Publication: Nonequilibrium and nonperturbative dynamics of ultrastrong coupling in open lines
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Amer Physical Soc
The time and space resolved dynamics of a qubit with an Ohmic coupling to propagating 1D photons is studied, from weak coupling to the ultrastrong coupling regime. A nonperturbative study based on matrix product states shows the following results, (i) The ground state of the combined systems contains excitations of both the qubit and the surrounding bosonic field. (ii) An initially excited qubit equilibrates through spontaneous emission to a state, which under certain conditions is locally close to that ground state, both in the qubit and the field. (iii) The resonances of the combined qubit-photon system match those of the spontaneous emission process and also the predictions of the adiabatic renormalization [A. J. Leggett et al., Rev. Mod. Phys. 59, 1 (1987)]. Finally, nonperturbative ab initio calculations show that this physics can be studied using a flux qubit galvanically coupled to a superconducting transmission line.
© American Physical Society. The authors acknowledge support from the European project PROMISCE, Spanish MINECO projects FIS2011-25167 and FIS2012-33022, CAM research consortium QUITEMAD (S2009-ESP-1594), and Spanish Ramon y Cajal program.