Speaker
Description
We propose a generalized fluxonium circuit hosting $d$ low-lying energy levels, well separated from the rest of the spectrum and that naturally realize a qudit system protected from leakage errors. The low-energy states are constituted by fractional fluxon states, localized in the minima of a suitably designed Josephson potential and weakly hybridized by quantum phase slip processes. The potential is tailored through a Fourier engineering approach, that employs multi-harmonics Josephson elements, which are in turn obtained from basic conventional elements by a proper scheme. We present the spectrum of a $d=4$ and a $d=5$ qudit system and then focus on the most relevant qutrit case. We analyze the dipole matrix elements for coupling to the radiation and we propose a non-Abelian, stimulate Raman adiabatic passage (STIRAP) protocol for single-qutrit gates, that is particularly suited for the present system. The proposed platforms opens novel perspectives in circuit engineering and quantum computing beyond the qubit paradigm.