# I Randomised phase of laser

1. Mar 17, 2016

### kaje

Hi,
What does it mean when we say that the in the case of absence of a phase reference, the laser would produce a Poissonian mixture of number states?.. I got confused actually between the meaning of the phase in classical sense and quantum in this regard. Regards

2. Mar 21, 2016

### DrDu

The quantum state $|\psi\rangle= c_0|0\rangle+c_1 |1 \rangle +c_2|2\rangle \ldots$ is a superposition of number states.
If the square of the coefficients $|c_i|^2$ follows a Poisson distribution and $c_{n+1}/c_n \sim \exp(i\phi)$, then this state is a coherent state with phase $\phi$ which is as close as you can get in QM to a classical state.