  We report Ramsey interference in the excitonic population of a negatively
charged quantum dot revealing the coherence of the state in the limit where
radiative decay is dominant. Our experiments show that the decay time of the
Ramsey interference is limited by the spectral width of the transition.
Applying a vertical magnetic field induces Zeeman split transitions that can be
addressed by changing the laser detuning to reveal 2, 3 and 4 level system
behaviour. We show that under finite field the phase-sensitive control of two
optical pulses from a single laser can be used to prepare both population and
spin qubits simultaneously.
