Phase stabilization of high-bandwidth squeezed and entangled states over 1km distributed optical fiber

Quantum Key Distribution (QKD) is a technology for secure communication between two parties, using the principles of quantum mechanics. Our continuous-variable QKD experiment implements a fiber-based scheme connecting two laboratories in two separated buildings (building A and B). We set up an Gaussian continuous-variable entanglement source in building A, consisting of two squeeze lasers to generate two-mode squeezed states. They are shared between the two buildings via a 1 km optical fiber. In both buildings, the entangled states are measured with self-designed and self-built balanced homodyne detectors. Due to the entanglement, the results are quantum random (truly random) but also correlated and can be used to generate a secret key. Attacks on the channel as well as on devices in building B reduce the entanglement strength and can thus be quantified. A major challenge in this setup is the phase stabilization and measurement synchronization between the two buildings. The fibers pick up extra noise, such as seismic and acoustic and experience temperature drifts. In this work, I will introduce the experiment, discuss the problem of phase noise and our approach to a control scheme. The first results with squeezed (not entangled) states show promising results for a phase lock of entangled states.