  While the phenomenon of the exact crossing of energy levels is a rarely
occurring event, in the case of quantum resonances associated with metastable
states this phenomenon is much more frequent and various scenarios can occur.
When there is an exact crossing of the imaginary parts of the resonances in a
two-level quantum system subject to an external DC electric field, then a
damped beating phenomenon occurs, which is absent if there is no such crossing.
This fact, tested numerically on an explicit one-dimensional model, suggests
the possibility of designing quantum sensors to determine in a very simple way
whether the external field strength has an assigned value or not.
