Nonclassical correlations of photon number and field components in the vacuum state
Holger Friedrich Hofmann, Takayoshi Kobayashi, Akira Furusawa · Physical Review A · 2000
It is shown that the quantum jumps in the photon number $\mathrm{n\ifmmode \hat{}\else \^{}\fi{}}$ from zero to one or more photons induced by backaction evasion quantum nondemolition measurements of a quadrature component $◯$ of the vacuum light field state are strongly correlated with the quadrature component measurement results. This correlation corresponds to the operator expectation value $〈◯\mathrm{n\ifmmode \hat{}\else \^{}\fi{}}◯〉$ which is equal to one-fourth for the vacuum even though the photon number eigenvalue is zero. Quantum nondemolition measurements of a quadrature component can thus provide experimental evidence of the nonclassical operator ordering dependence of the correlations between photon number and field components in the vacuum state.