Errors in “the sifted” quantum key while transmissing via single-mode stochastic anisotropic inhomogeneous fiber

In this article we take into consideration time dynamics of a field density matrix in basis of conditions of vacuum and two orthogonal polarization photons. The analysis was performed using the device with passive modulation of distributed photons conditions and additional unexcited modes. Errors in the sifted key can appear due to the absorption and depolarization of photons, as well as from the optical fibre (ОВ) parameters disorder. We find the average relative error (QBER) for variation of OB parameters in the sifted quantum key using BB84 protocol distribution with polarizing coding of the information. It is possible to reduce QBER significantly, even when random ОВ parameters are widely dispersed. For identifying the protocol working conditions at large distances we use the polarizing palpation effect, most clearly expressed when average value of OB parameters surpass their variation. In conclusion, the correct choice of OB manufacturing technology will lower QBER to the critical level of 0.11, below which the distributed key can be applied for cryptographical purposes.