A continuous variable quantum key distribution system comprises a transmitter and a receiver. The first quantum signal has a first polarization and is associated with first quadrature components and the second quantum signal has a second polarization and is associated with second quadrature components. The receiver receives the quantum signals transmitted by the transmitter via a quantum communication channel; estimates a channel matrix representing the polarization rotation of the first and second polarization caused by the quantum communication channel; modifies the received first and second quantum signals on the basis of the polarization rotation; and uses the modified received first and second quantum signals for generating a secret key. The transmitter may modify the transmitted first quantum signal and the transmitted second quantum signal based on the polarization rotation and use the modified transmitted first quantum signal and the modified transmitted second quantum signal for generating a secret key.