Two-Qubit Gates with Fluxonium Circuits.*

Among superconducting qubits, the fluxonium offers a unique advantage of the possibility to use different transitions for memory storage and gate realizations [1]. In this talk, we discuss various ways to make entangling gates between fluxoniums using noncomputational levels of the two-qubit system. In one example, a controlled-Z gate is activated by driving a transition leading out of the computational subspace while two qubits are kept at fixed frequencies at their sweet spots [2]. The second example is based on adiabatic tuning of one or both of the qubits away from their sweet spots towards the avoided level crossing between a computational and noncompuational levels [3]. One more possible gate is mediated through a common resonator mode. We compare all the techniques and discuss their advantages and limitations.

[1] L. B. Nguyen, et. al., arXiv:1810.11006 (2018).
[2] K. N. Nesterov, et. al., Phys. Rev. A 98, 030301 (2018).
[3] L. DiCarlo, et. al., Nature (London) 460, 240 (2009).