Bonn 2025 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 5: Collective Effects and Disordered Systems
Q 5.8: Talk
Monday, March 10, 2025, 12:45–13:00, HS I PI
Disorder-dependent phases of optically deep atomic ensembles — •Kasper J. Kusmierek1, Max Schemmer2, Sahand Mahmoodian3, and Klemens Hammerer1 — 1ITP, Leibniz University Hannover, Germany — 2Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), Fiorentino, Italy — 3Centre for Engineered Quantum Systems, University of Sydney, Australian
The interaction of light with an ensemble of two-level systems in a one-dimensional geometry is commonly described by two key models of quantum electrodynamics (QED): the driven-dissipative Dicke model or the Maxwell-Bloch equations. Both exhibit distinct features of phase transitions and separations, depending on optical depth and drive strength. Using a parent spin model derived from bidirectional waveguide QED, we show these models arise as limits corresponding to small and large disorder in atomic positions. We numerically solve the mean-field equations and investigate the phase diagram depending on optical depth, drive strength, and disorder. For the unidirectional model we go beyond mean-field theory by performing a second-order cumulant expansion, complementing analytical mean-field results. Studying atomic inversion and light transmission, we find, in the thermodynamic limit, phase separation occurs with a critical value dependent on the degree of order but not on inhomogeneous broadening effects. Even far from the thermodynamic limit, this critical value marks a special point in the atomic correlation landscape of the unidirectional model. We conclude disordered effective one-dimensional systems can be modeled using unidirectional waveguide approaches.
Keywords: Waveguide QED; Phase Transition/ Separation; Disordered systems