Fluxonium Molecule, Theoretical and Experimental Results

A huge advantage of superconducting circuits as a platform for quantum computing is the wide variety of possible circuits in which one can encode quantum information, but a majority of the effort in the field is focused on single-node circuits. One relatively-simple multi-node circuit is the fluxonium molecule, consisting of two fluxoniums with a shared superinductor. Even with the restriction of operating the circuit at working points which are first-order-insensitive to flux noise in the two loops, there are many options for a logical encoding, each with their own dominant dephasing mechanisms and possible control schemes. We present a theoretical analysis of working points, their respective logical encodings, and potential as a protected qubit, as well as our experimental results demonstrating coherent control.