Strong longitudinal (curvature) couplings for encoded spin qubits near charge degeneracy

Typically, encoded spin qubits such as DQD S-T qubit, TQD AEON qubit, etc. exhibit strong transverse (dipole) coupling at or near charge degeneracy, which is used to couple to a superconducting resonator in the dispersive regime to perform quantum measurements or gates. Here we theoretically show, see Refs. [1,2], that at or near charge degeneracy there might appear a comparable or even stronger longitudinal (energy curvature) couplings with implications for improved quantum measurements. Non-adiabatic corrections to this picture are also discussed.

 

[1] R. Ruskov and C. Tahan, Phys. Rev. B 103, 035301 (2021).

[2] R. Ruskov, C. Tahan, M. A. Eriksson group (UW-Madison), R. McDermott (UW-Madison),

W. D. Oliver group (MIT Lincoln Lab), in preparation.