Photon Statistics of the Linear Amplifier
The linear light amplifier has recently generated renewed discussion in connection with the question whether it is possible to reproduce or clone an incident photon in an arbitrary quantum state. [l–3] If exact cloning were possible, this would imply a violation of the uncertainty principle, so that some fundamental limitations are imposed on the amplifier. The same limitations prevent light amplifiers, when inserted into one or more arms of an interferometer, from allowing us to determine which path through the interferometer a given photon followed. What prevents precise cloning of a photon is the existence of spontaneous and unpredictable photon emissions in any amplification mechanism,[2,3] so that there is only a stochastic connection between the incoming and outgoing photons. This is the subject of the present article.
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