Theoretical Studies On The Quantum Coherence Effects And Their Applications In Semiconductor Quantum Wells

In the past decades, lots of interesting optical phenomena based on quantum coher-ence have attracted considerable interests for the optical properties of the media can be greatly changed due to the quantum coherence and interference, for example, electromag-netically induced transparency (EIT), laser without inversion (LWI), coherent population trapping (CPT), enhanced high-order nonlinearities, low group-velocity, enhanced index of refraction without absorption and so on. Additionally, for the realization of more flex-ible and high speed information processing, quantum coherent effects are also used to manipulate and control the quantum state of a single atom or photon efficiently. The phenomena based on quantum coherence mentioned above are mostly predicted and ob-served first in the atomic media. However, for their potential applications, solid media seem more valuable and worth researching and pursuing. In this thesis, we study mainly the quantum coherence effects and their applications in semiconductor quantum wells. More specifically, we theoretically investigate ultraslow optical soliton, highly efficient four-wave mixing (FWM), optical gain-absorption behaviors, and realization of the po-larization qubit phase gate and the two-mode continuous-variable entanglement in semi-conductor quantum well systems. The main content is as follows:1. We demonstrate the formation of ultraslow bright and dark optical solitons with a four-level scheme in an asymmetric semiconductor double quantum well (DQW) structure based on interband transitions (IBTs) by using a low-intensity pulsed laser radiation. With appropriate conditions we show numerically that the optical soliton can travel with a ultraslow group velocity Vg/c～10-5.2. We present a cascade configuration for the realization of highly efficient FWM process in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). The corresponding explicit analytical expres-sions for the input probe and generated FWM pulsed fields are derived by use of the coupled Schrodinger-Maxwell approach and the FWM efficiency versus several variables is also discussed in detail. In the proposed TCQW scheme, the efficiency of the generated FWM mid-infrared (MIR) signal is significantly enhanced and the obtained maximum efficiency is greater than 50%.3. We investigate the phase-dependent gain and absorption behaviors of mid-to far-infrared lights under a cascade configuration in an asymmetric semiconductor TCQW structure based on ISBTs. In the proposed TCQW scheme, the gain-absorption spectra are strongly dependent on the relative phase of the applied laser fields, and the amplification of the probe and signal fields, i.e., the far-and mid-infrared waves, can be realized with realistic experimental parameters. The influences of the probe detuning and the two pump Rabi energies on the gain-absorption responses of two weak far-and mid-infrared light fields are also discussed in detail.Then, using the similar approach we demonstrate the amplification and absorption response of the probe and signal fields in an asymmetric coupled-double-quantum-well nanostructure with a double-A configuration. We also analyze respectively the influences of the pump Rabi energies, Fano-interference strength, the relative phase, and the probe single-photon detuning on the absorption spectra. The results show that the amplification of the two weak fields can be realized by adjusting these parameters.4. Adopting the equations of probability amplitudes of the electronic wave functions to analyze the nonlinear optical response of two four-subband CQW systems, we obtain the relative analytical expressions of the susceptibilities of two weak pulsed fields. Based on the giant cross-Kerr nonlinearity, two-qubit polarization phase gates are realized in both CQW schemes, in which the binary quantum information is encoded by using the polarization degrees of freedom of the probe and signal fields.5. We investigate the generation and evolution of entanglement between two cavity modes in asymmetric DQWs trapped in a doubly resonant cavity by means of Fano-type interference through a tunneling barrier, which is different from the previous studies on entanglement induced by strong external driven fields in atomic media. It shows that the strength of Fano interference can influence effectively the time interval and degree of the entanglement between two cavity modes and the enhanced entanglement can be generated in this DQW system.In summary, this thesis may be helpful to deepen understanding of the quantum coherence effects in semiconductor quantum wells and their applications in quantum optics and quantum information processing, to learn more about the formation of the ultraslow optical soliton, about the generation, absorption, and amplification of the in-frared fields, and about the realization of the polarization qubit phase gate and two-mode continuous-variable entanglement based on the quantum coherence. These studies may be with some reference value for the developments and applications of optical buffer, infrared laser, infrared light amplifier and quantum information processing technology.