Shamsolah Salemian

Ph.D. Thesis Defense Session

Abstract

Quantum communication system transmits quantum information from one point to another point. Distribution and control of entanglement in global scale is required in long-distance quantum communication. Now, the only suitable system for long-distance quantum communication is photon. Photon-based protocols suffer from photon loss and quantum decoherence in quantum channels. These problems limit range of single photon transmission up to several tens of kilometers in silica fibers. This problem can be solved by dividing the long distances into shorter intervals, so that the entanglement can be preserved in the shorter distances. System, which is responsible for this task, is called quantum repeater. In this thesis, quantum repeater design is done and its components are introduced. Relation between the components and performance of quantum repeater are described. Then design, simulation and implementation of some subsystem of the quantum repeater are done. Two distinct methods are presented for entangled photon pair source. First method is based on optical integrated circuits and other is based on the linear optic components. In the scheme based on optical integrated circuits, the grating waveguides are used and entangled photon pairs with wavelengths 692 nm and 950 nm are produced. Method Based on linear optics devices is experimentally done on the optical table in the Laboratory. Laser diode with 405 nm wavelength and BBO nonlinear crystal are used in experiment. Entangled photon pair is produced in wavelength of 810 nm. Total 88 pairs of entangled photon are measured at time interval of 30 sec. On the other hand, quantum gates such as NOT and CNOT are designed and simulated based on planar lightwave circuits. By using these gates, a scheme is presented for quantum state swapping. Polarization beam splitter is used as a key element in Bell states measurement. By using integrated optics method, an optical polarization filter is designed that its function is equivalent to the polarization beam splitter. Distribution of quantum entanglement is the main infrastructure of quantum communication and quantum repeater. New protocol will presented for the distribution of entanglement. This protocol can detect and correct qubit error in the quantum channel.

Date: Wednesday 29 Dec. 2010 Time: 13:00

 Place: Room 305, School of Electrical Engineering