TITLE:
Testing of the Entangled QKD System EPR S405 Quelle (AIT) in Commercial 1550 nm Fiber Network
AUTHORS:
Damian Melniczuk, Monika Jacak
KEYWORDS:
QKD; Entagled System; QBER
JOURNAL NAME:
International Journal of Communications, Network and System Sciences,
Vol.7 No.1,
January
16,
2014
ABSTRACT: In this communication, we report results
of running tests on standard telecommunication metropolitan network 1550 nm
fiber applied to a quantum channel to EPR S405 Quelle prototype systems installed in
National Laboratory for Quantum Technologies WUT and in CompSecur Wroclaw.
Testing was carried out by means of the original design by us and applied special data card collecting
parameters of functioning system allowing for assessment of quality of quantum
channel. We have performed several trials using various configurations of standard
1550 nm fiber patch-cord up to length of 6.5 km with additional usage of
various patch-cords with weldings and connectors which typically
present in already installed commercial metropolitan communication networks.
The implementation of this testing indicated that the rigorous
maintenance of photon polarization is required for quantum information exchange
upon EPR S405 Quelle functioning. The polarization of optical signal turned out to be,
however, very unstable for the tested connection which resulted in very rapid
QBER rise precluding practical usefulness of this connection for secure quantum
exchange of cryptographic key over practically significant distances. We have
identified that the main obstacle was the polarization decoherence caused by
weldings and connectors in standard patch-cords and accidental strains in
fibers as well as generally poor transmitting properties of 1550 nm fiber for
much shorter wave-length photons used by the Quelle system. To maintain the
quantum channel active, very frequent manual corrections of polarization
control were required. So we expect that by design and application of an automatic
polarization control module, one would stabilize visibility ratio and lower
QBER to an acceptable level conditioning possible future implementation of
entangled QKD system in commercial networks.