How Quick Is a Quantum Jump?

Although the only time scale one ordinarily associates with a quantum transition is its lifetime, observations of “quantum jumps” in recent years show that the actual transition time is much shorter. I define a “jump time” as the time scale such that perturbations occurring at intervals of this duration affect the decay. In terms of the “Zeno time” (related to the second moment of the Hamiltonian) the jump time is τJ ≡ τ2 Z /τL . Corroboration is given. I also show that observing the “jumping” will not seriously affect the system lifetime, but will affect the linewidth. This is consistent with Bohr’s ideas on measurement as well as with a heuristic time-energy uncertainty principle.