Nonequilibrium and nonperturbative dynamics of ultrastrong coupling in open lines.
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.
Instituto de Física Fundamental IFF-CSIC, Calle Serrano 113b, Madrid E-28006, Spain.
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Peropadre
Instituto de Ciencia de Materiales de Aragón y Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, Zaragoza E-50009, Spain and Fundación ARAID, Paseo María Agustín 36, Zaragoza E-50004, Spain.
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Zueco
Facultad de CC. Físicas, Universidad Complutense de Madrid, Madrid E-28040, Spain and Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH, United Kingdom.
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Porras
Instituto de Física Fundamental IFF-CSIC, Calle Serrano 113b, Madrid E-28006, Spain.
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García-Ripoll