Direct dipole coupling between a two-level system and a bosonic mode describes the interactions present in a wide range of physical platforms. In this work, we study a coupling that is mixed between two pairs of quadratures of a bosonic mode and a spin. In this setting, we can suppress the dispersive shift while retaining a nonzero Kerr shift, which remarkably results in a cubic relationship between shot noise dephasing and thermal photons in the oscillator. We demonstrate this configuration with a simple toy model, quantify the expected improvements to photon shot-noise dephasing of the spin, and describe an approach to fast qubit readout via the Kerr shift. Further, we show how such a regime is achievable in superconducting circuits because magnetic and electric couplings can be of comparable strength, using two examples: the Cooper pair transistor and the fluxonium molecule.
@article{arxiv.2503.13411,
title = {Mixed spin-boson coupling for qubit readout with suppressed residual shot-noise dephasing},
author = {Jinlun Hu and Antonio L. R. Manesco and André Melo and Taryn V. Stefanski and Christian Kraglund Andersen and Valla Fatemi},
journal= {arXiv preprint arXiv:2503.13411},
year = {2025}
}