全雷射冷卻量子氣體之儀器架設與最佳化

Abstract

稀薄量子氣體，尤其是玻色-愛因斯坦凝聚態 (BECs)，一直是多體物理學研究與量子感測技術不可或缺的實驗基礎。不過，此領域的發展長期受到常規「蒸發冷卻」技術的限制。這種耗時達數秒的冷卻機制效率不彰，往往會流失超過90%的初始原子，嚴重限縮了最終生成的冷原子總數。為了解決這項技術瓶頸，我們團隊轉而發展全光學的雷射冷卻路徑，期望在大量減少製備週期的同時，盡可能留存最多的原子。 在此高速且全光學的運作架構中，電磁誘發透明 (EIT) 冷卻技術扮演了最核心的角色。過去，我們實驗室曾借助該機制順利生成銣-85 (85Rb) 量子氣體；但因85Rb 原子間具有等效的吸引力交互作用，導致其凝聚態在達到高密度時容易失去穩定性。為此，我們將目標轉向具有等效排斥力、狀態更為穩固的銣-87 (87Rb) BEC。本篇論文完整論述了針對該目標所建置的全光學冷卻硬體平台，並詳細說明了架設期間進行的各項系統調校。 藉由精調實驗設備，包含涵蓋 EIT 雷射參數及光束空間配置，並導入準確的溫度測量方法，我們期望能進一步突破冷卻極限，同時獲取最大的捕獲原子量。這些紮實的儀器開發與優化工作，將為未來打造高產能、具擴充潛力的量子元件，可應用於精密計量與量子資訊科學等領域提供穩固的基石。

Dilute quantum gases, particularly Bose-Einstein condensates (BECs), have become a widely used platform for exploring many-body physics and implementing quantum sensors. However, many conventional preparation sequences rely on evaporative cooling, which can be slow and atom-loss intensive. This slow, multi-second process heavily restricts the cooling time and is profoundly inefficient, typically sacrificing over 90% of the initially trapped atoms, thus limiting the final cold atom number. To overcome this bottleneck, we aim to utilize an all-laser cooling approach to significantly shorten the preparation time while maximizing the retained atom number. A key technique in this rapid, all-optical sequence is Electromagnetically Induced Transparency (EIT) cooling. Our research team has previously applied this technique to successfully produce a quantum gas of 85Rb; however, the effectively attractive atomic interactions of 85Rb rendered the resulting condensate unstable at high densities. Driven by the ambition to realize a stable 87Rb BEC featuring effectively repulsive interactions, this thesis details the apparatus construction for the entire all-laser cooling system. Furthermore, it presents the optimization of the system throughout the setup process. By optimizing the experimental apparatus, including the EIT laser parameters and beam configurations, and implementing robust thermometry, we aim to maximize the trapped atom number and achieve lower cooling temperatures. This rigorous apparatus development lays the essential groundwork for realizing high-flux, scalable quantum devices for high-precision metrology and quantum information science.