We investigate the conditions under which unconditional dense coding can be achieved using continuous-variable entanglement. We consider the effect of entanglement impurity and detector efficiency and discuss experimental verification. We conclude that the requirements for a strong demonstration are not as stringent as previously thought, and are within the reach of present technology.

• Received 15 March 2002

DOI:https://doi.org/10.1103/PhysRevA.66.042321