Nonlinear optical responses of exciton—microcavity coupled system in weak and intermediate coupling regime

We introduce a new drift model for slow environmental perturbation affecting modal coupling in optical multi-mode fibers. This model preserves the mode coupling strength asymmetries characteristic to mode pairs of different mode groups while decorrelating the fiber transmission matrix. Existing drift models were derived for the strong coupling regime, in which case the coupling matrix elements are identically distributed, and not suitable for the weak to intermediate coupling regime as shown here. The models' impact on the inherent crosstalk characteristic of a fiber were evaluated for all linear coupling regimes and for fibers with up to 42 spatial and polarization modes. Moreover, transmission performance of 32 GBd 16-QAM (per polarization mode) over the dynamic channel is studied considering singular value decomposition (SVD) pre-coding for the multiple-input multiple-output multi-mode fiber channel. The impact of slow drift on channel equalization performance is evaluated in terms of residual crosstalk. A large discrepancy is observed for fiber channels in the weak and intermediate coupling regimes, while converging in the strong coupling regime. Furthermore, we show that 2 × 1 multiple-input single-output equalizers can be sufficient to compensate for the residual crosstalk in the weak to intermediate linear coupling regime and achieve optimal performance.

We consider two like-charged planar surfaces immersed in solution of oppositely charged dimer counterions with a bond length l. To analyze this system, we extend and employ a self-consistent field theory that has been shown to be accurate from the weak to the intermediate through to the strong coupling regimes. In the limit of very short dimers, the results converge to the results for pointlike divalent ions. Near the surfaces, the dimers lie parallel to the charged plates. In the intermediate coupling regime, the dimers are aligned perpendicularly to the surface when they are a distance l from a surface. In the weak coupling regime, the interactions are only repulsive. At slightly higher couplings, there is a minimum in the variation of the free energy with distance at approximately the bond length of the dimers, which arises from bridging conformations of the dimers. In the intermediate coupling regime, an additional minimum in the free energy is observed at much smaller distances, which is due to the correlations between the dimers. For large dimer bond lengths, this minimum is metastable with respect to the previous minimum. However, as the bond length decreases, this minimum becomes the stable, while the minimum associated with the dimer bond length becomes metastable and eventually disappears. For shorter dimer bond length the attractive interaction is the result of correlations between counterions and charges on the surfaces. We find that dimers can mediate attractive interaction between like-charged surfaces in the intermediate coupling regime. The analysis of orientations confirms the bridging mechanism for sufficiently long dimers, whereas at high electrostatic couplings charge correlations contribute to the attraction.

We investigate the plasma enhancement of nuclear reactions in the intermediate coupling regime using orbital free molecular dynamics (OFMD) simulations. Mixtures of H-Cu and H-Ag serve as prototypes of simultaneous weak and strong couplings due to the charge asymmetry. Of particular importance is the partial ionization of Cu and Ag and the free electron polarization captured by OFMD simulations. By comparing a series of OFMD simulations at various concentrations and constant pressure to multi-component hyper-netted chain (MCHNC) calculations of effective binary ionic mixtures, we set a general procedure for computing enhancement factors. The MCHNC procedure allows extension to very low concentrations (5% or less) and to very high temperatures (few keV) unreachable by the simulations. Enhancement factors for nuclear reaction rates extracted from the MCHNC approach are compared with the Salpeter theory in the weak and strong coupling regimes, and a new interpolation is proposed.

A relation is found between pulsed measurements of the excited-state probability of a two-level atom illuminated by a driving laser and a continuous measurement by a second laser coupling the excited state to a third state which decays rapidly and irreversibly. We find the time between pulses to achieve the same average detection time as a given continuous measurement in strong, weak or intermediate coupling regimes, generalizing the results of Schulman (1998 Phys. Rev. A 57 1509).

All-dielectric photonic crystals or metasurfaces supporting optical bound states in the continuum (BIC) are emerging as a promising platform for the study of light-matter interactions in the strong coupling regime. However, coupling of BIC to other optical excitations is generally weak, with the coupling strength limited in the range of several tens of milli electronvolts with short decoherence time. This greatly hinders their applications in solid-base quantum information devices that require a fast information exchange rate and long coherence time. Herein, a cavity-coupling strategy is used to extend the BIC-based coupling platforms. We propose a hybrid system containing an all-dielectric metasurface embedded in an optical microcavity, demonstrating the formation of BIC-cavity polaritons in the strong coupling regime with a surprisingly large Rabi splitting over 220 meV, far beyond the strong coupling regime. A flexible tuning of BIC-cavity coupling from weak to strong coupling regime is realized by controlling the shape of dielectric element of the metasurface. Importantly, a full quantum model based on Heisenberg-Langevin formalism reveals the temporal population dynamics of the coupling system, demonstrating the ultrafast Rabi socillation within 19 fs with a long decoherence time over 200 fs. Utilizing the multipolar expansion approach combined with full wave simulations, we also investigate the coupling-induced polariton characteristics in both the weak and strong coupling regimes. We find that the electric dipole component of the BIC mode dominates in the polariton states in weak coupling regime, which dramatically changes as the system is tuned into strong coupling regime. Such a cavity-coupling strategy in the present hybrid system is expected to be of great use for enhancing BIC-based light-matter interactions for more complex hybrid nanostructures such as three-mode systems with mixing BIC-cavity-exciton interactions.

A comprehensive picture of polaron and bipolaron physics is essential to understand the optical absorption spectrum in many materials with electron-phonon interactions. In particular, the finite-temperature properties are of interest since they play an important role in many experiments. Here, we combine the parallel two-site time-dependent variational principle algorithm (p2TDVP) with local basis optimization (LBO) and purification to calculate time-dependent current-current correlation functions. From this information, we extract the optical conductivity for the Holstein polaron and bipolaron with dispersive phonons at finite temperatures. For the polaron in the weak and intermediate electron-phonon coupling regimes, we analyze the influence of phonon dispersion relations on the spectra. For strong electron-phonon coupling, the known result of an asymmetric Gaussian is reproduced for a flat phonon band. For a finite phonon bandwidth, the center of the Gaussian is either shifted to larger or smaller frequencies, depending on the sign of the phonon hopping. We illustrate that this can be well understood by considering the Born-Oppenheimer surfaces. A similar behavior is seen for the bipolaron for strong coupling. For the bipolaron with weak and intermediate coupling strengths and a flat phonon band, we obtain two very different spectra. The latter also has a temperature-dependent resonance at a frequency below the phonon frequency.

We study Monte Carlo calculations of the effective potential for a scalar field theory using three techniques. One of these is a new method proposed and tested for the first time. In each case we extract the renormalised quantities of the theory. The system studied in our calculations is a one component $\phi^4$ model in two dimensions. We apply these methods to both the weak and strong coupling regime. In the weak coupling regime we compare our results for the renormalised quantities with those obtained from two-loop lattice perturbation theory. Our results are verified in the strong coupling regime through comparison with the strong coupling expansion. We conclude that effective potential methods, when suitably chosen, can be accurate tools in calculations of the renormalised parameters of scalar field theories.

Molecular photonic wires conduct electronic energy via their rapid transport properties. In photosynthesis, nature achieves efficient transport across large distances using delocalized excitons, generated by strong excitonic coupling between chromophores. How, or even whether, delocalization facilitates long-distance energy transport in synthetic systems has been challenging to experimentally test and optimize. Thus, far, studies have been limited to strongly coupled, heterogeneous chromophore aggregates or weakly coupled chromophore monomers. Here, we employed DNA nanostructures to engineer molecular photonic wires constructed from a series of excitonically coupled indocarbocyanine chromophores─achieving the intermediate and strong coupling regimes. Using time-resolved fluorescence spectroscopy and complementary simulations, we demonstrated that an intermediate intermolecular electronic coupling (∼kBT) enables up to 40% faster exciton transport as compared to strongly coupled chromophores. The delocalized excitons generated in the intermediate coupling regime exhibited properties conducive to rapid diffusivity, similar to their monomeric counterparts. Thus, intermediate excitonic coupling, analogous to natural systems, achieves long-distance exciton transport with the high chromophore density required for energy capture.

In this paper, we study the interaction between charged macroions (surfaces) immersed in a solution of oppositely charged, rod-like counterions and point-like co-ions. The system is modeled by a field theoretic approach, which was extended to treat mixtures of rod- and point-like ions. The theory is applicable from the weak to the intermediate through to the strong coupling regimes. In the weak coupling limit, the force between the charged surfaces are only repulsive. In the intermediate coupling regime, the rod-like ions can induce attractive force between the charged surfaces. In the strong coupling limit, the inter-ionic charge correlations dominate the attractive forces at short separations between the charged surfaces.

$J$-coupled nuclear magnetic resonance (NMR) spectroscopy in the strong coupling regime at low magnetic field ($10{}^{\ensuremath{-}7}$ T $lBl{10}^{\ensuremath{-}3}$ T) is more complex than at high field ($Bg{10}^{\ensuremath{-}3}$ T) and at ultralow field ($Bl{10}^{\ensuremath{-}7}$ T). We show that several upper and lower boundaries ${B}_{i}^{\mathrm{up}}$ and ${B}_{i}^{\mathrm{low}}$ of the magnetic field $B$ exist, where the complexity of $J$-coupled NMR spectra changes in terms of the number of lines. The index $i=1,2,\dots{}$ for ${B}_{i}^{\mathrm{up}}$ at high field specifies the perturbation order of the dominating Zeeman interaction and for ${B}_{i}^{\mathrm{low}}$ at ultralow field the perturbation order of the dominating $J$-coupling interaction. Mathematical expressions for these boundaries are derived for the case of a $J$-coupled $S$-$I$${}_{N}$ group where $S$ and $I$ are rare and abundant spins $\frac{1}{2}$ and $N$ counts the abundant spins $I$. The entire $B$-field range can further be delineated into two weak coupling regimes, one at high field with ${B}_{2}^{\mathrm{up}}lBl{B}_{1}^{\mathrm{up}}$ ($10{}^{\ensuremath{-}3}$ T $lBl{10}^{2}$ T), one at low field with ${B}_{1}^{\mathrm{low}}lBl{B}_{2}^{\mathrm{low}}({10}^{\ensuremath{-}8}$ T $lBl{10}^{\ensuremath{-}7}$ T), and a strong coupling regime with ${B}_{2}^{\mathrm{low}}lBl{B}_{2}^{\mathrm{up}}$ ($10{}^{\ensuremath{-}7}$ T $lBl{10}^{\ensuremath{-}3}$ T). The corresponding NMR spectra for the $S\ensuremath{-}{I}_{N}$ group are investigated by experiment and by simulation. In the strong coupling regime, the maximum number of lines is $(N+1){}^{2}$. In the weak coupling regime ${B}_{1}^{\mathrm{low}}lBl{B}_{2}^{\mathrm{low}}$ at low field, symmetric multiplet structures group around the frequencies $0$, $J$, ($3/2$)$J$, $2J$, ($5/2$)$J$, etc. These spectra determine the structure of the $S\ensuremath{-}{I}_{N}$ group unambiguously and are in dual correspondence to the weakly coupled spectra at high field. High-resolution NMR spectroscopy at ultralow field may open up new ways for chemical analysis by small and mobile instruments with many applications in science and technology.

Developed originally for the Holstein polaron, the Davydov D1 ansatz is an efficient, yet extremely accurate trial state for time-dependent variation of the spin-boson model [N. Wu, L. Duan, X. Li, and Y. Zhao, J. Chem. Phys. 138, 084111 (2013)]. In this work, the Dirac-Frenkel time-dependent variational procedure utilizing the Davydov D1 ansatz is implemented to study entanglement dynamics of two qubits under the influence of two independent baths. The Ohmic spectral density is used without the Born-Markov approximation or the rotating-wave approximation. In the strong coupling regime finite-time disentanglement is always found to exist, while at the intermediate coupling regime, the entanglement dynamics calculated by Davydov D1 ansatz displays oscillatory behavior in addition to entanglement disappearance and revival.

Polariton Lasers do not rely on stimulated emission of photons, a criterion that sets stringent conditions on the threshold current in a conventional laser. Therefore, they have the capability to outperform photon lasers in the weak coupling regime in terms of the threshold power consumption. We present the first successful realization of an electrically pumped polariton laser based on a GaAs/AlAs distributed Bragg reflector cavity. We have furthermore identified the system’s response to an applied magnetic field as a sensitive tool to distinguish a polariton laser from a standard VCSEL device in the weak light-matter coupling regime

Plasmon waveguide resonances (PWRs) have been widely used to enhance the interaction between light and matter. PWRs have been used for chemical and biological sensing, molecular detection, and boosting other optical phenomena, such as Raman scattering and fluorescence. However, the performances of plasmon-waveguide-based structures have been investigated in the angular interrogation mode, and their potential in different spectral regions has hardly been explored. Moreover, the applications of PWRs have been limited to the weak light-matter coupling regime. In this study, we investigate leaky coupled waveguide plasmon resonances (LCWPRs) and explore their potential to enhance light-matter interaction in different spectral regions. In the weak coupling regime, we demonstrate the potential of LCWPRs for sensing in the near-IR region by detecting heavy water (D2O) and ethanol in water. The experimental results show spectral sensitivity of 15.2 nm/% and 1.41 nm/% for ethanol and D2O detection, respectively. Additionally, we show that LCWPRs can be used to achieve vibrational strong coupling (VSC) with organic molecules in the mid-IR region. We numerically show that the coupling between LCWPRs and the C=O stretching vibration of hexanal yields a Rabi splitting of 210 cm-1, putting the system in the VSC regime. We anticipate that LCWPRs will be a promising platform for enhanced spectroscopy, sensing, and strong coupling.

The role of the generalized Pauli constraints (GPCs) in higher spatial dimensions and by incorporating spin degrees of freedom is systematically explored for a system of interacting fermions confined by a harmonic trap. Physical relevance of the GPCs is confirmed by analytical means for the ground state in the regime of weak couplings by finding its vector of natural occupation numbers close to the boundary of the allowed region. Such quasipinning is found to become weaker in the intermediate and strong coupling regime. The study of crossovers between different spatial dimensions by detuning the harmonic trap frequencies suggests that quasipinning is essentially an effect for systems with reduced spatial dimensionality. In addition, we find that quasipinning becomes stronger by increasing the degree of spin-polarization. Consequently, the number of states available around the Fermi level plays a key role for the occurrence of quasipinning. This suggests that quasipinning emerges from the conflict between energy minimization and fermionic exchange symmetry.

We have studied dispersion of surface plasmon polaritons (SPPs) in the Kretcshmann’s geometry (prism/Ag/dye-doped polymer) in weak and strong exciton-plasmon coupling regimes. In reflection, the dispersion curves were in a good agreement with simple model predictions at small concentrations of the dye (R6G) in the polymer (PMMA). At the same time, highly unusual multi-segment ladder-like dispersion curves were observed at large dye concentrations. To describe this behavior, we upgraded the theoretical model taking into account strong exciton-plasmon coupling. The dispersion curves obtained in emission experiments were strongly different from those in reflection and did not seem to be affected by the strong coupling.