Physical Review LettersQuantum beats in photon echo from four-waving mixingXuejun Zhu, Mark S. Hybertsen, P. B. LittlewoodPublished Jul 4, 1994• 9 citationsPublisherAbstractA Comment on the Letter by M. Koch et al., Phys. Rev. Lett. 69, 3631 (1992).Received 14 February 1994DOI:https://doi.org/10.1103/PhysRevLett.73.209©1994 American Physical SocietyDOI10.1103/physrevlett.73.209