  We present the first experimental realization of a flexible multidimensional
quantum channel where the Hilbert space dimensionality can be controlled
electronically. Using electro-optical modulators (EOM) and narrow-band optical
filters, quantum information is encoded and decoded in the temporal degrees of
freedom of photons from a long-coherence-time single-photon source. Our results
demonstrate the feasibility of a generic scheme for encoding and transmitting
multidimensional quantum information over the existing fiber-optical
telecommunications infrastructure.
