Dear Editor,

please find enclosed a manuscript on an experiment for finding an upper bound
for a possible time scale for a quantum jump, based on photon pairs emerging
from a cascade decay in an atomic system.

The methods involved so far to curb the time scale of seemingly
instantaneous transitions, starting with Dehmelt's electron shelving
proposal in 1975, involved waiting time analysis in a telegraph signal
monitoring a quantum system.

In our work, we present a different method, where we monitor the state
information of an atomic system through the timing correlation of a photon
pair with a well-defined time ordering. This permits a relatively simple
method for putting an upper bound to any possible dynamics involved in a
quantum jump, should there be one. With fairly standard single photon
detectors, we don't observe any dynamics (which is perhaps not too
surprising), but find a bound for a time scale of a possible dynamics which is
about 3 orders of magnitude shorted than the typical lifetimes for
participating excited states in atoms. 

This method is likely to improve the time resolution at least an order of
magnitude with more advanced photodetectors, or possibly other physical
systems with similar cascade-like decays.

We feel that the simplicity of our method and the relatively tight bound we
obtain in a first experiment would make Physical Review Letters an adequate
platform to reach out to a large physics community (and beyond) with a broad
awareness of the quantum jump concept, and look forward for your consideration
to publish this manuscript.

With Best Regards on behalf of all authors,

Christian Kurtsiefer


Why PRL


Since the early days of quantum physics, the seemingly instantaneous
transitions in quantum physics, or quantum jumps, have plagued physicists, and
remain a challenge in the interpretation of measurements on quantum systems.
We present a simple method and experiment to bound the time scale of a possible
jump dynamics in an atomic system which is based on observing
photocorrelations in a cascade decay. This method is fundamentally different
to previous methods analyzing the waiting time statistics in telegraph-like
signatures of quantum jumps, and provides a tight bound compatible with the
time resolution of photodetectors.