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Ultrastrong coupling regimes of light-matter interaction (1804.09275v3)

Published 24 Apr 2018 in quant-ph and cond-mat.supr-con

Abstract: Recent experiments have demonstrated that light and matter can mix together to an extreme degree, and previously uncharted regimes of light-matter interactions are currently being explored in a variety of settings. The so-called ultrastrong coupling (USC) regime is established when the light-matter interaction energy is a comparable fraction of the bare frequencies of the uncoupled systems. Furthermore, when the interaction strengths become larger than the bare frequencies, the deep-strong coupling (DSC) regime emerges. This article reviews advances in the field of the USC and DSC regimes, in particular, for light modes confined in cavities interacting with two-level systems. An overview is first provided on the theoretical progress since the origins from the semiclassical Rabi model until recent developments of the quantum Rabi model. Next, several key experimental results from a variety of quantum platforms are described, including superconducting circuits, semiconductor quantum wells, and other hybrid quantum systems. Finally, anticipated applications are highlighted utilizing USC and DSC regimes, including novel quantum optical phenomena, quantum simulation, and quantum computation.

Citations (595)

Summary

  • The paper presents a comprehensive review of ultrastrong and deep strong coupling regimes, emphasizing the breakdown of the rotating wave approximation.
  • It details experimental validations including the Bloch-Siegert shift in superconducting circuits and advancements using semiconductor quantum wells.
  • The review outlines significant implications for quantum simulations, ultrafast quantum gates, and robust quantum communication systems.

Ultrastrong Coupling Regimes of Light-Matter Interaction

The paper "Ultrastrong coupling regimes of light-matter interaction" provides a comprehensive review of the theoretical and experimental advancements in the ultrastrong coupling (USC) and deep strong coupling (DSC) regimes between light and matter. These regimes are characterized by light-matter interaction energies that are comparable to or exceed the bare frequencies of the uncoupled systems. The paper highlights significant theoretical models, experimental achievements, and potential applications associated with these coupling regimes.

The USC regime is of particular interest due to the breakdown of the rotating wave approximation (RWA), which has traditionally simplified the analysis of quantum light-matter interactions. In this regime, counterrotating terms that are typically neglected become relevant, leading to novel quantum phenomena. The paper traces the development of this field from the semiclassical Rabi model to the quantum Rabi model (QRM), emphasizing the relevance of the QRM in both theoretical and applied physics domains. These developments have paved the way for experimental realizations across various quantum platforms, including superconducting circuits, semiconductor quantum wells, and hybrid quantum systems.

One of the notable theoretical advances discussed is the understanding of the ground state in the USC regime, which is a squeezed vacuum state containing a finite number of photons and atomic excitations. This understanding has been crucial for experiments that aim to tap into the quantum optical phenomena enabled by the USC regime, such as the generation of correlated photon pairs from the ground state.

Experimentally, superconducting quantum circuits have been at the forefront, achieving significant progress in probing the USC and DSC regimes. Noteworthy achievements include the first observations of the breakdown of the RWA and the Bloch-Siegert shift, which have confirmed the theoretical predictions made about the USC regime. These circuits have been instrumental in demonstrating large light-matter interaction strengths via various configurations, such as galvanic and capacitive couplings. In particular, the work by Yoshihara et al. broke new ground by reaching coupling strengths well into the DSC regime.

The paper also highlights the role of semiconductor quantum wells, specifically those exploiting intersubband polaritons and cyclotron resonances, in achieving the USC regime. Advances in metamaterial designs have allowed for the confinement of electromagnetic fields further, thus enhancing the interaction strength. Key results have been reported where normal mode splitting and vacuum Rabi splitting indicate the achievement of the USC regime.

The implications of achieving these coupling regimes are profound. For instance, they open new avenues for quantum simulations and computing, particularly in realizing ultrafast quantum gates and designing protected qubits. The ability to engineer and manipulate light-matter interactions at these extreme levels could lead to the development of novel quantum technologies, including more robust quantum communication systems and advanced quantum sensors.

Looking forward, the exploration of these extreme coupling regimes continues to be a dynamic and rapidly evolving field. Theoretical models are being expanded to accommodate more complex interactions and multiple modes, while experimental techniques are being refined to push the boundaries of achievable coupling strengths further. The integration of USC and DSC phenomena into practical applications remains a key focus, promising to revolutionize various aspects of quantum technology.

Overall, the detailed exposition of USC and DSC regimes in this paper underscores their central role in advancing our understanding of light-matter interactions and their potential in the burgeoning field of quantum technology. The interplay between theoretical predictions and experimental realizations continues to drive the field toward new discoveries and applications.