Electromagnetic radiation in a cavity with a time-dependent mirror

The quantum radiation field inside a double cavity is examined. The double cavity consists of a cavity containing a reflecting mirror. Two independent radiation fields are present inside the cavity. It is then assumed that the mirror becomes suddenly transparent. The double cavity transforms thus into a single cavity. The relationship between the radiation fields before and after the change is investigated. It is shown that the sudden change excites the radiation modes of the single cavity. Only modes having a node at the position of the mirror are not excited. The sudden change of the mirror’s reflectivity can thus generate photons from the vacuum. It is also shown that the sudden change produces squeezing. These features of the double cavity are then employed in a gedankenexperiment for the generation of entanglement between noninteracting atoms with the quantum eraser technique.