Towards a pointing system for free-space quantum key distribution

Abstract

In chapter 1: We start with introducing the field of quantum key distribution, the development done in it till the current date, the possible physical methods to to implement it in free space and to implement using the optical fibers and their comparison with respect to the physical implementation and efficiency. After that I introduce the problem statement for my thesis which is the balloon to ground quantum communication. In chapter 2: We discuss the field of cryptography and the One time Pad system which is used in day to day life. Then we discuss what information actually is, how can we quantify it, and the current classical algorithms used. Then we introduce the quantum mechanics and it’s fundamental properties. Then we delve into the main topics for the development of the quantum key distribution viz. Entanglement and No-cloning theorem. Then we go to the topic of Quantum Key distribution and explore the prominent protocols in use. In chapter 3: In this chapter we discuss the actual experimental methods which are imple- mented during my work. We start with discussing the spontaneous parametric down conversion process where two photons are generated from a single pump photon. We discuss the apparatus required for it viz. the non-linear crystal and it’s specification. Then we go into the optical beam experiment were we create an entangled photons beam starting from creating a gaussian beam profile to placing the crystal in right position to going in the experiment to tune the temperature of the crystal to enhance the entanglement and finally we measure the S-parameter to certify that we have created entangles photons. Then we go into the technological domain of the project where we focus on the concept of mode-matching which is required for receiving the optical signal. We discuss the embedded systems and feedback loops required for this process. Finally we see the optical setup where the beacon laser beam is used to guide the required quantum beam to mode-match with the collimator.