Quantum interference by femtosecond multi-photon absorption in conjugated dendrimers

We demonstrate high contrast interference fringes when near-IR frequencies and UV frequency 3ω excite fluorescence via two alternative but in practice indistinguishable quantum pathways. We use specially synthesized organic dendrimers with an exceptionally large three-photon cross section, σ3=1.5 10-79 cm6 s2 based on bisdiphenylamino stilbene core and bis-diphenylamino di-styryl benzene repeat units. We show for the first time that quantum interference signal can be strong enough for being observed with an unaided eye.