Preparation of non-classical photon states in laser-driven quantum-dot-cavity systems under the influence of acoustic phonons

在这个项目中，我们将探索在量子点腔系统中制备非经典光子态的理论可能性，例如Schrödinger-cat态，Fock态或偏振纠缠双对态。这种状态不仅可以用来测试量子力学的基础知识，还可以作为光子学、量子信息处理和量子密码学可能应用的核心构建块。我们将研究不同的激光激发能在多大程度上操纵量子点-腔系统中的光子态。特别令人感兴趣的是在基于半导体的量子点系统中无法避免的与晶格振荡（声子）相互作用所引起的新的物理效应。声子可能是制备的障碍；但声子辅助工艺也有可能实现新的制备方案。我们还将研究在谐振腔中由双激子（即具有两个电子-空穴对的状态）衰变产生的光子对在多大程度上可以受到外部激光场的影响，以及声子在这种情况下起什么作用。此外，到目前为止尚未探索的可能性之间切换不同类型的纠缠将被调查。两次相关函数的评估应避免通常调用的量子回归定理，该定理对具有非马尔可夫环境的系统无效（这里由声子提供）。二次相关函数与可测量量直接相关，包含光子非经典性质的重要信息。通过模拟光子系统的关键量，如不可分辨性、相干性、纠缠度以及记录n光子束的光子统计，有望发现新的物理见解，特别是对非马尔可夫效应的重要性。本项目中的所有计算都将使用数值完整的路径积分方法进行，而不会与通常使用的模型有任何近似。对于这里研究的量子耗散多层次系统，由于申请人小组在方法上取得的进展，这种完整的处理直到最近才成为可能。首先，研究表明，即使是先进的、建立良好的近似方法，在与实践相关的参数范围内，也会导致与数值完整结果的较大偏差。光子性质的误差特别大，这是本项目的重点。因此，数值完备的处理对于得出结论性的结果是决定性的。

In this project we shall explore theoretically possibilities to prepare non-classical photon states, such as, e.g., Schrödinger-cat states, Fock states or polarization entangled two-pair states, in quantum-dot-cavity systems. Such states can not only be used to test the basics of quantum mechanics but also serve as central building blocks for possible applications in photonics, quantum-information-processing and quantum-cryptography.We shall investigate in how far the photon state in a quantum-dot-cavity system can be manipulated by different laser excitations. Of particular interest are the new physical effects evoked by the interaction with lattice oscillations (phonons) which cannot be avoided in semiconductor based quantum dot systems. Phonons may be an obstacle for the preparation; but it is also possible that phonon-assisted processes may enable new preparation protocols.We shall also study how far the generation of photon-pairs, which arise from the decay of a biexciton (i.e. a state with two electron-hole pairs) in the resonator, can be influenced by external laser fields and what role phonons play in this case. Also the so far unexplored possibility to switch between different types of entanglement will be investigated.Two-time correlation functions shall be evaluated avoiding the usually invoked quantum regression theorem which is not valid for systems with a non-Markovian environment (here provided by the phonons). Two-time correlation functions are directly connected to measurable quantities and contain important information about the non-classical properties of photons. New physical insights in particular into the significance of non-Markovian effects are expected to be found by simulating key quantities of photonic systems such as the indistinguishability, the coherence, the degree of entanglement as well as by recording the photon statistics of N-photon bundles.All calculations within this project will be performed using numerically complete path-integral methods without any approximation to the usually used models. For the quantum-dissipative multi-level systems studied here, such a complete treatment has become available only recently due to a methodological progress reached by the group of the applicant. First studies reveal that even advanced well established approximate methods lead to large deviations from the numerically complete results in praxis-relevant parameter ranges. The errors are particularly large for photonic properties, which are the focus oft the present project. Thus, the numerically complete treatment is decisive for reaching conclusive results.