No abstract

According to relativity, the reading of an ideal clock is interpreted as the elapsed proper time along its single classical trajectory. In contrast, quantum theory allows the association of many simultaneous paths with a single quantum clock. Here, we investigate how the superposition principle affects the gravitational time dilation observed by a simple clock-a decaying two-level atom. Placing such an atom in a superposition of positions enables us to analyze a quantum contribution to a classical time dilation, manifested in the process of spontaneous emission. In particular, we show that the emission rate of an atom prepared in a coherent superposition of separated wave packets in a gravitational field is different from the transition rate of the atom in a classical mixture of these packets, which gives rise to a nonclassical-gravitational time dilation effect. In addition, we show the effect of spatial coherence on the atom's emission spectrum.