Comment on “Manipulating the frequency-entangled states by an acoustic-optical modulator”

A recent theoretical paper by Shi et al. [Phys. Rev. A 61, 064102 (2000)] proposes a scheme for entanglement swapping utilizing acousto-optic modulators without requiring a Bell-state measurement. In this Comment, we show that the proposal is flawed and no entanglement swapping can occur without measurement.