光與物質交互作用研究-化合物半導體共振腔量子電動力學

Abstract

本計劃為一新提三年計劃，我們將探討光與物質之交互作用，特別是具半導體垂直共振腔結構中之量子電動力學(Cavity Quantum Electrodynamics CQED)。因化合物半導體長晶技術之快速提升，具DBR反射鏡垂直共振腔結構之CQED已成為最重要之研究系統。若半導體垂直共振腔中g為光場與物質之耦合強度、κ為Cavity內光子之衰減速率 、而γ為非共振光子之衰減速率，當 g＞＞κ，γ時，CQED屬於強耦合之範疇，此狀態下光與物質之交互作用是遠快於非可逆性過程中之光損耗，此時光吸收與放射成為一可逆性之過程，光會在非共振損耗前被物質再吸收而放射。微共振腔內極化激子即是半導體量子井內之激子與光子在強強耦合交互作用下，所形成之一種半物質/ 半所光結合成之準粒子。我們將特別投入此種與面射型垂直共振腔雷射(VCSEL)相同結構之系統，研究強耦合下超流體及微共振腔極化激子雷射形成之機制。因VCSEL Lasing屬於CQED中之弱耦合(weak coupling)，為達到強耦合之範疇，我們將重新設計稱成長磊晶結構，重點將在提高g值與降低κ，γ。改變之重點將是提高DBR反射鏡之反射率，並藉降低氧化層之位置以降低側向光子之損耗。預期從全新設計製作之半導體垂直共振腔結構將可產生強耦合交互作用下。我們會特別注意大角度圓環狀之輻射及其近場coherent 特性，並觀察其是否有臨界點及特定之光偏振態出現。這些特性都與超流體波函數直接相關，故可以其作為超流體出現之重要檢驗依據。我們也會注意VCSEL雷射臨界電流以下之螢光光譜，初步實驗顯示共振腔極化激子雷射已有出現之跡象。以我們過去在VCSEL 及相關coherent patterns 多年之經驗，相信必然可在microcavity polariton超流體方面獲得不錯之成果。

In this three-year proposal, we will study the interaction between light and matter, particularly the cavity quantum electrodynamics (CQED) in semiconductor vertical cavity structure. Due to recent advancement in compound semiconductor growth technology, optical cavities of vertical structure composed of distributed Bragg reflectors (DBRs) have become the most important systems for the study of cavity quantum electrodynamics. Assuming that g ,κ，andγare the coupling strength of optical field and dipole, photon decay rate in the cavity, and non-resonant decay rate respectively, if g＞＞κ,γ, CQED is said to be in the strong coupling regime, in which light and matter interaction is under a reversible process and light can be reabsorbed and efficiently reemit before it is lost in non-resonant decay. The semiconductor vertical microcavity polariton is the result of this strong interaction, a quasi-particle with the character of half matter and half light. We will investigate the formation mechanism of microcavity polaritons and superfluidity in these optical systems, which are known to be similar to the vertical cavity surface emitting lasers (VCSEL), and which we have studied for more than ten years. VCSEL lasing is said to be in the weak coupling regime and in order to achieve strong coupling, we propose to raise g and decreaseκ，γby redesigning the Q value in the cavity and lower the oxide layer to increase optical lateral confinement. It is expected that the recent reported polariton lasing and superfluidity phenomena will be observed in our new systems. Based on previous experiences in the study of the coherent emission patterns from broad area VCSELs, we have confidence that high quality results can be generated from this project.