNetADSCrossRefGoogle Scholar
- 14.The conceptual indirectness of QED has been pointed out by many leading scientists in the past. See for instance: R. P. Feynmann;The Quantum Theory of Fields, Interscience, New York, 1961;V. F. Weisskopf, Physics of Twentieth Century M. I. T. Press, Cambridge, 1972 and our Ref. 4. Nevertheless we believe that in the particular context of the processes we investigate in the present paper, the explanation based on vacuum-fluctuations has a direct and simple correspondence with its description given by QED. This doesnft seem the case for other “heuristic” interpretations we refer to in (10). To our knowledge no interpretation other than vacuum-fluctuations has been proposed so far forthe Casimir effect. This one has been experimentally tested many times (1). This seems to be sufficient for concluding in favor of a real existence of the vacuum field whatever definition of “reality” we decide to adopt.Google Scholar