QUANTUM DESCRIPTION OF THE BEAM SPLITTER.
Conference Paper
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abstract
The action of a lossless plane-parallel beam splitter on an incident light beam can be described in purely quantum-mechanical terms. Such a description may be obtained in terms of a unitary transformation that connects the incoming radiation-field operator to the outgoing one. This transformation, which is derived and discussed, provides an elegant means to address issues and concepts that are intrinsically quantum-mechanical. One such concept discussed by the authors is that of splitting and coupling of photon states, particularly when neither the phase nor the photon number of the incoming field is well defined. How a beam splitter alters the correlation of noise and fluctuations in two modes that it couples is also discussed. This may have much relevance to an accurate quantitative study of quantum-noise limitations on interferometric measurements of extremely weak signals, e. g. , gravitation waves and tiny rotations. Several examples illustrating these concepts are presented. The unitary description of a beam splitter may also provide a convenient formalism in which to describe laser resonator losses through partially transmitting mirrors in a fully quantum-mechanical way.
