  The electron signals from the field ionization of two closely-spaced Rydberg
states of \mbox{rubidium-85} are separated using quantum control. In selective
field ionization, the state distribution of a collection of Rydberg atoms is
measured by ionizing the atoms with a ramped electric field. Generally, atoms
in higher energy states ionize at lower fields, so ionized electrons which are
detected earlier in time can be correlated with higher energy Rydberg states.
However, the resolution of this technique is limited by the Stark effect. As
the electric field is increased, the electron encounters numerous avoided Stark
level crossings which split the amplitude among many states, thus broadening
the time-resolved ionization signal. Previously, a genetic algorithm has been
used to control the signal shape of a single Rydberg state. The present work
extends this technique to separate the signals from the $34s$ and $33p$ states
of rubidium-85, which are overlapped when using a simple field ramp as in
selective field ionization.
