Spontaneous emission cannot be explained by classical electromagnetic theory and is fundamentally a quantum process. According to the American Physical Society, the first person to correctly predict the phenomenon of spontaneous emission was Albert Einstein in a series of papers starting in 1916, culminating in what is now called the Einstein A Coefficient. Einstein's quantum theory of radiation anticipated ideas later expressed in quantum electrodynamics and quantum optics by several decades. Later, after the formal discovery of quantum mechanics in 1926, the rate of spontaneous emission was accurately described from first principles by Dirac in his quantum theory of radiation, the precursor to the theory which he later called quantum electrodynamics. Contemporary physicists, when asked to give a physical explanation for spontaneous emission, generally invoke the zero-point energy of the electromagnetic field. In 1963, the Jaynes–Cummings model was developed describing the system of a two-level atom interacting with a quantized field mode (i.e. the vacuum) within an optical cavity. It gave the nonintuitive prediction that the rate of spontaneous emission could be controlled depending on the boundary conditions of the surrounding vacuum field. These experiments gave rise to cavity quantum electrodynamics (CQED), the study of effects of mirrors and cavities on radiative corrections.