Even during hard lock-down times, when researchers may have reduced access to their labs, the quantum progress should go on. An option to conduct quantum experiments from home is provided by simulation tools like VPItransmissionMaker Optical Systems & VPItoolkit QKD (https://www.vpiphotonics.com/Tools/QKD/). Based on a solid modeling approach, we can simulate complex optical systems for QKD applications, such as this polarization-encoded BB84 protocol with polarization drift compensation.
On Alice’s side, a sequence of pulses with orthogonal polarization is sent through a quantum channel. During propagation in a fiber, the polarization state may slowly drift over time due to polarization mode dispersion (PMD), which leads to an increase of QBER. On Bob’s side, a polarization controller monitors QBER. When the error rate exceeds the predefined threshold, quantum communication between Alice and Bob is stopped and compensation of the polarization drift starts. First, the module performs arbitrary polarization rotations and measures the resulting QBERs. Using the measured data, the reverse polarization transform is calculated and applied to mitigate the PMD. Now, Alice and Bob can continue their quantum communication again.