[论文解读] Using the Autler-Townes and ac Stark effects to optically tune the frequency of indistinguishable single-photons from an on-demand source

Chris Gustin, Łukasz Dusanowski+2 more|arXiv (Cornell University)|Jan 9, 2022

Quantum Information and Cryptography参考文献 91被引用 6

一句话总结

该论文提出了一种全光学方法，通过利用半导体量子点中的自旋-轨道耦合效应，结合光学腔体增强发射效率和光子不可区分性，实现对按需产生单光子频率的调控。该方法采用共振驱动（Autler-Townes效应）或非共振驱动（ac Stark位移）来实现频率调谐。在真实条件下，能量位移高达数百µeV时，光子不可区分性超过90%；当能量位移在数十µeV以内时，不可区分性接近100%。

ABSTRACT

We describe how a coherent optical drive that is near-resonant with the upper rungs of a three-level ladder system, in conjunction with a short pulse excitation, can be used to provide a frequency-tunable source of on-demand single photons. Using an intuitive master equation model, we identify two distinct regimes of device operation: (i) for a resonant drive, the source operates using the Autler-Townes effect, and (ii) for an off-resonant drive, the source exploits the ac Stark effect. The former regime allows for a large frequency tuning range but coherence suffers from timing jitter effects, while the latter allows for high indistinguishability and efficiency, but with a restricted tuning bandwidth due to high required drive strengths and detunings. We show how both these negative effects can be mitigated by using an optical cavity to increase the collection rate of the desired photons. We apply our general theory to semiconductor quantum dots, which have proven to be excellent single-photon sources, and find that scattering of acoustic phonons leads to excitation-induced dephasing and increased population of the higher energy level which limits the bandwidth of frequency tuning achievable while retaining high indistinguishability. Despite this, for realistic cavity and quantum dot parameters, indistinguishabilities of over $90\%$ are achievable for energy shifts of up to hundreds of $\mu$eV, and near-unity indistinguishabilities for energy shifts up to tens of $\mu$eV. Additionally, we clarify the often-overlooked differences between an idealized Hong-Ou-Mandel two-photon interference experiment and its usual implementation with an unbalanced Mach-Zehnder interferometer, pointing out the subtle differences in the single-photon visibility associated with these different setups.

研究动机与目标

• 开发一种基于全光学控制的可调谐、按需产生单光子源，具备高不可区分性和高效率。
• 研究基于量子点的单光子源中频率调谐范围与相干性之间的权衡关系。
• 通过集成光学腔体，减轻自发辐射和电子-声子散射带来的性能退化。
• 阐明理想化Hong-Ou-Mandel干涉实验与实际非平衡Mach-Zehnder干涉仪实现之间的差异。

提出的方法

• 基于量子点双激发-单激发级联结构构建四能级阶梯系统。
• 在上能级跃迁附近施加与之共振的相干连续激光驱动，以诱导Autler-Townes效应或ac Stark效应。
• 采用主方程模型模拟动力学过程，量化光子不可区分性和发射效率。
• 将光学腔与激子跃迁共振，以提高光子收集速率并抑制退相干。
• 分析电子-声子散射和激发诱导退相位对光源性能的影响。
• 将理论预测与先前关于量子点单光子源的实验基准进行对比。

实验结果

研究问题

• RQ1 选择共振驱动（Autler-Townes）与非共振驱动（ac Stark）连续激光驱动，对频率调谐范围和光子不可区分性有何影响？
• RQ2 光学腔在该系统中如何减轻退相干并提升发射效率？
• RQ3 电子-声子相互作用在多大程度上限制了频率调谐范围，同时保持高不可区分性？
• RQ4 理想化HOM实验与实际非平衡Mach-Zehnder干涉仪中的可见度和干涉对比度有何差异？
• RQ5 在考虑真实量子点和腔体参数时，频率调谐范围、不可区分性和效率之间可实现何种权衡？

主要发现

• 通过光学腔增强发射，能量位移高达数百µeV时，光子不可区分性可超过90%。
• 即使在真实材料和腔体参数条件下，能量位移在数十µeV以内时，仍可实现接近100%的不可区分性（>99%）。
• ac Stark区域可实现更高的不可区分性和效率，但需要强驱动和大失谐，从而限制了调谐带宽。
• Autler-Townes区域可实现更宽的调谐范围，但受时间抖动影响，相干性下降。
• 电子-声子散射导致激发诱导退相位和双激发子布居增加，限制了高不可区分性下的调谐范围。
• 光学腔增强显著降低了自发辐射和退相位的影响，从而同时提升了效率和不可区分性。