The Department of Physics, Stockholm University
Ashraf Mohamed El Hassan
Monday 16 September
09:00 - 12:00
Quantum information science, the rapidly developing interdisciplinary field, gives power to the information and communications technologies (ICT) by providing secure communication, precision measurements, ultra-powerful simulation and ultimately computation. It is well known that the photons are ideal candidate for encoding the quantum bit, or ‘qubit’, in quantum information.This thesis consists of two main parts. In the first part, realization of quantum security tasks using optical fibers has been implemented. Bell tests are a cornerstone of quantum key distribution and are necessary for device-independent security. Device-independent Bell inequality test must be performed with care to avoid loopholes. Time-energy entanglement has the distinct advantage over polarization as it is easier transmitted over longer distances, therefore, it may be preferable as quantum resource to perform reliable key distribution. Novel multiparty communication protocols: secret sharing, detectable Byzantine agreement, clock synchronization, and reduction of communication complexity, all these quantum protocols has been realized without compromising on detection efficiency or generating extremely complex many-particle entangled states. These protocols are realized in an optical fiber setup with sequential phase modulation on single photons.In recent years there has been great interest in fabricating the ICT optical setups in low scale in glass chips, which would replace the bulk setups on tables used today. In the second part of the thesis, realization of photonics waveguides in glass has been implemented. Using femtosecond laser inscription of waveguides in glass, photonics quantum technologies and integrated optical circuits are becoming more and more important in miniaturization of optical circuits written in different glass samples for quantum optics and quantum information processing. These platforms offer stability over the time-scales required for multiphoton coincidence based measurements. The study and optimization the different building blocks for integrated photonics quantum circuits, for instance the Directional coupler and Mach-Zehnder interferometer is very important. The principal goal is to develop a method for design, fabrication and characterization of integrated optics circuits for further applications in quantum information. Incorporation of photon sources, detectors and circuits integrating waveguides technology can be used to produce integrated photonics devices.