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DESCRIPTION:Speaker: András Vukics\nhosted by Johannes Fink\nAbstract: A n
 onequilibrium phase transition in a damped-driven open quantum system is a
  transition between two robust steady states controlled by an external par
 ameter. In second-order transitions the change is abrupt at a critical poi
 nt\, whereas in first-order transitions the two phases can coexist in a cr
 itical hysteresis domain. Here\, I present a first-order dissipative quant
 um phase transition\, whose microscopic basis is that the photon blockade 
 in a driven Jaynes-Cummings system (single atom coupled to a single mode o
 f a resonator) is broken with increasing drive power [1\,2]. The observed 
 experimental signature is a bimodal phase-space distribution with varying 
 weights controlled by the drive strength. Alternatively\, in the time doma
 in\, a bistable signal is obtained\, with switching times separated by ord
 ers of magnitudes from any microscopic timescales of the system\, and reac
 hing up to seconds [3]. We identify a well-defined thermodynamic limit\, w
 here the bistability solution develops into the first-order phase transiti
 on. The bistability can be regarded as a finite-size signature of the phas
 e transition\, and we can calculate the finite-size scaling exponent numer
 ically [4]. Importantly\, even in the thermodynamic limit\, the stability 
 of phases originates from the discrete spectrum of the small quantum syste
 m\, the switching being induced by the continuous weak measurement of the 
 system by the environment. At the end of the talk\, I will sketch the simu
 lation tool used for these studies\, that is C++QED: a framework for simul
 ating open quantum dynamics [5\,6] conceived for supercomputing environmen
 ts.References: [1] A. Dombi et al. Eur. Phys. J. D 69\, 60 (2015) [2] H. J
 . Carmichael\, Phys. Rev. X 5\, 031028 (2015) [3] J. M. Fink et al. Phys. 
 Rev. X 7\, 011012 (2017) [4] A. Vukics et al. Quantum 3\, 150 (2019) [5] A
 . Vukics\, Comp. Phys. Comm. 183\, 1381-1396 (2012) [6] https://github.com
 /vukics/cppqed
LOCATION:Heinzel Seminar Room / Office Bldg West (I21.EG.101)\, ISTA
ORGANIZER:swiddman@ist.ac.at
SUMMARY:András Vukics: The breakdown of photon blockade: a first-order dis
 sipative quantum phase transition
URL:https://talks-calendar.ista.ac.at/events/3228
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