Ultrastrong coupling between light and matter

By Anton Frisk Kockum, Adam Miranowicz, S. De Liberato, Salvatore Savasta, Franco Nori. Nature Reviews Physics, 2018

1,476 citations recorded by the source corpus.

Light–matter coupling with strength comparable to the bare transition frequencies of the system is called ultrastrong. This Review surveys how experiments have realized ultrastrong coupling in the past decade, the new phenomena predicted in this regime and the applications it enables. Ultrastrong coupling between light and matter has, in the past decade, transitioned from a theoretical idea to an experimental reality. It is a new regime of quantum light–matter interaction, which goes beyond weak and strong coupling to make the coupling strength comparable to the transition frequencies in the system. The achievement of weak and strong coupling has led to increased control of quantum systems and to applications such as lasers, quantum sensing, and quantum information processing. Here we review the theory of quantum systems with ultrastrong coupling, discussing entangled ground states with virtual excitations, new avenues for nonlinear optics, and connections to several important physical models. We also overview the multitude of experimental setups, including superconducting circuits, organic molecules, semiconductor polaritons, and optomechanical systems, that have now achieved ultrastrong coupling. We conclude by discussing the many potential applications that these achievements enable in physics and chemistry. Ultrastrong coupling (USC) can be achieved by coupling many dipoles to light, or by using degrees of freedom whose coupling is not bounded by the smallness of the fine-structure constant. The highest light–matter coupling strengths have been measured in experiments with Landau polaritons in semiconductor systems and in setups with superconducting quantum circuits. With USC, standard approximations break down, allowing processes that do not conserve the number of excitations in the system, leading to a ground state that contains virtual excitations. Potential applications of USC include fast and protected quantum information processing, nonlinear optics, modified chemical reactions and the enhancement of various quantum phenomena. Now that USC has been reached in several systems, it is time to experimentally explore the new phenomena predicted for this regime and to find their useful applications. Ultrastrong coupling (USC) can be achieved by coupling many dipoles to light, or by using degrees of freedom whose coupling is not bounded by the smallness of the fine-structure constant. The highest light–matter coupling strengths have been measured in experiments with Landau polaritons in semiconductor systems and in setups with superconducting quantum circuits. With USC, standard approximations break down, allowing processes that do not conserve the number of excitations in the system, leading to a ground state that contains virtual excitations. Potential applications of USC include fast and protected quantum information processing, nonlinear optics, modified chemical reactions and the enhancement of various quantum phenomena. Now that USC has been reached in several systems, it is time to experimentally explore the new phenomena predicted for this regime and to find their useful applications.

Subfields: Atomic and Molecular Physics, and Optics, Biomedical Engineering

View Paper: https://www.semanticscholar.org/paper/2e16d5efaeb1a685f46b0f2b571e697daf1eb3cd

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Citations in the corpus

Quantum simulation and computing with Rydberg-interacting qubits (2020, background): “Technology for microwave signal generation is very well developed and the large transition dipole moments of Rydberg states (scaling with n 2 ) enables fast quantum operations with modest microwave powers 142 , even reaching the ultrastrong coupling regime ( Ω > ω 0 ) 143 .”
Open quantum systems with local and collective incoherent processes: Efficient numerical simulations using permutational invariance (2018, neutral): “The rich phenomenology which becomes then observable [92, 96– 98, 240–259] has led to a remarkable interest in those nonperturbative regimes, which have been experimentally realized in a number of experimental implementations well described, at least in first approximation [260–264], by the Dicke mo”
Circuit quantum electrodynamics (2020, methodology): “The reader interested in learning more about this regime of lightmatter interaction can consult the reviews by Forn-Dı́az et al. (2019) and Frisk Kockum et al. (2019).”
Quantum Electrodynamics in a Topological Waveguide (2020, background): “Such an assumption is known to be valid when the coupling terms in the Hamiltonian are much smaller than the frequency scale of the uncoupled Hamiltonian Ĥ0 [69].”
Oscillating bound states for a giant atom (2019, background): “—The study of interaction between light and matter is one of the core topics in modern physics [1].”
Superconducting quantum computing: a review (2020, methodology): “[150] Kockum, A.”