= Nonclassical state of light
A state of light is nonclassical when it is not a <classical mixture of coherent states>. The <Glauber-Sudarshan representation> states this criterion in phase space. Examples include nonvacuum <number states> and <quadrature squeezing> states. A <coherent state> is on the classical boundary despite its <vacuum fluctuations>; <thermal light> is a classical mixture despite its non-Poisson fluctuations. None of these <nonclassicality witnesses> is a necessary condition for nonclassicality.
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