N-qubit entanglement of encoded qubits via curvature couplings to a superconducting cavity and joint continuous measurement

We propose entangling preparation procedures based on curvature couplings of encoded qubits to a superconducting (SC) cavity, exploring the non-linear qubit response. The proposed scheme allows
a joint continuous measurement on selected qubits via the SC cavity, generating N-qubit entanglement (at times of 10s of ns), as well as N-qubit backaction phases (in the homodyne scheme). These results are applied to encoded qubits (including spin-qubits or superconducting qubits) residing in their ``full sweet spot'' to gate fluctuations, where qubits' dipole moment is zero and qubit dephasings are minimized, see e.g., Refs.[1,2]. The more standard case of (dispersive) dipole coupling to the resonator is also considered. The influence of the backaction phases as well as of various qubits' gate noises on the entangling fidelities are considered. The proposed scheme seems suitable for remote entanglement-by-measurement preparation of various encoded qubits.

[1] Rusko Ruskov, Charles Tahan, Phys. Rev. B99, 245306 (2019) and arXiv:1704.05876
[2] Rusko Ruskov, Charles Tahan, arXiv:2010.01233