arXiv subjects

Jino George

Publications and source records attributed to Jino George.

9 recordsLinked to original sources

arXiv2026

Structured input-output analysis of oblique turbulent bands in Waleffe flow

This work employs structured input-output analysis (SIOA) to study Waleffe flow. The SIOA framework employs structured uncertainty to include the componentwise structure of nonlinearity in Navier-Stokes equations, and SIOA quantifies the flow response using structured singular values. The structured input-output analysis identifies the wavelength and inclination angle of oblique turbulent bands observed in large-domain direct numerical simulations. The structured input-output response scales over Reynolds number as $\sim Re^{1.7}$.

physics.flu-dyn↗

arXiv2025

Identifying Exceptional Points in Two-Dimensional Excitons Coupled to an Open Optical Cavity

Strong coupling in the conventional sense requires that the Rabi cycling process between two interacting states is faster than other dissipation rates. Some recent experimental findings show intriguing properties that were attributed to polaritonic states (e.g., plexcitons) even though the above criterion is not satisfied. Here, we theoretically predict and provide experimental evidence of polariton-like behavior in a system that does not show Rabi splitting. The photoluminescence of an exciton-cavity system consisting of a two-dimensional exciton monolayer (tungsten disulfide, WS2) coupled to a planar, open, one-mirror optical cavity configuration is studied. We experimentally observed a transition from the weak coupling regime crossing an exceptional point to form polariton-like states by varying the coupling strength and the cavity loss. Our observations are fully in agreement with a theoretical quasi-normal mode analysis, which predicts this transition and confirms the presence of exceptional points in the system. These results provide evidence that polaritonic effects can be experimentally observed even when the conventional strong coupling condition is not satisfied.

cond-mat.mtrl-sci↗

arXiv2025

The Role of Dark States on Azopyrrole Photoisomerization Reaction by Varying the Coupling Strength of Light-Matter Interaction

Strong light-matter interactions are gaining importance in controlling the photoswitching behavior of molecules exhibiting bistability. Here, we used the strategy of electronic strong coupling of both the E and Z-isomers of azopyrrole photoswitches to a single cavity mode, thereby tuning the conditions from strong to weak coupling in an on-the-go photoisomerization process. This allows in situ monitoring of apparent rates of forward and backward reactions. Very interestingly, the kinetics follow a non-linear trend with a sharp switch in the kinetic slope at the intermediate coupling regime. At this condition, pumping at the upper polaritonic state and the uncoupled population shows an acceleration of the photoisomerization process mediated by the dark state manifold. On the other hand, an opposite effect is observed while exciting the lower polaritonic state. Performing the same experiment in the ultra-strong coupling regime shows no dynamic change over time but further emphasizes the outstanding role of the lower polaritonic states. Our experimental and theoretical findings underline the importance of collective strong coupling in tailoring energy transfer to control photoisomerization dynamically.

physics.chem-ph↗

arXiv2024

Polariton-Based Room Temperature Quantum Phototransistors

Strong light-matter coupling is a quantum process in which light and matter are coupled together, generating hybridized states. This is similar to the notion of molecular hybridization, but one of the components is light. Here, we utilized the idea and prepared quantum phototransistors using donor-acceptor combinations that can transfer energy via Rabi oscillations. As a prototype experiment, we used a cyanine J-aggregate (TDBC; donor) and MoS2 monolayer (acceptor) in a field effect transistor cavity and studied the photoresponsivity. The energy migrates through the newly formed polaritonic ladder, and the relative efficiency of the device is nearly seven-fold at the ON resonance. Further, the photon mixing fraction is calculated for each independent device and correlated with energy transfer efficiency. In the strongly coupled system, newly formed polaritonic states reshuffle the probability function. A theoretical model based on the time dependent Schrödinger equation is also used to interpret the results. Here, the entangled light-matter states act as a strong channel for funnelling the energy to the MoS2 monolayer, thereby boosting its ability to show the highest photoresponsivity at ON-resonance. These experimental findings and the proposed model suggest novel applications of strong light-matter coupling in quantum materials.

physics.app-ph↗

arXiv2024

Vibrational Strong Coupling of Ro-Vibrational States of Gaseous N2O Molecules

This letter demonstrates the formation of vibro-polaritonic states by strong coupling gaseous nitrous oxide molecules at room temperature. The ro-vibrational features of the molecule is utilized to understand the nature of the strong light-matter interaction in the gas phase. Mixing of the P and R-branch population gives three polaritonic branches, and the dispersion experiments are well supported by three coupled oscillator model. The best mixing of the ro-vibrational population occurs for the middle vibro-polaritonic state, which is formed at the place of the Q-branch (which is otherwise not allowed in the uncoupled system). Further, the Boltzmann distribution is also altered in the strong coupled system. High-resolution spectroscopic studies suggest the presence of a large uncoupled population along with the newly formed vibro-polaritonic states. The gas phase vibrational strong coupling on small molecules proposed here is one step closer to understanding the rate modification in polaritonic chemistry experiments.

physics.chem-ph↗

arXiv2023

Understanding the Nature of Vibro-Polaritonic States in Water and Heavy Water

One of the most popular subjects now being researched in molecular science is strong light-matter coupling. The introduction of vibrational strong coupling and the formation vibro-polaritonic states tend to modify chemical reactivity, energy transfer, and many other physical properties of the coupled system. This is achieved without external stimuli and is very sensitive to the vibrational envelope of the molecular transition. Water is an excellent vibrational oscillator, which is being used for similar experiments. However, the inhomogeneously broad OH/OD stretching vibrational band make it complicated to characterize the vibro-polaritonic states spectroscopically. In this paper, we performed vibrational strong coupling and mapped the evolution of vibro-polaritonic branches from low to high concentration of H2O and measured the on-set of strong coupling. The refractive index dispersion is correlated with the cavity tuning experiments. These results are further compared with transfer matrix simulations. Simulated data deviate as noted in the dispersion spectra as the system enters into ultra-strong coupling condition. A simple oscillator strength correction is made to include the self-dipolar interaction. Hopfield coefficients are also calculated, showing that even at 400 cm-1 detuning, the vibro-polaritonic states still possess light and matter components. Here, we systematically varied the concentration of H2O and mapped the weak, intermediate, and strong coupling regimes to understand the role of inhomogeneously broad OH/OD stretching vibrational band. Our finding may help to better understand the role of H2O/D2O strong coupling in the recent polaritonic chemistry experiments.

physics.chem-ph↗

arXiv2023

Interaction of Confined Light with Optically Structured Thin Film Organic Semiconductor Devices

The pioneering experiments of Karl H. Drexhage explained the classical interaction of light with matter and the modification of the decay rates of an emitter.1 Here, we tried to mimic these experiments in a slightly different configuration and measured the electron mobility of a thin film semiconductor from weak to strong coupling regime. Perylene diimide (organic semiconductor dye) molecules are deposited on a MOSFET device. The refractive index mismatch between the silicon/silicon dioxide layer and the dye molecules forms an interference pattern. The frequency of the interference lines is tuned by changing the thickness of the organic semiconductor. Interestingly, we observed an increase in the electron mobility of the active layer once the system slowly entered into strong coupling condition in a λ cavity. Whereas resonance tuning of a λ/2 cavity does not affect the electron transport, suggesting the system is still in the weak coupling regime. These results are further correlated by optical measurements and transfer matrix simulations. The increase in electron mobility is not large due to high dissipation or low-quality factors of the cavity modes. However, the mirrorless configuration presented here may offer a simpler way of studying the properties of the polaritonic states.

cond-mat.mtrl-sci↗

arXiv2016

Multiple Rabi Splittings under Ultra-Strong Vibrational Coupling

From the high vibrational dipolar strength offered by molecular liquids, we demonstrate that a molecular vibration can be ultra-strongly coupled to multiple IR cavity modes, with Rabi splittings reaching $24\%$ of the vibration frequencies. As a proof of the ultra-strong coupling regime, our experimental data unambiguously reveal the contributions to the polaritonic dynamics coming from the anti-resonant terms in the interaction energy and from the dipolar self-energy of the molecular vibrations themselves. In particular, we measure the opening of a genuine vibrational polaritonic bandgap of ca. $60$ meV. We also demonstrate that the multimode splitting effect defines a whole vibrational ladder of heavy polaritonic states perfectly resolved. These findings reveal the broad possibilities in the vibrational ultra-strong coupling regime which impact both the optical and the molecular properties of such coupled systems, in particular in the context of mode-selective chemistry.

quant-ph↗

arXiv2015

Coherent coupling of molecular resonators with a micro-cavity mode

The optical hybridization of the electronic states in strongly coupled molecule-cavity systems have revealed unique properties such as lasing, room temperature polariton condensation, and the modification of excited electronic landscapes involved in molecular isomerization. Here we show that molecular vibrational modes of the electronic ground state can also be coherently coupled with a micro-cavity mode at room temperature, given the low vibrational thermal occupation factors associated with molecular vibrations, and the collective coupling of a large ensemble of molecules immersed within the cavity mode volume. This enables the enhancement of the collective Rabi-exchange rate with respect to the single oscillator coupling strength. The possibility of inducing large shifts in the vibrational frequency of selected molecular bonds should have immediate consequences for chemistry.

quant-ph↗