Implementation of CNOT and CPHASE gates between Fluxonium and Transmon Qubits

The goal of this research is to implement microwave-activated gates (CNOT and CPHASE) between a Fluxonium qubit and a Transmon qubit using a planar device architecture. This design features a fixed-frequency transmon capacitively coupled to a Fluxonium qubit, minimizing flux noise through reduced wiring. To reduce the crosstalk between the Fluxonium drive and the Transmon we use a selective darkening method [1]. We drive the Fluxonium at the Transmon's ∣0〉−∣1〉 frequency for Cross Resonance (CR) operations. This architecture of superconducting qubits promises advantage over the two Transmon CR schemes [2] due to Fluxonium's larger anharmonicity solving the frequency collision issue. It also promises faster gate speed compared to two fluxonium CR schemes [3] due to the larger matrix element of the Target qubit (Transmon). To address static ZZ interactions, we employ a two port differential AC Stark shift method [4] to cancel this coupling. This induced ZZ can also be tuned to further implement a CPHASE gate.

1.Nesterov, K. N., et al., Phys. Rev. Appl., 18(3), 034063 (2022).

2.Rigetti, C., & Devoret, M. PhysRevB.81.134507 (2010)

3.Dogan, E., et al. Phys. Rev. Appl., 20(2), 024011 (2023).

4.Xiong, H., et al., Phys. Rev. Res., 4(2), 023040 (2022).