Practical considerations for detection of squeezed light

This thesis investigates the generation and detection of squeezed light with a focus on mitigating state of polarization (SOP) mismatch between squeezed light and local oscillator (LO) field. The consequence of this mismatch is a lowered measured squeezing level. A polarisation control system was implemented to mitigate this effect and two algorithms for automated feedback control were examined: parallel gradient descent (PGD) and particle swarm algorithm (PSA). In stable operating conditions, PGD performed better with an average convergence time of 33±7.7 seconds. In comparison PSA tended to have a slower convergence of 64 ±28 seconds in stable conditions, but proved more resilient to unstable operating conditions. By implementing polarisation control into our squeezing setup, the squeezing efficiency improved by 50% and a decrease of 83% in standard deviation between measurements was observed. The scheme also has applications in the NQCIS infrastructure where a similar drifting polarisation state leads to a lowered quantum key transmission rate.