An atom in the ground state subject to weak illumination will jump up, in an instant, to the excited state at some random time. At least this is a standard description of the process which is at the heart of many light-matter interaction processes.
Dodd Walls theorist Howard Carmichael has shown that this is only an approximation to the true behavior. In fact, if the environment of the atom is monitored carefully enough, quantum jumps are actually a smooth and deterministic process that can be reversed half way through.
Working with an experimental group from Yale University this has been demonstrated experimentally using superconducting qubits as the “atom”.
The results are published in this week’s issue of Nature.