Quantum information exchange employing optics

Quantum communication is a future technology that can provide fabulous functions. The most promising medium for realizing quantum communication is thought to be a combination of a weak laser pulse and an optical fiber. However, due to the actual loss in the optical fiber, there must be an upper limit to the quantum communication performance when we use this medium. The main contributions of all the existing theoretical researches with respect to the performance when we use this medium have been proposals of new quantum protocols with better performance than before. We give the theoretical limit of the performance by rigorously evaluating the trade-off between the quality of entanglement and the probability of success. This result reveals the capability of the existing scheme and will contribute to progress on quantum communication technology.