/ 04 09 19 1 v 2 10 F eb 2 00 5 Proposed experiment for the quantum “ Guess My Number ” protocol

An experimental realization of the entanglement-assisted “Guess My Number” protocol for the reduction of communication complexity, introduced by Steane and van Dam, would require producing and detecting three-qubit GHZ states with an efficiency η > 0.70, which would require single photon detectors of efficiency σ > 0.89. We propose a modification of the protocol which can be translated into a real experiment using present-day technology. In the proposed experiment, the quantum reduction of the multiparty communication complexity would require an efficiency η > 0.05, achievable with detectors of σ > 0.47, for four parties, and η > 0.17 (σ > 0.55) for three parties.