We perform a proof-of-principle demonstration of the measurement-device-independent quantum key distribution (MDI-QKD) protocol using weak coherent states and polarization-encoded qubits over two optical fiber links of 8.5 km each. Each link was independently stabilized against polarization drifts using a full-polarization control system employing two wavelength-multiplexed control channels. A linear-optics-based polarization Bell-state analyzer was built into the intermediate station, Charlie, which is connected to both Alice and Bob via the optical fiber links.Using decoy-states, a lower bound for the secret-key generation rate of 1.04  10 -6 bits/pulse is computed.

A real-time polarization control system employing two non-orthogonal reference signals multiplexed in either time or wavelength with the data signal is presented. It is shown, theoretically and experimentally, that complete control of multiple polarization states can be attained employing polarization controllers in closed-loop configuration. Experimental results on the wavelength multiplexing setup show that negligible added penalties, corresponding to an average added optical Quantum Bit Error Rate of 0.044%, can be achieved with response times smaller than 10 ms, without significant introduction of noise counts in the quantum channel.

Remote Laboratories have become part of current teaching and learning, particularly in engineering. Their potential to aid students beyond their hands-on lab classes has been a matter of discussion in literature. Teachers and researchers are aware that the thorough analysis of both strengths and shortcomings of remote labs in didactical implementations may not only lead to the improvement of these resources but also of the pedagogical implications in engineering classes. The present study was carried out in a Higher Education Institution in Brazil in two different courses during three consecutive semesters where a remote lab (VISIR) addressing electric and electronic topics was implemented, yielding 471 students' academic results and opinions. These students' results (while using VISIR) cross-analysed with the course characteristics, reveal some factors teachers may tackle to foster student learning and motivation. The conclusions point to the need for VISIR interface modernization and showed it is more useful in basic courses than in more advanced ones, when dealing with classic lab experiments. Results also show that teachers' involvement plus their ability to brief students on VISIR's usefulness have a significant influence not only on students' performance but also on their perception of learning and satisfaction with the tool. In the analysed cases, the students with more learning needs seemed to be the ones who could benefit more from VISIR.

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 setup 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 40 π rad/s are effectively compensated. We demonstrate that our setup 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.

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