article published yes Johannes M Fink author 4B591CBA-F248-11E8-B48F-1D18A9856A870000-0001-8112-028X András Dombi author András Vukics author Andreas Wallraff author Peter Domokos author JoFi department Nonequilibrium phase transitions exist in damped-driven open quantum systems when the continuous tuning of an external parameter leads to a transition between two robust steady states. In second-order transitions this change is abrupt at a critical point, whereas in first-order transitions the two phases can coexist in a critical hysteresis domain. Here, we report the observation of a first-order dissipative quantum phase transition in a driven circuit quantum electrodynamics system. It takes place when the photon blockade of the driven cavity-atom system is broken by increasing the drive power. The observed experimental signature is a bimodal phase space distribution with varying weights controlled by the drive strength. Our measurements show an improved stabilization of the classical attractors up to the millisecond range when the size of the quantum system is increased from one to three artificial atoms. The formation of such robust pointer states could be used for new quantum measurement schemes or to investigate multiphoton phases of finite-size, nonlinear, open quantum systems. https://research-explorer.ista.ac.at/download/1114/4972/IST-2017-753-v1+1_PhysRevX.7.011012.pdf application/pdfno American Physical Society2017 eng 2160-3308 00039745050000110.1103/PhysRevX.7.011012 71 J. M. Fink, A. Dombi, A. Vukics, A. Wallraff, and P. Domokos, “Observation of the photon blockade breakdown phase transition,” <i>Physical Review X</i>, vol. 7, no. 1. American Physical Society, 2017. Fink JM, Dombi A, Vukics A, Wallraff A, Domokos P. 2017. Observation of the photon blockade breakdown phase transition. Physical Review X. 7(1), 011012. Fink, Johannes M, András Dombi, András Vukics, Andreas Wallraff, and Peter Domokos. “Observation of the Photon Blockade Breakdown Phase Transition.” <i>Physical Review X</i>. American Physical Society, 2017. <a href="https://doi.org/10.1103/PhysRevX.7.011012">https://doi.org/10.1103/PhysRevX.7.011012</a>. Fink, Johannes M., et al. “Observation of the Photon Blockade Breakdown Phase Transition.” <i>Physical Review X</i>, vol. 7, no. 1, 011012, American Physical Society, 2017, doi:<a href="https://doi.org/10.1103/PhysRevX.7.011012">10.1103/PhysRevX.7.011012</a>. J.M. Fink, A. Dombi, A. Vukics, A. Wallraff, P. Domokos, Physical Review X 7 (2017). Fink JM, Dombi A, Vukics A, Wallraff A, Domokos P. Observation of the photon blockade breakdown phase transition. <i>Physical Review X</i>. 2017;7(1). doi:<a href="https://doi.org/10.1103/PhysRevX.7.011012">10.1103/PhysRevX.7.011012</a> Fink, J. M., Dombi, A., Vukics, A., Wallraff, A., &#38; Domokos, P. (2017). Observation of the photon blockade breakdown phase transition. <i>Physical Review X</i>. American Physical Society. <a href="https://doi.org/10.1103/PhysRevX.7.011012">https://doi.org/10.1103/PhysRevX.7.011012</a> 11142018-12-11T11:50:13Z2025-07-10T11:50:07Z