Are there quantum jumps?

Although Schrödinger eliminated the idea of a quantum jump from the early quantum physics, they reappeared much later again in specific circumstances, after experimental capabilities were advanced enough.

In quantum optics, one routinely observes and analyzes quantum jumps, the most conspicuous experimental demonstrations of collapse. See, e.g.,

or A much-cited paper is (Martin Plenio is Director of the Institute of Theoretical Physics at Ulm University. Peter Knight is a Past-President of the Optical Society of America.)

The Lindblad equations, universally used to describe the dynamics of (mixed) states of open systems have dissipative terms, which are the leftover of collapse when averaged over the quantum jumps.

The 50 page paper

gives a good overview over methods to control single electron spins. ''The experiments show that one or two electrons can be trapped in a quantum dot; that the spin of an individual electron can be put in a superposition of up and down states; that two spins can be made to interact and become entangled in a singlet or triplet state; and that the result of such manipulation can be measured on individual spins.
Quantum jumps of single electrons can be seen, e.g., in FIG. 13. The measured current jumps between that for the two states ''electron in the dot'' (a matastable state reachable by tunneling) and ''no electron in the dot'', being essentially constant in between.

A derivation of quantum jump processes from unitary dynamics of a bigger closed system is given in the paper

In particular, pp.53-58 of this paper describe a fairly elementary derivation of a quantum jump process responsible for photodetection, starting with the unitary dynamics and involving no collapse but only standard approximations from statistical mechanics.
The quantum jump processes for general measurement situations are derived from unitarity in the more technical papers [30-32] by Breuer and Petruccione cited in the paper mentioned above. All four papers can be downloaded from Breuer's web site.

See also the following discussions at PhysicsForums: Collapse from unitarity
Papers on quantum jumps

Arnold Neumaier (
A theoretical physics FAQ