Regensburg 2019 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 49: Poster Session: Superconductivity
TT 49.46: Poster
Wednesday, April 3, 2019, 15:00–18:30, Poster D
Gauge dependence of the two-level approximation in circuit QED — •Marco Roth1,2, David DiVincenzo1,2, and Fabian Hassler1 — 1Institute for Quantum Information, RWTH Aachen University, 52056 Aachen, Germany — 2JARA Institute for Quantum Information (PGI-11), Forschungszentrum Jülich, 52428 Jülich, Germany
The Rabi model describes a qubit coupled to a single bosonic degree of freedom. In circuit QED, the qubit is usually obtained by projecting an anharmonic oscillator onto its two lowest eigenstates. This two-level approximation breaks the gauge invariance of the full-system Hamiltonian and results in gauge dependent Rabi models. Although the gauge invariance can be restored by block-diagonalizing the full Hamiltonian prior to the projection, this approach yields a strongly dressed model which lacks the physical interpretability of the Rabi model. We thus perform the block diagonalization perturbatively and investigate the gauge-related effects on different qubits. We find that in many cases, one can find a gauge that requires only a small number of perturbative terms to achieve good agreement between approximated and full Hamiltonian.