  We describe and experimentally demonstrate a three-party quantum secret
sharing protocol using polarization-entangled photon pairs. The source itself
serves as an active participant and can switch between the required photon
states by modulating the pump beam only, thereby making the protocol less
susceptible to loss and amenable to fast switching. Compared to three-photon
protocols, the practical efficiency is dramatically improved as there is no
need to generate, transmit, or detect a third photon.
