Decoherence of an electronic and macroscopic superposition state by interaction with a superconductor

从量子力学到经典系统的分析是现代物理学基础的一部分。这种量子性质的损失可以用退相干理论来描述。它具有基础性和技术相关性，例如，对于混合量子系统的实施。在这个项目中，将实现一个模型系统，其中双棱镜干涉仪中的宏观和电子叠加态通过库仑相互作用耦合到超导环境。因此，电子波被一根带电的细线分离并相干地组合在一起。在部分波重叠和干涉之前，它们在几十微米的可变距离内穿过超导表面。这导致了超导体中电子物质波和库珀对之间的库仑相互作用。它对叠加态的消相干有直接影响，叠加态可以通过干涉图案中的对比度损失来测量。在计划中的项目中，由于施加了超导体，表面的电阻完全消失了，这与以前用半导体表面附近的电子进行的退相干实验相反。研究表明，对于半导体来说，由于电子路径下方形成的镜像电荷，这一电阻准确地导致了信息到达环境的路径，从而导致了退相干。由于材料中的电阻，各种理论模型假定像电荷的摩擦力为耗散项。因此，随着电子路径之间距离的增加和到表面距离的减小，对比度逐渐丧失。然而，超导体上方的电子叠加态的性质不能用以前的理论来描述。它将在这个项目中进行详细的实验研究。此外，由于这种电子叠加态在金属和可变掺杂的半导体表面上的退相干，还将涉及一些悬而未决的问题。以前的预测只能描述在特定半导体上测量的消相干分布，而不能提供消相干强度的描述。它将用目前的方法在表面上测量，电阻率可以变化高达9个数量级。理论上认为，退相干还取决于表面的温度。因此，当表面温度在4-500K之间时，将测量叠加电子态的消相干，然后将结果与当前的消相干模型进行比较。这样做的目的是对导体和超导表面附近的消相干机制进行正确的描述。

The analysis of the transition from a quantum mechanical to a classical system is part of the foundations of modern physics. This loss of quantum properties is described by the theory of decoherence. It is of fundamental and technical relevance, e.g. for the implementation of hybride quantum systems. In this project a model system will be realized, where a macroscopic and electronic superposition state in a biprism interferometer couples to a superconducting environment by Coulomb interaction. Thereby an electron wave gets separated and combined coherently by a thin electrostatically charged wire. Before the partial waves overlap and interfere, they traverse a superconducting surface in a variable distance of a few ten micrometers. This results in a Coulomb interaction between the electronic matter wave and the Cooper pairs in the superconductor. It has a direct influence to decoherence of the superposition state that can be measured by a contrast loss in the interference pattern. In the planned project the electric resistance disappears completely in the surface because of the applied superconductor, in contrary to former decoherence experiments with electrons nearby semiconducting surfaces. It was shown for semiconductors that due to the formation of image charges below the electron paths, exactly this resistance leads to a which-path-information to the environment and consequently to decoherence. Various theoretical models assume a dissipative term for the friction of the image charge, as a consequence of the electric resistance in the material. A gradual loss of contrast is therefore observed with increasing distance between the electron pathways and with decreasing distance to the surface. However, the properties of the electronic superposition state above the superconductor cannot be described with previous theories. It will be studied experimentally in detail within this project.Furthermore open questions will be concerned according decoherence of such an electronic superposition state above metallic and variable doped semiconducting surfaces. Previous predictions could only provide a description of the measured decoherence distribution above a certain semiconductor but not for the strength of decoherence. It will be measured in the current approach above surfaces with electric resistivities that can be varied by up to nine orders of magnitude. It is theoretically assumed, that decoherence depends also on the temperature of the surface. Therefore decoherence of the superposed electronic state will be measured with surface temperatures between 4 and 500 K. The results will then be compared to current decoherence models. The aim is to develop thereby a correct description of the decoherence mechanisms near conducting and superconducting surfaces.