Abstract
In this paper we demonstrate an active polarization drift compensation scheme for optical fibres employed in a quantum key distribution experiment with polarization encoded qubits. The quantum signals are wavelength multiplexed in one fibre along with two classical optical side channels that provide the control information for the polarization compensation scheme. This set-up allows us to continuously track any polarization change without the need to interrupt the key exchange. The results obtained show that fast polarization rotations of the order of 40π rad s−1 are effectively compensated for. We demonstrate that our set-up allows continuous quantum key distribution even in a fibre stressed by random polarization fluctuations. Our results pave the way for Bell-state measurements using only linear optics with parties separated by long-distance optical fibres.
Highlights
Quantum Key Distribution (QKD) [1] was first experimentally demonstrated with polarization encoded photons sent over a free-space distance of 30 cm [2]
We demonstrate an active polarization drift compensation scheme for optical fibres employed in a quantum key distribution experiment with polarization encoded qubits
It is a well-known phenomenon in classical optical communications that residual fibre birefringence modifies the State of Polarization (SOP) of a signal propagating along the fibre
Summary
Quantum Key Distribution (QKD) [1] was first experimentally demonstrated with polarization encoded photons sent over a free-space distance of 30 cm [2]. Active polarization control schemes for quantum communication have been successfully implemented to distribute polarization encoded qubits over optical fibres [11, 12] In both cases, the QKD session was interrupted at times to perform the polarization tracking. A real time polarization control scheme, able to track all polarization states at the receiver end is of great interest for QKD and for other applications, such as partial long-distance Bell state measurements employing linear optics [15] and quantum relays and repeaters [16, 17] Such a control scheme was recently realized using two ITU-T (International Telecommunication Union Telecommunication Standardization Sector) standard grid side channels adjacent to the quantum signal wavelength in order to provide the necessary classical feedback to the control loop [18]. The whole experiment is performed using only off-the-shelf standard telecom components, making it a practical implementation to be used in future polarization encoded quantum communication experiments
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