Continuous-variable quantum teleportation through lossy channels

The ultimate limits of continuous-variable single-mode quantum teleportation due to absorption are studied, with special emphasis on (quasi-)monochromatic optical fields propagating through fibers. It is shown that even if an infinitely squeezed two-mode squeezed vacuum were used, the amount of information that would be transferred quantum mechanically over a finite distance is limited and effectively approaches to zero on a length scale that is much shorter than the (classical) absorption length. Only for short distances the state-dependent teleportation fidelity can be close to unity. To realize the largest possibly fidelity, an asymmetrical equipment must be used, where the source of the two-mode squeezed vacuum is nearer to Alice than to Bob and in consequence the coherent displacement performed by Bob cannot be chosen independently of the transmission lengths.