Universal fluctuations and squeezing in generalized Dicke model near the superradiant phase transition
Autor: | Shapiro, D. S., Pogosov, W. V., Lozovik, Yu. E. |
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Rok vydání: | 2019 |
Předmět: | |
Zdroj: | Phys. Rev. A 102, 023703 (2020) |
Druh dokumentu: | Working Paper |
DOI: | 10.1103/PhysRevA.102.023703 |
Popis: | In a view of recent proposals for the realization of anisotropic light-matter interaction in such platforms as (i) non-stationary or inductively and capacitively coupled superconducting qubits, (ii) atoms in crossed fields and (iii) semiconductor heterostructures with spin-orbital interaction, the concept of generalized Dicke model, where coupling strengths of rotating wave and counter-rotating wave terms are unequal, has attracted great interest. For this model, we study photon fluctuations in the critical region of normal-to-superradiant phase transition when both the temperatures and numbers of two-level systems are finite. In this case, the superradiant quantum phase transition is changed to a fluctuational region in the phase diagram that reveals two types of critical behaviors. These are regimes of Dicke model (with discrete $\mathbb{Z}_2$ symmetry), and that of (anti-) and Tavis-Cummings $U(1)$ models. We show that squeezing parameters of photon condensate in these regimes show distinct temperature scalings. Besides, relative fluctuations of photon number take universal values. We also find a temperature scales below which one approaches zero-temperature quantum phase transition where quantum fluctuations dominate. Our effective theory is provided by a non-Goldstone functional for condensate mode and by Majorana representation of Pauli operators. We also discuss Bethe ansatz solution for integrable $U(1)$ limits. Comment: 17 pages, 7 figures, 1 table. Substantial revisions made, the title changed. The version accepted in Phys. Rev. A |
Databáze: | arXiv |
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