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Flip-chip fabry-perot electron interferometer

by Samuel Gaucher

Institution: McGill University
Year: 2016
Keywords: Physics
Posted: 02/05/2017
Record ID: 2134882
Full text PDF: http://digitool.library.mcgill.ca/thesisfile139078.pdf


Abstract

The fractional quantum Hall effect (FQHE) is well understood in within the composite fermions picture : in 2+1 dimensions, a change in the topology of electron configuration space leads to the emergence of anyons, quasiparticles with fractional exchange statistics ranging between Bose-Einstein and Fermi-Dirac. These composite fermions, made of electrons bound to magnetic flux quanta in a ratio expressed by the filling factor, act as charge carriers in two-dimensional electron gases (2DEG) and give rise to exotic Hall magnetoresistance quantization. However, the elusive filling factor 5/2 state of the FQHE seems to contain additional structure from which an even more peculiar behaviour could arise. The excitations of this state are speculated to display non-abelian braiding statistics, an aspect which raised significant interest due to possible Majorana-like quantum computing applications.In order to probe the statistics of the 5/2 state and verify if it has a non-abelian nature, it has been suggested to conduct interferometry experiments in which quasiparticles are undergoing braiding operations. Such experiments have been used in other states of the FQHE, confirming the existence of anyons and fractional statistics. Despite sustained effort, it has not yet been possible to achieve convincing interference measurements in the 5/2. The difficulty of this task is explained by the extreme fragility of the state, which appears only in pure ultra-high mobility 2DEG samples. It is believed, in addition, that the nanofabrication of interferometers on these substrates can induce impurities, notably through e-beam lithography, making it difficult to observe strong 5/2 features. To tackle the fragility of the 5/2 state, this research proposed to implement a flip-chip Fabry-Perot interferometer. The idea behind the flip-chip method is to fabricate the interferometers on separate substrates and to flip them on the 2DEG samples, as if they had originally been patterned on them. This approach leaves the 2DEG in pristine condition, hopefully increasing the chances of conducting convincing interferometry experiments. At this point, it has been possible to demonstrate that the flip-chip method works for low-dimensional transport experiments. Quantum point contacts (QPCs) mounted in flip-chip configuration could reproduce the characteristic 2DEG conductance pinch-off and quantization. Interferometers could be unmounted and retested on different 2DEGs, maximizing the nanofabrication yield. Signs of what could possibly be quantum interference of electrons have also been observed, although not on 2DEGs of high enough mobility to study the 5/2 state. L'effet Hall quantique fractionnaire (EHQF) est aujourd'hui bien compris dans le cadre du modèle des fermions composites: en 2+1 dimensions, la topologie de l'espace de configuration des électrons change et entraine l'émergence de ce que l'on nomme des anyons, des quasiparticules dont l'interversion est décrite par des statistiques fractionnaires à mi-chemin entre les statistiques de… Advisors/Committee Members: Guillaume Gervais (Internal/Supervisor).

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