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Polarization based discrete variables quantum key distribution via conjugated homodyne detection

Ramos, M. F. ; Pinto, A. N. ; Silva, N. A.

Scientific Reports Vol. 12, Nº 1, pp. 1 - 13, April, 2022.

ISSN (print): 2045-2322
ISSN (online):

Scimago Journal Ranking: 1,24 (in 2020)

Digital Object Identifier: 10.1038/s41598-022-10181-4

Optical homodyne detection is widely adopted in continuous-variable quantum key distribution for
high-rate field measurement quadratures. Besides that, those detection schemes have been being
implemented for single-photon statistics characterization in the field of quantum tomography. In
this work, we propose a discrete-variable quantum key distribution (DV-QKD) implementation that
combines the use of phase modulators for high-speed state of polarization (SOP) generation, with a
conjugate homodyne detection scheme which enables the deployment of high speed QKD systems.
The channel discretization relies on the application of a detection threshold that allows to map the
measured voltages as a click or no-click. Our scheme relies also on the use of a time-multiplexed pilot
tone—quantum signal architecture which enables the use of a Bob locally generated local oscillator
and opens the door to an effective polarization drift compensation scheme. Besides that, our results
shows that for higher detection threshold values we obtain a very low quantum bit error rate (QBER)
on the sifted key. Nevertheless, due to huge number of discarded qubits the obtained secure key
length abruptly decreases. From our results, we observe that optimizing the detection threshold
and considering a system operating at 500 MHz symbol generation clock, a secure key rate of
approximately 46.9 Mbps, with a sifted QBER of 1.5% over 40 km of optical fiber. This considering the
error correction and privacy amplification steps necessary to obtain a final secure key.