Quantum random number generation and quantum scissors for secure communications

This thesis presents the results of two experiments realized for my PhD project. Both are explained in the context of quantum communications, with a long term goal of establishing a secure method of message exchange.
One requirement for the development of a quantum communication system is the possibility of generating random numbers. Based on the Entropy Accumulation Theorem [1], we are able to certify more randomness than conventional methods [2]. We constructed a semi-device independent optical setup to performed an experiment to be was analysed under this new method [3]. We obtained more than 1 bit of randomness per round of the experiment, without assuming that the rounds of our experiment are independent and identically distributed (i.i.d.), loosening the common requirements for this type of experiment. Our final result was an extraction of 1.319(2) random bits per round.
The other experiment realized for the work of this thesis dealt with an actual communication protocol, based on the architecture of a quantum scissor [4]. This optical device was first proposed as a means for quantum state engineering of two-level systems, but it shows promising characteristics useful for quantum communications [5]. For instance, with such a system it is possible to teleport weak coherent states with good fidelity [6]. More interestingly, it can be used as a QKD device and it allows us to obtain a secret key rate which is better than the one imposed by the PLOB bound, even without using quantum memories [7]. We were able to fully build the setup on the optical table and we took some preliminary teleportation data, which serves as a preparation for a future QKD implementation of the device.