  We introduce a general mapping for encoding quantum communication protocols
involving pure states of multiple qubits, unitary transformations, and
projective measurements into another set of protocols that employ coherent
states of light in a superposition of optical modes, linear optics
transformations and measurements with single-photon threshold detectors. This
provides a general framework for transforming protocols in quantum
communication into a form in which they can be implemented with current
technology. We explore the similarity between properties of the original qubit
protocols and the coherent-state protocols obtained from the mapping and make
use of the mapping to construct new protocols in the context of quantum
communication complexity and quantum digital signatures. Our results have the
potential of bringing a wide class of quantum communication protocols closer to
their experimental demonstration.
