Léonid Glazman

Yale University
Quantum Dynamics of a Fluxonium Device

Recent development of a new type of a qubit, fluxonium, facilitated the observation of two elusive quantum effects. The first of the two is the produced by quasiparticles dissipative component of the Josephson current. The second one is the interference between separated in space quantum phase slips. The dissipative effect of quasiparticles was quantified by measuring the T1 time of the qubit. This latter measurement actually resolved the so-called "cosine-phi" problem which existed since the time the Josephson effect has been predicted. The interference of phase slips manifested itself via inhomogeneous broadening of the qubit oscillations frequency. Related microwave techniques, in conjunction with our theory, were also used to detect a few quasiparticles populating Andreev levels in superconducting nanobridges. This talk covers the theory of the fluxonium qubit, and its use in designing the experiments and interpreting the data. Furthermore, an extension of the theory examines ways to use microwaves for detecting Majorana states in superconducting quantum wires with strong spin-orbit interaction.

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