Large cross phase modulation using double electromagnetically induced transparency.

摘要

This thesis deals with the engineering of accumulated cross-phase modulation (XPM) cross phase shifts (XPS) between two weak pulses based on large coherent nonlinear interaction enhanced by a medium that exhibits Electromagnetically Induced Transparency (EIT). Applications of such nonlinear phase shifts in optical quantum information processing (OQIP) are also investigated.;I show how to implement this promising scheme with the D1 line of 87Rb atomic gas by applying a static magnetic field with moderate intensity. This magnetic field perturbs the atom levels according to the nonlinear Zeeman effect and thus the perturbed atomic levels provide the atomic configuration needed for this scheme. A tripod configuration inherent to the D1 line is used to create DEIT for both signals and thus allows one to slow down both signals and to flexibly manipulate the group velocities of both. I numerically simulate the master equation for this 16-level system and find a good agreement with the simplified 5-level N-Tripod system.;I also investigate applications of such large XPM in OQIP. As shown in current Controlled-Phase gate (CPHASE gate) proposals based on XPS, the phase shift caused by XPM for pulses having matched group velocities would have a similar profile with the pulse shape of the single-photon pulse, which precludes a high-fidelity operation. I propose a high-fidelity CPHASE gate by adopting a strategy to generate large uniform XPS (UXPS) for both signals. This UXPS leaves the mode structure of the single photon pulses intact and thus greatly improves the fidelity of the proposed CPHASE gate operation. I develop a multi-mode quantum theory to derive the analytical results and identify the conditions of producing such UXPS. A simulation of the implementation UXPS with the proposed 5-level N-Tripod system is given by solving the one dimensional paraxial equations with classical input pulses containing single-photon energy. This method would also allow people to build high-fidelity optical switches for two light pulses and Quantum Nondemolition (QND) Measurement devices.;I present a novel theoretical model to generate large XPM coefficients between two pulses while simultaneously creating Double Electromagnetically Induced Transparency (DEIT) for both signals so that detrimental effects such as absorption and distortion are significantly suppressed, leading to a large accumulated XPM XPS with near-zero absorption. Analytical solutions are derived to demonstrate the dominant physical processes. These solutions are based on analytical methods that use perturbation theory under adiabatic conditions. I also produce accurate solutions by numerically simulating the master equation and the one dimensional paraxial equation.