Fundamental limitation of ultrastrong coupling between light and atoms

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

doi:10.1103/physreva.92.043835

Cited by 35 publications

(56 citation statements)

References 28 publications

(46 reference statements)

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“…Let us recall again the assumptions which allow the minimal coupling Hamiltonian to be transformed to the above form (for details see Ref. [14] and the Appendix). One condition is that we consider only states where the internal energy of any given atom is low.…”

Section: Regularized Electric Dipole Gaugementioning

confidence: 99%

“…The RED gauge can be obtained from the standard minimal coupling gauge by canonical transformation [14] as shown in the Appendix. The Hamiltonian then reads…”

Section: Regularized Electric Dipole Gaugementioning

confidence: 99%

“…That is, the superradiant criticality is achieved at an atom gas density very close to the crystalline density of the given atomic species. One can even conjecture that the superradiant phase transition is nothing else but the image of conden- * Electronic address: vukics.andras@wigner.mta.hu sation (liquefaction or solidification/crystallization, depending on the species) within the simplified framework of dipolar quantum electrodynamics [14]. The formation of covalent bonds between atoms requires a refined description of the higher-than-dipole multipolar terms, of course, but the criticality itself can be indicated in a much simpler model such as the dipole Hamiltonian.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, the condition of spatially separated atoms should be released in order to investigate the radiative properties of the ensemble at the high densities considered. In this regime, the instantaneous -depolarizing -atom-atom interaction, whose range in the RED gauge is reduced to the atomic size scale [14], plays a substantial role, and is expected to shift the critical point. The physical reason of the expected shift is obvious: assume that the atoms are spontaneously polarized along a given direction in the superradiant phase.…”

Section: Introductionmentioning

confidence: 99%

“…However, the validity of the Dicke model is, in fact, surprisingly robust in treating the interaction between radiation and matter [12,13]. One can define a gauge transformation from the minimal coupling Hamiltonian -the a priori model of atomic QED -to a regularized electric-dipole (RED) coupling Hamiltonian [14] which is suitable to describe the coupling between independent atoms and well-defined modes of the radiation field, and which can then be systematically truncated to the simple form of the Dicke model.…”

Section: Introductionmentioning

confidence: 99%

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Depolarization shift of the superradiant phase transition

2016

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We investigate the possibility of a Dicke-type superradiant phase transition of an atomic gas with an extended model which takes into account the short-range depolarizing interactions between atoms approaching each other as close as the atomic size scale, which interaction appears in a regularized electric-dipole picture of the QED of atoms. By using a mean field model, we find that a critical density does indeed exist, though the atom-atom contact interaction shifts it to a higher value than it can be obtained from the bare Dicke-model. We argue that the system, at the critical density, transitions to the condensed rather than the "superradiant" phase.

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Section: Regularized Electric Dipole Gaugementioning

confidence: 99%

“…The RED gauge can be obtained from the standard minimal coupling gauge by canonical transformation [14] as shown in the Appendix. The Hamiltonian then reads…”

Section: Regularized Electric Dipole Gaugementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Depolarization shift of the superradiant phase transition

2016

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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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Theoretical Methods for Ultrastrong Light–Matter Interactions

Boité

2020

Adv Quantum Tech

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This article reviews theoretical methods developed in the last decade to understand cavity quantum electrodynamics in the ultrastrong-coupling regime, where the strength of the light-matter interaction becomes comparable to the photon frequency. Along with profound modifications of fundamental quantum optical effects giving rise to a rich phenomenology, this regime introduces significant theoretical challenges. One of the most important is the break-down of the rotating-wave approximation which neglects all non-resonant terms in lightmatter interaction Hamiltonians. Consequently, a large part of the quantum optical theoretical framework has to be revisited in order to accurately account for all interaction terms in this regime. We give in this article a broad overview of the recent progress, ranging from analytical estimates of ground-state properties to proper derivations of master equations and computation of photodetection signals. For each aspect of the theory, the basic principles of the methods are illustrated on paradigmatic models such as quantum Rabi and spin-boson models. In this spirit, most of the article is devoted to effective models, relevant for the various experimental platforms in which the ultrastrong coupling has been reached, such as semiconductor microcavities and superconducting circuits. The validity of these models is discussed in the last part of the article, where we address recent debates on fundamental issues related to gauge invariance in the ultrastrong-coupling regime.

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Fundamental limitation of ultrastrong coupling between light and atoms

Cited by 35 publications

References 28 publications

Depolarization shift of the superradiant phase transition

Depolarization shift of the superradiant phase transition

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

Theoretical Methods for Ultrastrong Light–Matter Interactions

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