36 research outputs found
Connecting nth order generalised quantum Rabi models: Emergence of nonlinear spin-boson coupling via spin rotations
We establish an approximate equivalence between a generalised quantum Rabi
model and its nth order counterparts where spin-boson interactions are
nonlinear as they comprise a simultaneous exchange of bosonic excitations.
Although there exists no unitary transformation between these models, we
demonstrate their equivalence to a good approximation in a wide range of
parameters. This shows that nonlinear spin-boson couplings, i.e. nth order
quantum Rabi models, are accessible to quantum systems with only linear
coupling between boson and spin modes by simply adding spin rotations and after
an appropriate transformation. Furthermore, our result prompts novel
approximate analytical solutions to the dynamics of the quantum Rabi model in
the ultrastrong coupling regime improving previous approaches.Comment: 9 pages, 3 figures plus Supplemental Informatio