Spectral kissing and its dynamical consequences in the squeeze-driven Kerr oscillator
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Chávez-Carlos, J., Lezama, T.L.M., Cortiñas, R.G. et al. Spectral kissing and its dynamical consequences in the squeeze-driven Kerr oscillator. npj Quantum Inf 9, 76 (2023). [https://doi.org/10.1038/s41534-023-00745-1]
SponsorshipNSF CCI grant (Award Number 2124511); NSF grant No. DMR-1936006; I+D+i project PID2019-104002GB-C21 (MCIN/AEI/10.13039/501100-011033); The Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía; European Regional Development Fund (ERDF), ref. UHU-1262561; The CEAFMC and Universidad de Huelva High Performance Computer (HPC@UHU); The Campus Universitario el Carmen and funded by FEDER/MINECO project UNHU-15CE-2848; The MPS Simons Foundation Award ID: 678586
Transmon qubits are the predominant element in circuit-based quantum information processing, such as existing quantum computers, due to their controllability and ease of engineering implementation. But more than qubits, transmons are multilevel nonlinear oscillators that can be used to investigate fundamental physics questions. Here, they are explored as simulators of excited state quantum phase transitions (ESQPTs), which are generalizations of quantum phase transitions to excited states. We show that the spectral kissing (coalescence of pairs of energy levels) experimentally observed in the effective Hamiltonian of a driven SNAIL-transmon is an ESQPT precursor. We explore the dynamical consequences of the ESQPT, which include the exponential growth of out-of-time-ordered correlators, followed by periodic revivals, and the slow evolution of the survival probability due to localization. These signatures of ESQPT are within reach for current superconducting circuits platforms and are of interest to experiments with cold atoms and ion traps.