Coherent propagation and quantum beats of quadrupole polaritons in Cu2O

Abstract Coherent propagation of quadrupole polaritons in Cu 2 O is demonstrated by time resolved spectroscopy. Clearly resolved oscillations with time-dependent period are observed. The experimental results are quantitatively explained as resulting from quantum beats between the two branches of the exciton-polariton. The analysis yields the homogeneous line width of 6.5x10 −7 eV and an oscillator strength of f =3.6x10 −9 . Measurements at intensities higher than 10 8 W/cm 2 lead to faster decay and a clear reduction of the beat amplitude.