Evidence for quantum Brownian motion in electron-wall systems*

In 1997 Anglin, Paz, and Zurek proposed a test for Caldeira and Leggett’s quantum dissipation theory, which provides a general framework that connects decoherence of a quantum particle to the Brownian motion caused by dissipative interaction with a background of quantum oscillators [1]. In their proposal, a free electron moving above a metallic surface is dragged by the induced image charge [2]. Coherence among position states of the electron is lost rapidly with time as the image charge locally perturbs the wavepacket in a stochastic manner. In 2007, Sonnentag and Hasselbach reported the first experimental realization of the proposal using an electron interferometer [3]. However, there was a large discrepancy between the theory and the measured decoherence rate. While the reason behind the discrepancy was not discussed in detail, it is possible that the semiconductor surface used in the experiment was not conductive enough for the theory to be valid. Recent decoherence experiments employed metallic surfaces in order to comply with the theory, but no decoherence was observed [4, 5]. In this talk, we report the first observation of electron-metal decoherence. We attain strong interaction between the electron wave and the metallic surface by sending a diffracted electron beam through a 1.5 mm long gold-coated microchannel, with a gap size of 1.7 µm. We find quantitative agreement between the observed peak broadening, visibility lost and the decoherence model. Our work demonstrates the feasibility of testing the Caldeira-Leggett theory using electron-wall systems.

[1] A. O. Caldeira and A. J. Leggett, Path integral approach to quantum Brownian motion, Physica A 121, 587 (1983).

[2] J. R. Anglin, J. P. Paz, and W. H. Zurek, Deconstructing decoherence, Phys. Rev. A 55, 4041 (1997).

[3] P. Sonnentag and F. Hasselbach, Measurement of decoherence of electron waves and visualization of the quantum-classical transition, Phys. Rev. Lett. 98, 200402 (2007).

[4] P. Beierle, L. Zhang, and H. Batelaan, Experimental test of decoherence theory using electron matter waves, New J. Phys. 20, 113030 (2018).

[5] N. Kerker, R. Röpke, L. M. Steinert, A. Pooch, and A. Stibor, Quantum decoherence by Coulomb interaction, New J. Phys. 22, 063039 (2020).