Speaker
Description
I present the relatively recent concept of first-order dissipative phase transitions that can occur in meso- and even microscopic quantum systems. One of the first examples of this phenomenology was the photon-blockade breakdown (PBB) effect, that occurs most simply in a coupled system of a bosonic mode and a qubit. For PBB, an abstract thermodynamic limit has been identified [1], where the coupling between the subsystems goes to infinity without affecting the system size (hence the designation zero-dimensional), and this limit was studied in a finite-size scaling approach [2], with scaling exponents determined numerically. Upon discussing the microscopic mechanism and the fully quantum solution, I will assess the neo- and semiclassical models, and the connection with optical bistability.
I describe the experimental studies: PBB was first observed in a circuit QED system [3], and the thermodynamic limit could also be modeled on this platform with a bespoke device [4]. The numerical modelling of this latter set of experiments highlighted the role of the higher lying transmon levels and the phase noise.
On the computational front, I present the extensive numerical studies (taking cca. 100 CPU years) performed with the C++QED simulation framework [5] in an OpenStack cloud environment.
[1] H. J. Carmichael, Phys. Rev. X 5, 031028 (2015).
[2] A. Vukics, A. Dombi, J. M. Fink, P. Domokos, Quantum 3, 150 (2019).
[3] J. M. Fink, A. Dombi, A. Vukics, A. Wallraff, and P. Domokos, Phys. Rev. X 7, 011012 (2017).
[4] R. Sett, F. Hassani, D. Phan, Sh. Barzanjeh, A. Vukics, and J. M. Fink, arXiv:2210.14182 (2022).
[5] https://github.com/vukics/cppqed
