M.Sc Thesis

M.Sc StudentHayat Alex
SubjectIntegrated Photonic Devices for Quantum Communications
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Meir Orenstein
Full Thesis textFull thesis text - English Version


            In this research we study different realizations of practical integrated quantum-optical devices for quantum communications by harnessing fundamental physical laws to improve the acquisition, transmission, and processing of quantum information.

            Many of the practical devices for quantum communications are based on processing photons by nonlinear optics. Semiconductors are promising materials due to their high nonlinear susceptibilities and compatibility with the existing photonics technology. Furthermore, semiconductor quantum structures can be designed to meet particular requirements of specific optical response and frequency range, and enhance the nonlinear properties of the material.

            We demonstrate the design of semiconductor quantum well (QW) structures that modify the material dispersion locally according to the frequency requirements of the optical parametric nonlinear process while strongly enhancing the nonlinearity. We demonstrate a cavity self-phasmatching concept for materials which cannot be phase-matched by conventional means. High quality factor cavities are also shown to serve as storage for the produced photons and generate time-separation between exiting photons for photon-number-resolved detection. We designed and fabricated integrated semiconductor (GaInP/AlGaInP) microcavities for self-phasematched second harmonic generation, employing a newly developed technique for high-aspect-ratio focused ion beam semiconductor nano-patterning.

            The efficiency of any devices based on all-optical c(2) nonlinear process is limited due to the weak fundamental interaction described by a third-order nonlinear process in the time-dependent perturbation theory combined with a first-order process of the pump laser emission. Moreover, all-optical nonlinear interaction requires dispersion compensation techniques. Semiconductors, however, allow manipulation of free charge carriers, and thus more efficient low-order nonlinear processes can be used involving generation and recombination of charge carriers. We propose efficient processes of two-photon absorption and two-photon emission in semiconductors as foundations for novel building blocks for quantum communications.

            We analyze high-efficiency room-temperature entangled-photon pair generation based on two-photon spontaneous emission from QWs in a photonic microcavity. We also demonstrate what appears as the first experimental observation of spontaneous two-photon emission from semiconductors. The overall two-photon emission is relatively strong due to the continuous energy band structure of semiconductors. The measured wide-band two-photon emission spectrum is blue-shifted in contrast to the two-photon emission from discrete-level atomic systems.