Experimental Study on Quantum Coherence in Solids

我们首次观察到法诺效应的明显迹象，这是量子点和量子环组合系统中相移和干涉的结果。这一观察导致了对量子相干性的新认识，例如，范诺参数的性质。我们也应用这一效应来研究量子相干性的各种问题。例如，我们清楚地观察到量子相的静电控制，并找到了一种新的理论方法来处理量子相的热展宽，并应用于分析实验结果。特别是，我们对长期存在的“同相库仑峰”问题给出了部分答案。我们进一步发现了量子点中强耦合态的存在，并且通过有序共振隧道和通过强耦合态的共隧道的多级输运导致没有任何外部参考臂的量子点中的Fano干涉。观察到外加磁场使强耦合态聚焦并平滑过渡到最外边缘态。利用量子环结构研究了量子点的自旋态与量子相干性之间的关系。我们发现自旋散射通过在局部自旋和穿越电子的自旋之间形成量子纠缠态而引起量子退相干。我们已经证明了通过在二维电子上的磁修饰对电子路径的相干控制。我们在量子反点系统的磁阻中发现了一种新的量子振荡。

We have observed, for the first time, clear sign of the Fano effect, which is a consequence of phase-shift and interference in a combined system of a quantum dot and a quantum ring. The observation leads to new knowledge of quantum coherence, e.g., the nature of Fano parameter. We have also applied this effect to investigate various problems on quantum coherence. For example, we have clearly observed electrostatic control of quantum phase and found a new theoretical method to treat thermal broadening of the quantum phase, which is applied to analyze experimental results. Especially, we have given a partial answer to a long standing problem of "in-phase Coulomb peaks". We further found the existence of strongly coupled states in quantum dots and multi-level transport through an ordinal resonant tunneling and co-tunneling through a strongly coupled state results in Fano interference in a quantum dot without any outer reference arm. External magnetic field causes focusing of strongly coupled states and smooth transition to outmost edge states is observed.We have investigated the relation between the spin states in quantum dots and the quantum coherence by a quantum ring structure. We have found that the spin scattering causes quantum decoherence through the formation of quantum entangled states between a local spin and a spin of traversing electron.We have shown that coherent control of electronic path through magnetic decoration on two-dimensional electrons. We have found a new quantum oscillation in magnetoresistance of quantum anti-dot systems.