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Interference of electrons and anyons in the quantum Hall (QH) regime has always been of fundamental
interest. Such measurements allow for studying the quantum statistics of quasiparticles. While a recent
observation of fractional interference in a Fabry-Perot interferometer (FPI) was reported, fractional
interference in a Mach-Zehnder interferometer (MZI) was never observed. The MZI is a true ‘two-path’
interferometer and is free of Coulomb interactions, thus responding solely to an Aharonov-Bohm (AB)
phase.
In this talk, I will discuss an observation of AB interference of the outer-most edge mode v=1/3 in bulk filling
v=2/5 in an MZI [1] with 2μm path length at ~10mK. While the maximum visibility of an interfering integer
mode (outer-most mode at v=2) was ~91%, the corresponding visibility in the fractional regime was ~20%.
With a pretty transparent QPCs of the v=1/3 mode (t>0.5), the partitioned, interfering, charge was found to
be e
*=e/3. As theoretically expected, a counter-intuitive flux periodicity was 0 – the flux quantum. This
integer-like periodicity directly results from AB + braiding interference [2]. The MZI is topologically different
from the FPI since one of its drains is enclosed inside the interfering loop – leading to this rather astonishing
behavior. Moreover, the visibility of the interference oscillation was found (and understood) to be
dramatically different than in FPI (or in the integer regime), peaking away from half transmission (in the
integer case) of the MZI. This built-in braiding of the MZI offers new capabilities in testing exotic QH states.
1. Kundu, H.K., et al., Anyonic interference and braiding phase in a Mach-Zehnder interferometer.
Nature Physics, 2023. 19, p. 515–521.
2. Law, K.T., D.E. Feldman, and Y. Gefen, Electronic Mach-Zehnder interferometer as a tool to probe
fractional statistics. Physical Review B, 2006. 74(4): p. 045319. |