Manuscript of the thesis
Abstract:
Mesoscopic quantum physics studies solid-state systems smaller than the electronic coherence length, where the wave nature of electrons plays a central role in electronic transport. Our group conducts experiments in Electronic Quantum Optics (EQO) to exploit this quantum behavior, particularly to create flying electronic qubits for quantum computing.
This thesis focuses on the realization of an electronic Mach-Zehnder interferometer (MZI) in graphene, a two-dimensional material. In the quantum Hall effect regime, the bulk of 2D systems becomes insulating, and current flows through ballistic, chiral 1D edge channels, which act as optical fibers for electrons. In a gate-defined PN junction in graphene, the edge channels co-propagate along the junction, and electrons can tunnel from one channel to the other at the physical edge of the sample, thereby defining electronic equivalents of separating slits; two such slits in series form an MZI. This device was characterized under DC conditions, demonstrating tunable separation slits and electronic interference, with a visibility greater than that of interferometers previously implemented in other 2D systems (GaAs).
I have explored several developments of this system with the goal of implementing flying qubits, in particular on-demand injection and the characterization of single electrons, analogous to single-photon sources. Periodic GHz voltage pulses, calibrated to carry one electron charge per pulse, are injected into the device. Floquet scattering theory predicts that most pulse shapes generate excess particles, which are sources of decoherence. Lorentzian pulses, on the other hand, produce so-called “Levitons”—purely electronic excitations without additional particles—which thus constitute our source.
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