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

• Applicant: Dr. Alexander Stibor
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 265596161

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.

• DFG Programme: Research Grants