Improving the state selectivity of field ionization with quantum control

TL;DR

This paper demonstrates how quantum control techniques can improve the resolution of state selectivity in field ionization of Rydberg atoms, enabling better separation of closely spaced energy states.

Contribution

The work extends quantum control methods to enhance the selectivity of field ionization, specifically separating signals from overlapping Rydberg states in rubidium-85.

Findings

Successfully separated signals from 34s and 33p Rydberg states

Extended genetic algorithm control to multiple states

Improved resolution beyond simple field ramp methods

Abstract

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.