  Protocols used in quantum information and precision spectroscopy rely on
efficient internal quantum state discrimination. With a single ion in a linear
Paul trap, we implement a novel detection method which utilizes correlations
between two detection events with an intermediate spin-flip. The technique is
experimentally characterized as more robust against fluctuations in detection
laser power compared to conventionally implemented methods. Furthermore,
systematic detection errors which limit the Rabi oscillation contrast in
conventional methods are overcome.
