Quantum jump and continuous measurement in multi-level atom

In this paper we investigate the quantum jump in a multi-level atom and con struct a formal solution to the optical Block equation describing the inter action system of the multi-level atom with incident resonant laser. It is p roved that pure state analysis theory is no longer applicable to a multi-le vel atom system, so a mixed one is developed, concluding that the resetting density of a multi-level atom should be described by mixed state analysis theory. We also discuss the continuous quantum measurement along with quant um jumping in a multi-level atom.