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Genuine Quantum Effects in Dicke-Type Models at Large Atom Numbers
1TUD Dresden University of Technology, Institute of Theoretical Physics, 01062, Dresden, Germany.
Physical Review Letters
|October 5, 2025
Summary
Genuine quantum effects persist in unbalanced open Dicke models with mesoscopic atom numbers. This contrasts with balanced models where these effects vanish as atom numbers increase, revealing non-commuting limits in quantum many-body systems.
Area of Science:
- Quantum physics
- Quantum many-body systems
- Open quantum systems
Background:
- Dicke models describe collective quantum phenomena in systems with many atoms.
- Mean-field theory often predicts system behavior in the thermodynamic limit (N→∞).
- Recent experiments realize driven and dissipative quantum many-body systems using ultracold gases in optical cavities.
Purpose of the Study:
- To investigate quantum effects beyond mean-field predictions in open Dicke models.
- To explore the influence of atom number (N) on these quantum effects.
- To identify conditions where genuine quantum phenomena survive for large, finite N.
Main Methods:
- Numerical investigation of balanced and unbalanced open Dicke models.
- Application of a novel open-system dynamics method for exact quantum dynamical results.
- Analysis of systems with atom numbers up to a mesoscopic N≈1000.
Main Results:
- Beyond-mean-field effects diminish rapidly with increasing N in the balanced Dicke model.
- Parameter regimes in the unbalanced Dicke model identified where quantum effects persist for mesoscopic N.
- Observed quantum effects include strong steady-state squeezing and modified phase diagrams absent in mean-field descriptions.
Conclusions:
- The steady-state limit and thermodynamic limit do not commute for these systems.
- Genuine quantum effects can survive in mesoscopic systems under specific conditions in unbalanced Dicke models.
- Mean-field descriptions are insufficient for capturing all quantum phenomena in large, finite open quantum systems.
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