Light-matter strong coupling has been the subject of much attention in recent decades, giving optical systems unique features. However, properties of a system with strong coupling are determined by the properties of its components and are thus difficult to control. Here, we propose Floquet engineering, a technique of controlling the energy levels of a quantum system using external fields, as a method of manipulating a hybrid system of a molecule strongly coupled to a single-mode resonator. We show that an external field can change the relative positions of levels in an open strongly coupled system, leading to a change in the rates of transitions between them. We demonstrate that if the frequency of the pumping wave is close to polariton transitions in the hybrid system, nonmonotonic dependence of fluorescence and scattering amplitudes on pump intensity with a narrow resonance-like response occurs. We show that this phenomenon occurs due to hybridization of the lower and upper polaritons with substantially different excitation numbers caused by the pumping affecting polariton states of the system. This occurs when the Rabi interaction with the coherent field is comparable to the field-matter coupling constant, which in turn needs to be sufficient for the manifestation of strong coupling. This nonmonotonic dependence of the fluorescence and scattering amplitudes on pump rate intensity paves the way for the creation of nonlinear optical devices.
Light-matter strong coupling has been the subject of much attention in recent decades, giving optical systems unique features. However, properties of a system with strong coupling are determined by the properties of its components and are thus difficult to control. Here, we propose Floquet engineering, a technique of controlling the energy levels of a quantum system using external fields, as a method of manipulating a hybrid system of a molecule strongly coupled to a single-mode resonator. We show that an external field can change the relative positions of levels in an open strongly coupled system, leading to a change in the rates of transitions between them. We demonstrate that if the frequency of the pumping wave is close to polariton transitions in the hybrid system, nonmonotonic dependence of fluorescence and scattering amplitudes on pump intensity with a narrow resonance-like response occurs. We show that this phenomenon occurs due to hybridization of the lower and upper polaritons with substantially different excitation numbers caused by the pumping affecting polariton states of the system. This occurs when the Rabi interaction with the coherent field is comparable to the field-matter coupling constant, which in turn needs to be sufficient for the manifestation of strong coupling. This nonmonotonic dependence of the fluorescence and scattering amplitudes on pump rate intensity paves the way for the creation of nonlinear optical devices.
We discover an unexpected behavior in a hybrid system composed of cavity strongly coupled to molecules and subjected to high intensity coherent pumping. We show that if the frequency of the pumping wave is close to polariton transitions in the hybrid system, non monotone dependence of fluorescence and scattering amplitudes on pump intensity with a narrow resonance-like response occurs. We demonstrate that this phenomenon occurs due to hybridization of lower and upper polaritons with substantially different excitation numbers caused by the pumping affecting polariton states of the system. This occurs when the Rabi interaction with coherent field is comparable to the field-matter coupling constant which in turn needs to be sufficient for the manifestation of strong coupling. This non-monotonic dependence of the fluorescence and scattering amplitudes on pump rate intensity pave the way for creation of nonlinear optical devices.
Resonance interaction between a molecular transition and a confined electromagnetic field can reach the coupling regime where coherent exchange of energy between light and matter becomes reversible. In this case, two new hybrid states separated in energy are formed instead of independent eigenstates, which is known as Rabi splitting. This modification of the energy spectra of the system offers new possibilities for controlled impact on various fundamental properties of coupled matter (such as the rate of chemical reactions and the conductivity of organic semiconductors). To date, the strong coupling regime has been demonstrated in many configurations under different ambient conditions. However, there is still no comprehensive approach to determining parameters for achieving the strong coupling regime for a wide range of practical applications. In this review, a detailed analysis of various systems and corresponding conditions for reaching strong coupling is carried out and their advantages and disadvantages, as well as the prospects for application, are considered. The review also summarizes recent experiments in which the strong coupling regime has led to new interesting results, such as the possibility of collective strong coupling between X-rays and matter excitation in a periodic array of Fe isotopes, which extends the applications of quantum optics; a strong amplification of the Raman scattering signal from a coupled system, which can be used in surface-enhanced and tip-enhanced Raman spectroscopy; and more efficient second-harmonic generation from the low polaritonic state, which is promising for nonlinear optics. The results reviewed demonstrate great potential for further practical applications of strong coupling in the fields of photonics (low-threshold lasers), quantum communications (switches), and biophysics (molecular fingerprinting).
Field quantization is fundamental to quantum optics and polaritonic chemistry, enabling exploration of light–matter interactions at the quantum level. We report resonant coupling between the two-level excitation of a dinickel (Ni₂) complex and its locally recycled scattering field under ambient, cavity-free conditions. This Ni₂ system exhibits hallmark resonance-fluorescence features, including Rabi doublets and Mollow triplets, with strong coupling achieved under weak, non-resonant excitation. The Ni₂ unit functions as a diatomic resonator, enhancing photon scattering and forming a Jaynes–Cummings molecule. Simulations of second-order correlation functions confirm photon antibunching and underdamped Rabi oscillations. Collective coupling strength scales linearly with the number of molecules (N), surpassing Tavis–Cummings model predictions and reaching the ultrastrong coupling regime. These findings establish Ni₂ complexes as robust molecular quantum systems, offering a chemically tunable platform for quantum information processing and coherent chemical control at the molecular scale.
Strong light-matter coupling gives rise to polaritons - hybrid excitations whose mixed photonic and matter character enables control over optical, electronic and chemical properties. This Feature Article surveys the main architectures supporting polariton formation, including photonic microcavities, plasmonic nanostructures, open cavities and metasurfaces, and outlines how inorganic semiconductors, organic aggregates and hybrid systems access strong and ultrastrong coupling. Key phenomena such as coherent dynamics, vibronic interactions, dark-state reservoirs and polariton-mediated energy and electron transport are discussed, together with the experimental and theoretical tools used to study them. We highlight examples where strong coupling modifies charge transport, energy flow and chemical reactivity, and we summarize emerging regimes, including intermediate and dark-strong coupling, that broaden the landscape of hybrid light-matter physics.
Field quantization is fundamental to quantum optics and polaritonic chemistry, enabling exploration of light–matter interactions at the quantum level. We report resonant coupling between the two-level excitation of a dinickel (Ni₂) complex and its locally recycled scattering field under ambient, cavity-free conditions. This Ni₂ system exhibits hallmark resonance-fluorescence features, including Rabi doublets and Mollow triplets, with strong coupling achieved under weak, non-resonant excitation. The Ni₂ unit functions as a diatomic resonator, enhancing photon scattering and forming a Jaynes–Cummings molecule. Simulations of second-order correlation functions confirm photon antibunching and underdamped Rabi oscillations. Collective coupling strength scales linearly with the number of molecules (N), surpassing Tavis–Cummings model predictions and reaching the ultrastrong coupling regime. These findings establish Ni₂ complexes as robust molecular quantum systems, offering a chemically tunable platform for quantum information processing and coherent chemical control at the molecular scale.
Strong periodic driving of cavity-quantum electrodynamics (QED) in the ultrastrong-coupling regime creates nonequilibrium states whose dissipation is governed by Floquet quasienergies rather than undriven dressed resonances. However, modeling such a regime is a significant theoretical challenge, including a number of subtle problems such as the need to ensure gauge invariance for truncated matter-cavity systems with time-dependent driving. To fill this theoretical gap, we introduce a nonsecular Floquet generalized master equation framework for strongly driven open cavity-QED systems, formulated in the dressed basis of the quantum Rabi model and applicable to structured reservoirs without rotating-wave approximations. Our theory can thus model Floquet-driven dynamics in open ultrastrong-coupling cavity-QED, and demonstrates a wide range of quantum state control. Using strong optical pumping and parametric mechanical modulation, we compute long-time populations, fluorescence spectra, and the Floquet-Liouville eigenspectra, resolving observable resonances into hybridized quasienergy channels and decay rates. By systematically comparing with conventional time-independent dressed-basis generalized master equations, we show that static approaches only reproduce steady-state populations in restricted excitation regimes, and fail for frequency-resolved observables and break down under appropriate Floquet engineering, surprisingly, even for spectrally flat baths. Structured environments, such as Lorentzian-Ohmic reservoirs, further amplify these discrepancies through sideband-selective decay. Our results demonstrate that dissipation in driven ultrastrong cavity-QED is intrinsically quasienergy resolved and we establish Floquet-dissipative theory as an accurate and powerful framework for predicting spectra, controlling decay pathways, and engineering nonequilibrium quantum states and reservoirs.