The Fock state (e.g. a single photon) is the most particle-like state; it has a fixed number of particles, and phase is indeterminate.

It should be noted that the notation | \alpha \rangle does not refer to a Fock state. For example, at \alpha = 1, one should not mistake |1 \rangle as a single-photon Fock state — it represents a Poisson distribution of fixed number states with a mean photon number of unity.

— Wikipedia on Coherent state

2009.12.10 Thursday ACHK