Depolarization shift of the superradiant phase transition

Grießer, Tobias; Vukics, András; Domokos, P.

doi:10.1103/physreva.94.033815

Cited by 31 publications

(51 citation statements)

References 27 publications

(50 reference statements)

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“…By considering a full description of a realistic system of atoms in a real cavity, refs. [35][36][37][38][39] showed that a phase transition can occur in the right geometry. Since the "photon creation" operator describes different physical fields in different gauges, it is important to check what physical fields acquire macroscopic expectations in such a transition.…”

Section: Other Realizations Of the Dicke Modelmentioning

confidence: 99%

Introduction to the Dicke Model: From Equilibrium to Nonequilibrium, and Vice Versa

et al. 2018

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The Dicke model describes the coupling between a quantized cavity field and a large ensemble of two‐level atoms. When the number of atoms tends to infinity, this model can undergo a transition to a superradiant phase, belonging to the mean‐field Ising universality class. The superradiant transition was first predicted for atoms in thermal equilibrium and was recently realized with a quantum simulator made of atoms in an optical cavity, subject to both dissipation and driving. This progress report offers an introduction to some theoretical concepts relevant to the Dicke model, reviewing the critical properties of the superradiant phase transition and the distinction between equilibrium and nonequilibrium conditions. In addition, it explains the fundamental difference between the superradiant phase transition and the more common lasing transition. This report mostly focuses on the steady states of atoms in single‐mode optical cavities, but it also mentions some aspects of real‐time dynamics, as well as other quantum simulators, including superconducting qubits, trapped ions, and using spin–orbit coupling for cold atoms. These realizations differ in regard to whether they describe equilibrium or nonequilibrium systems.

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Section: Other Realizations Of the Dicke Modelmentioning

confidence: 99%

Introduction to the Dicke Model: From Equilibrium to Nonequilibrium, and Vice Versa

et al. 2018

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“…As indicated in the main text, we perform the HolsteinPrimakoff transformation, as well as the transformation (12)(13)(14), and we consider the case β = 0:b = β +d =d. This gives us for the Hamiltonian:…”

Section: Appendix A: Linear Term Expansion Of the Hamiltonianmentioning

confidence: 99%

“…In the limit of a large number of qubits, the DM undergoes a SPT [5] in the ultrastrong coupling (USC) regime, where the collective light-matter coupling becomes comparable to the qubit and field bare frequencies [6]. Although the DM is commonly used to describe atomic and solid-state systems, whether it provides a reliable description of the system ground state when approaching the critical coupling is still the subject of debate [7][8][9][10][11][12][13]. In particular, the presence of the so-called diamagnatic term is expected to prevent the SPT.…”

Section: Introductionmentioning

confidence: 99%

Superradiant phase transition in the ultrastrong-coupling regime of the two-photon Dicke model

et al. 2017

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The controllability of current quantum technologies allows to implement spin-boson models where two-photon couplings are the dominating terms of light-matter interaction. In this case, when the coupling strength becomes comparable with the characteristic frequencies, a spectral collapse can take place, i.e. the discrete system spectrum can collapse into a continuous band. Here, we analyze the thermodynamic limit of the two-photon Dicke model, which describes the interaction of an ensemble of qubits with a single bosonic mode. We find that there exists a parameter regime where two-photon interactions induce a superradiant phase transition, before the spectral collapse occurs. Furthermore, we extend the mean-field analysis by considering second-order quantum fluctuations terms, in order to analyze the low-energy spectrum and compare the critical behavior with the one-photon case.

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“…(2) [21,22]. Counter examples against that no-go theorem are still being discussed even in the cur-rent literature [23,24]. However, the thermal SRPT has not yet been realized experimentally, while its nonequilibrium analogue has been demonstrated in cold atoms [25], and a thermal-equilibrium analogue has been theoretically proposed in an artificial system composed of a superconducting circuit [26].…”

Section: (A) (B)mentioning

confidence: 99%

“…While the presence of a thermal SRPT in the minimal-coupling Hamiltonian (derived from the Maxwell equations and Newton's equation of charged particles feeling the Lorentz force) in Eq. (2) is still under debate [21][22][23][24], there remains a possibility for realizing a thermal SRPT in systems where spins, instead of charges, interact with the EM fields, as pointed out by Knight et al in 1978 [31]. A hint of such a possibility lies in certain magnetic phase transitions, which are caused by interactions between two species of spins within the same material.…”

Section: (A) (B)mentioning

confidence: 99%

Terahertz strong-field physics without a strong external terahertz field

Bamba

Kono

2019

Ultrafast Phenomena and Nanophotonics XXIII

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Traditionally, strong-field physics explores phenomena in matter (atoms, molecules, and solids) driven by an extremely strong laser field nonperturbatively. However, even in the complete absence of an external electromagnetic field, strong-field phenomena can arise when matter strongly couples with the zero-point field of the quantum vacuum state, i.e., fluctuating electromagnetic waves whose expectation value is zero. Some of the most striking examples of this occur in a cavity setting, in which an ensemble of two-level atoms resonantly interacts with a single photonic mode of vacuum fields, producing vacuum Rabi splitting. In particular, the nature of the matter-vacuum-field coupled system fundamentally changes when the coupling rate (equal to one half of the vacuum Rabi splitting) becomes comparable to, or larger than, the resonance frequency. In this so-called ultrastrong coupling regime, a non-negligible number of photons exist in the ground state of the coupled system. Furthermore, the coupling rate can be cooperatively enhanced (via so-called Dicke cooperativity) when the matter is comprised of a large number of identical two-level particles, and a quantum phase transition is predicted to occur as the coupling rate reaches a critical value. Low-energy electronic or magnetic transitions in many-body condensed matter systems with large dipole moments are ideally suited for searching for these predicted phenomena. Here, we discuss two condensed matter systems that have shown cooperative ultrastrong interactions in the terahertz frequency range: a Landau-quantized two-dimensional electron gas interacting with high-quality-factor cavity photons, and an Er 3+ spin ensemble interacting with Fe 3+ magnons in ErFeO3.

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Depolarization shift of the superradiant phase transition

Cited by 31 publications

References 27 publications

Introduction to the Dicke Model: From Equilibrium to Nonequilibrium, and Vice Versa

Introduction to the Dicke Model: From Equilibrium to Nonequilibrium, and Vice Versa

Superradiant phase transition in the ultrastrong-coupling regime of the two-photon Dicke model

Terahertz strong-field physics without a strong external terahertz field

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