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.,
RG Hulet, DJ Wineland, JC Bergquist, WM Itano,
Precise test of quantum jump theory,
Phys. Rev. A 37, 4544 - 4547 (1988)
or
N Gisin, PL Knight, IC Percival, RC Thompson, and DC Wilson,
Quantum State Diffusion Theory and a Quantum Jump Experiment,
Journal of Modern Optics 40, 1663 (1993)
A much-cited paper is
MB Plenio, PL Knight,
The quantum-jump approach to dissipative dynamics in quantum
optics,
Rev. Mod. Phys. 70, 101 - 144 (1998).
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
R. Hanson et al.,
Spins in few-electron quantum dots,
http://arxiv.org/abs/cond-mat/0610433
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.
Arnold Neumaier (Arnold.Neumaier@univie.ac.at)
A theoretical physics FAQ