In physics and chemistry, an atomic electron(ic) transition (could be simply called an atomic transition, a quantum jump, or quantum leap) is a change of an electron from one quantum state to another within an atom[1] (or artificial atom[2]). It appears to be discontinuous (observed for example in fluorescence signal of another transition as burst noise); the electron "jumps" from one energy level to another very quickly (transition time often in a few ns or less). Quantum leaps cause the emission (or absorption) of electromagnetic radiation, including that of light, which occurs in the form of quantized units called photons. Their statistics is Poissonian and the damping of statistic values of time between jumps is exponential (in average).[3] The damping time constant (ranges from nanoseconds to a few seconds) relates to the natural, pressure and field broadening of spectral lines.
Although changes of quantum state occur on the submicroscopic level, in popular discourse, the term "quantum leap" refers to a large increase (Oxford English Dictionary).