First Order Coherence of Vacuum Fluctuations: Optical Pumping Experiments in Presence of Electromagnetic Boundaries
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.
KeywordsSpontaneous Emission Pump Beam Excited Atom Lamb Shift Heisenberg Equation
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