Quantum coherence in a single ion due to strong excitation of a metastable transition
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We consider pump-probe spectroscopy of a single ion with a highly metastable (probe) clock transition that is monitored by using the quantum jump technique. For a weak clock laser, we obtain the well-known Autler-Townes splitting. For stronger powers of the clock laser, we demonstrate the transition to a new regime. The two regimes are distinguished by the transition of two complex eigenvalues to purely imaginary ones, which can be very different in magnitude. The transition is controlled by the power of the clock laser. For pump on resonance, we present simple analytical expressions for various linewidths and line positions. 2000 The American Physical Society.