Quantum interference in the absorption and emission of single photons by   a single ion
  We investigate quantum beats in the arrival-time distribution of single photons from a single trapped $^{40}$Ca$^+$ ion, revealing their fundamentally different physical origins in two distinct experimental situations: In a $\Lambda$-type level scheme the interference of two 854-nm absorption amplitudes suppresses and enhances the emission process of Raman-scattered 393-nm photons; in a V-type level scheme the interference of two 393-nm emission amplitudes causes a rotation of their dipole emission pattern resulting in a temporal modulation of the detected photons. For both cases we demonstrate coherent control over the quantum-beat phase through the phases of the atomic and photonic input states, which also allows controlled adjustment of the total photon detection efficiency. 
Michael Schug, Christoph Kurz, Pascal Eich, Jan Huwer, Philipp   M\"uller, J\"urgen Eschner
quant-ph physics.atom-ph