Entanglement death and purity loss forever in the dispersive interaction of a trapped ion and light without energy relaxation

Death of entanglement between light and the vibrational motion of a single trapped ion in the dispersive regime with a reservoir is investigated. It is found that with phase-damped cavity, the purity of the light-motional states is lost forever, unlike the purity of the ion's internal states which have regular patterns and they do not decay. The asymptotic behavior of the states of the light, the ion-motional and the total system fall into a mixed state. The entanglement and purity have strong sensitivity to the phase damping and the ionic distribution angle. The entanglement sudden death has been treated as it arises from the effect of phase damping on mixed as well as pure states.