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Section: New Results

Escape of a Driven Quantum Josephson Circuit into Unconfined States

Participants: Raphaël Lescanne, Zaki Leghtas, Mazyar Mirrahimi and Lucas Verney

Josephson circuits have been ideal systems to study complex nonlinear dynamics that can lead to chaotic behavior and instabilities. More recently, Josephson circuits in the quantum regime, particularly in the presence of microwave drives, have demonstrated their ability to emulate a variety of Hamiltonians that are useful for the processing of quantum information. In this work, we show that these drives lead to an instability that results in the escape of the circuit mode into states that are not confined by the Josephson cosine potential. We observe this escape in a ubiquitous circuit: a transmon embedded in a 3D cavity. When the transmon occupies these free-particle-like states, the circuit behaves as though the junction had been removed and all nonlinearities are lost. This work deepens our understanding of strongly driven Josephson circuits, which is important for fundamental and application perspectives, such as the engineering of Hamiltonians by parametric pumping. This experimental work published in [17] demonstrates elements of the theory derived by [22].