arXiv subjects

Ilia Tutunnikov

Publications and source records attributed to Ilia Tutunnikov.

At least 19 recordsLinked to original sources

arXiv2026

Cavity-Mediated Collective Resonant Suppression of Local Molecular Vibrations

Recent advances in polaritonic chemistry suggest that chemical reactions can be controlled via collective vibrational strong coupling (VSC) in a cavity. In this fully analytical work, we demonstrate that the collective vibrations of a molecular ensemble under VSC execute a beating with a period inversely proportional to the collective vacuum Rabi splitting. Significantly, this collective beating is imprinted on the local dynamics and resonantly suppresses individual molecular vibrations when a fraction of molecules are vibrationally excited, as in activated complexes formed in chemical reactions. This emergent beating occurs on significantly longer time scales than the individual molecular vibration or the cavity field oscillation period, peaking at the cavity-molecule resonance, consistent with polaritonic chemistry experiments. The cavity mediates an energy exchange between excited and ground-state molecules, affecting the dynamics of the entire ensemble. These findings suggest that the dynamics in polaritonic chemical reactions may not be in full equilibrium. In the ultra-strong coupling regime, we find that the local vibrations are modified by the cavity even at short time scales. Notably, these dynamical effects also extend to isotropic molecular ensembles in our model. Our analytical model offers insights into how collective VSC can dampen local molecular vibrations at resonance, potentially altering chemical reactivity.

quant-ph↗

arXiv2026

Direct imaging of enantiomer-specific orientation dynamics in unidirectionally rotating chiral molecules

Selectively controlling the dynamics of molecular enantiomers underlies advances across chemistry, biology, and physics, yet direct imaging of enantiomer-specific motion has so far remained elusive. Here, we image ultrafast enantioselective orientation dynamics in isolated chiral molecules. Unidirectional coherent rotation induced by a femtosecond laser-pulse pair generates equal and opposite out-of-plane orientations of the two enantiomers. Applying this scheme to 2-methyloxirane, we follow the rotational wave packets by time-resolved Coulomb explosion imaging with two orthogonally arranged detectors. The measured angular distributions reveal that the unidirectional rotation is identical for both enantiomers, while the out-of-plane orientations are mirror images that persist through both early-time quasi-classical and quantum dynamics regimes, in quantitative agreement with simulations. We demonstrate that full angular distributions provide richer dynamical information, with some qualitatively different distributions yielding similar orientation factors upon integration. Our approach opens a route to real-time observation and control of chiral dynamics in the gas phase.

physics.chem-ph↗

arXiv2026

Noise-enhanced Ballistic Expansion of Polariton Wave-packets in a Multimode Cavity

Advances in optical measurements enable precise tracking of cavity polariton wave-packets across broad spatial and temporal ranges, but how dephasing reshapes their real-space dynamics over multiple time scales remains unclear. Here we show, using a stochastic multimode Tavis-Cummings model, that dephasing noise leads to a robust hierarchy of dynamical regimes comprising Rabi oscillation damping, center-of-mass slowdown, population relaxation, and ballistic-to-diffusive crossover, in the order of increasing time scales. We further predict that dephasing can enhance ballistic spreading and sustain it far beyond the microscopic dephasing time by two orders of magnitude. These predictions agree with recent microscopy measurements and provide experimentally testable guidance for engineering energy transport in polaritonic platforms.

physics.optics↗

arXiv2025

Characterization of Polariton Dynamics in a Multimode Cavity (II): Coherent-Incoherent Transition Driven by Photon Loss

Motivated by the recent advances in optical imaging and tracking of wave-packet propagation in optical cavities, we systematically explore the non-Hermitian polariton dynamics within a decay-tunable multimode cavity model. The complex eigen-spectrum of the model Hamiltonian allows us to predict the incoherent-coherent transition induced by photon losses, which defines an exceptional point at resonance and evolves analytically as the wavevector shifts off-resonantly. The resulting dispersion relation, group velocity, and relaxation rate exhibit striking signatures, such as curve crossing, level repulsion, turnover, bifurcation, and coalescence, as the decay rate crosses the critical transition or the wavevector crosses the resonance. The spectral characterization leads to surprising features in the non-Hermitian wave packet dynamics: (i) maximal population relaxation rate at the critical transition; (ii) reversed propagation in the center-of-mass motion; (iii) ballistic-to-diffusion transition; (iv) contraction in the displacement and width of the polariton wave-packet. These dynamical features have complementary symmetry between the upper-polariton (UP) branch and lower-polariton (LP) branch in the two-dimensional phase diagram spanned by the photon decay rate and wavevector. Thus, the combination of complex spectral characterization and non-Hermitian wave packet propagation establishes the photon decay rate as a powerful control parameter for polariton transport, reveals the underlying symmetry in lossy cavities, and presents a starting point to incorporate other dissipative mechanisms.

quant-ph↗

arXiv2025

Echoes in a parametrically perturbed Kerr-nonlinear oscillator

We study classical and quantum echoes in a Kerr oscillator driven by a frequency-controlling pulsed perturbation. We consider dynamical response to the perturbation for a single coherent state and for Schrödinger cat states constructed as both balanced and imbalanced superpositions of two coherent states. For individual coherent states, we demonstrate that a weak parametric drive yields a long-lived sequence of classical echoes. Cat states are found to exhibit distinct quantum echoes that are sensitive to the initial relative phase and weights of the coherent states in superposition. We examine the effect of dissipation on quantum echoes and quantum revivals of cat states. We demonstrate that, even when dissipation suppresses quantum revivals, quantum echoes can be recovered by properly tuning the timing and strength of the perturbation. These results may be useful for characterizing and mitigating errors of cat qubits.

quant-ph↗

arXiv2024

Dynamical generation and transfer of nonclassical states in strongly interacting light-matter systems in cavities

We propose leveraging strong and ultrastrong light-matter coupling to efficiently generate and exchange nonclassical light and quantum matter states. Two initial conditions are considered: (a) a displaced quadrature-squeezed matter state, and (b) a coherent state in a cavity. In both scenarios, polaritons mediate the dynamical generation and transfer of nonclassical states between light and matter. By monitoring the dynamics of both subsystems, we uncover the emergence of beatings in the collective matter oscillations. The beating period depends on the particle density through the vacuum Rabi splitting and peaks sharply under light-matter resonance conditions. For initial condition (a), nonclassicality is efficiently transferred from matter to photons under strong and ultrastrong coupling. However, for initial condition (b), nonclassical photonic states are generated only in the ultrastrong coupling regime due to the counter-rotating terms, highlighting the advantages of ultrastrong coupling. Furthermore, in the ultrastrong coupling regime, distinctive asymmetries relative to cavity detuning emerge in dynamical observables of both light and matter. The nonclassical photons can be extracted through a semi-transparent cavity mirror, while nonclassical matter states can be detected via time-resolved spectroscopy. This work highlights that hybrid polariton states can be utilized for dynamically generating nonclassical states, with potential applications in quantum state transfer.

quant-ph↗

arXiv2024

Unusual Diffusivity in Strongly Disordered Quantum Lattices: Random Dimer Model

Recent advances in transport properties measurements of disordered materials and lattice simulations, using superconducting qubits, have rekindled interest in Anderson localization, motivating our study of highly disordered quantum lattices. Initially, our statistical analysis of localized eigenstates reveals a distinct transition between weak and strong disorder regimes, suggesting a random distribution of dimers in highly disordered systems. Subsequently, the random dimer model predicts an oscillating diffusivity that decays as $t^{-1/2}$, is inversely proportional to the disorder strength, and maintains a constant frequency with an initial phase shift of $π/4$. The first peak exhibits a universal scaling of $σ^{-1}$ both in peak time and amplitude. Finally, we find that stochastic noise suppresses these oscillations and induces hopping between localized eigenstates, resulting in constant diffusion over long times. Our predictions challenge the conventional understanding of incoherent hopping under strong disorder. This offers new insights to optimize disordered systems for optoelectrical and quantum information technologies.

quant-ph↗

arXiv2023

Enhanced Persistent Orientation of Asymmetric-Top Molecules Induced by Cross-Polarized Terahertz Pulses

We investigate the persistent orientation of asymmetric-top molecules induced by time-delayed THz pulses that are either collinearly or cross polarized. Our theoretical and numerical results demonstrate that the orthogonal configuration outperforms the collinear one, and a significant degree of persistent orientation - approximately 10% at 5 K and nearly 3% at room temperature - may be achieved through parameter optimization. The dependence of the persistent orientation factor on temperature and field parameters is studied in detail. The proposed application of two orthogonally polarized THz pulses is both practical and efficient. Its applicability under standard laboratory conditions lays a solid foundation for future experimental realization of THz-induced persistent molecular orientation.

physics.chem-ph↗

arXiv2023

Coherent spatial control of wave packet dynamics on quantum lattices

Quantum lattices are pivotal in the burgeoning fields of quantum materials and information science. Rapid developments in microscopy and quantum engineering allow for preparing and monitoring wave-packet dynamics on quantum lattices with increasing spatial and temporal resolution. Motivated by these emerging research interests, we present an analytical study of wave packet diffusivity and diffusion length on tight-binding quantum lattices subject to stochastic noise. Our analysis points to the crucial role of spatial coherence and predicts a set of novel phenomena: noise can enhance the transient diffusivity and diffusion length of sufficiently extended initial states; A smooth Gaussian initial state spreads slower than a localized initial state; A standing or traveling initial state with large momentum spreads faster than a localized initial state and exhibits a noise-induced peak in the transient diffusivity; The change in the time-dependent diffusivity and diffusion length relative to a localized initial state follows a universal dependence on the Gaussian width. These theoretical predictions and the underlying mechanism of spatial coherence suggest the possibility of controlling the wave packet dynamics on quantum lattices by spatial manipulations, which will have implications for materials science and quantum technologies.

quant-ph↗

arXiv2022

Ionization-induced Long-lasting Orientation of Symmetric-top Molecules

We theoretically consider the phenomenon of field-free long-lasting orientation of symmetric-top molecules ionized by two-color laser pulses. The anisotropic ionization produces a significant long-lasting orientation of the surviving neutral molecules. The degree of orientation increases with both the pulse intensity and, counterintuitively, with the rotational temperature. The orientation may be enhanced even further by using multiple delayed two-color pulses. The long-lasting orientation may be probed by even harmonic generation or by Coulomb-explosion-based methods. The effect may enable the study of relaxation processes in dense molecular gases, and may be useful for molecular guiding and trapping by inhomogeneous fields.

physics.chem-ph↗

arXiv2022

Echo-enhanced molecular orientation at high temperatures

Ultrashort laser pulses are widely used for transient field-free molecular orientation -- a phenomenon important in chemical reaction dynamics, ultrafast molecular imaging, high harmonics generation, and attosecond science. However, significant molecular orientation usually requires rotationally cold molecules, like in rarified molecular beams, because chaotic thermal motion is detrimental to the orientation process. Here we propose to use the mechanism of the echo phenomenon previously observed in hadron accelerators, free-electron lasers, and laser-excited molecules to overcome the destructive thermal effects and achieve efficient field-free molecular orientation at high temperatures. In our scheme, a linearly polarized short laser pulse transforms a broad thermal distribution in the molecular rotational phase space into many separated narrow filaments due to the nonlinear phase mixing during the post-pulse free evolution. Molecular subgroups belonging to individual filaments have much-reduced dispersion of angular velocities. They are rotationally cold, and a subsequent moderate terahertz (THz) pulse can easily orient them. The overall enhanced orientation of the molecular gas is achieved with some delay, in the course of the echo process combining the contributions of different filaments. Our results demonstrate that the echo-enhanced orientation is an order of magnitude higher than that of the THz pulse alone. The mechanism is robust -- it applies to different types of molecules, and the degree of orientation is relatively insensitive to the temperature. The laser and THz pulses used in the scheme are readily available, allowing quick experimental demonstration and testing in various applications. Breaking the phase space to individual filaments to overcome hindering thermal conditions may find a wide range of applications beyond molecular orientation.

physics.chem-ph↗

arXiv2022

Gradient-based reconstruction of molecular Hamiltonians and density matrices from time-dependent quantum observables

We consider a quantum system with a time-independent Hamiltonian parametrized by a set of unknown parameters $α$. The system is prepared in a general quantum state by an evolution operator that depends on a set of unknown parameters $P$. After the preparation, the system evolves in time, and it is characterized by a time-dependent observable ${\cal O}(t)$. We show that it is possible to obtain closed-form expressions for the gradients of the distance between ${\cal O}(t)$ and a calculated observable with respect to $α$, $P$ and all elements of the system density matrix, whether for pure or mixed states. These gradients can be used in projected gradient descent to infer $α$, $P$ and the relevant density matrix from dynamical observables. We combine this approach with random phase wave function approximation to obtain closed-form expressions for gradients that can be used to infer population distributions from averaged time-dependent observables in problems with a large number of quantum states participating in dynamics. The approach is illustrated by determining the temperature of molecular gas (initially, in thermal equilibrium at room temperature) from the laser-induced time-dependent molecular alignment.

quant-ph↗

arXiv2022

Optimal Selective Orientation of Chiral Molecules Using Femtosecond Laser Pulses

We present a comprehensive study of enantioselective orientation of chiral molecules excited by a pair of delayed cross-polarized femtosecond laser pulses. We show that by optimizing the pulses' parameters, a significant (~ 10%) degree of enantioselective orientation can be achieved at zero and at five kelvin rotational temperatures. This study suggests a set of reasonable experimental conditions for inducing and measuring strong enantioselective orientation. The strong enantioselective orientation and the wide availability of the femtosecond laser systems required for the proposed experiments may open new avenues for discriminating and separating molecular enantiomers.

physics.optics↗

arXiv2021

Rotation of polarization of light propagating through a gas of molecular super-rotors

We present a detailed theoretical and experimental study of the rotation of the plane of polarization of light traveling through a gas of fast-spinning molecules. This effect is similar to the polarization drag phenomenon predicted by Fermi a century ago and it is a mechanical analog of the Faraday effect. In our experiments, molecules were spun up by an optical centrifuge and brought to the super-rotor state that retains its rotation for a relatively long time. Polarizability properties of fast-rotating molecules were analyzed considering the rotational Doppler effect and Coriolis forces. We used molecular dynamics simulations to account for intermolecular collisions. We found, both experimentally and theoretically, a nontrivial nonmonotonic time dependence of the polarization rotation angle. This time dependence reflects transfer of the angular momentum from rotating molecules to the macroscopic gas flow, which may lead to the birth of gas vortices. Moreover, we show that the long-term behavior of the polarization rotation is sensitive to the details of the intermolecular potential. Thus, the polarization drag effect appears as a novel diagnostic tool for the characterization of intermolecular interaction potentials and studies of collisional processes in gases.

physics.optics↗

arXiv2021

Visualizing coherent molecular rotation in a gaseous medium

Inducing and controlling the ultrafast molecular rotational dynamics using shaped laser fields is essential in numerous applications. Several approaches exist that allow following the coherent molecular motion in real-time, including Coulomb explosion-based techniques and recovering molecular orientation from the angular distribution of high harmonics. We theoretically consider a non-intrusive optical scheme for visualizing the rotational dynamics in an anisotropic molecular gas. The proposed method allows determining the instantaneous orientation of the principal optical axes of the gas. The method is based on probing the sample using ultra-short circularly polarized laser pulses and recording the transmission image through a vortex wave plate. We consider two example excitations: molecular alignment induced by an intense linearly polarized laser pulse and unidirectional molecular rotation induced by a polarization-shaped pulse. The proposed optical method is promising for visualizing the dynamics of complex symmetric- and asymmetric-top molecules.

physics.optics↗

arXiv2021

Three Dimensional Orientation of Complex Molecules Excited by Two-Color Femtosecond Pulses

We study the excitation of asymmetric-top (including chiral) molecules by two-color femtosecond laser pulses. In the cases of non-chiral asymmetric-top molecules excited by an orthogonally polarized two-color pulse, we demonstrate, classically and quantum mechanically, three-dimensional orientation. For chiral molecules, we show that the orientation induced by a cross-polarized two-color pulse is enantioselective along the laser propagation direction, namely, the two enantiomers are oriented in opposite directions. On the short time scale, the classical and quantum simulations give results that are in excellent agreement, whereas on the longer time scale, the enantioselective orientation exhibits quantum beats. These observations are qualitatively explained by analyzing the interaction potential between the two-color pulse and molecular (hyper-)polarizability. The prospects for utilizing the long-lasting orientation for measuring and using the enantioselective orientation for separating the individual enantiomers are discussed.

physics.optics↗

arXiv2021

Long-Lasting Orientation of Symmetric-top Molecules Excited by Two-Color Femtosecond Pulses

Impulsive orientation of symmetric-top molecules excited by two-color femtosecond pulses is considered. In addition to the well-known transient orientation appearing immediately after the pulse and then reemerging periodically due to quantum revivals, we report the phenomenon of field-free long-lasting orientation. Long-lasting means that the time averaged orientation remains non-zero until destroyed by other physical effects, e.g. intermolecular collisions. The effect is caused by the combined action of the field-polarizability and field-hyperpolarizability interactions. The dependence of degree of long-lasting orientation on temperature and pulse's parameters is considered. The effect can be measured by means of second (or higher-order) harmonic generation, and may be used to control the deflection of molecules traveling through inhomogeneous electrostatic fields.

physics.optics↗

arXiv2020

Enantioselective Orientation of Chiral Molecules Induced by Terahertz Pulses with Twisted Polarization

Chirality and chiral molecules are key elements in modern chemical and biochemical industries. Individual addressing, and the eventual separation of chiral enantiomers has been and still is an important elusive task in molecular physics and chemistry, and a variety of methods has been introduced over the years to achieve this goal. Here, we theoretically demonstrate that a pair of cross-polarized THz pulses interacting with chiral molecules through their permanent dipole moments induces an enantioselective orientation of these molecules. This orientation persists for a long time, exceeding the duration of the THz pulses by several orders of magnitude, and its dependency on temperature and pulses' parameters is investigated. The persistent orientation may enhance the deflection of the molecules in inhomogeneous electromagnetic fields, potentially leading to viable separation techniques.

physics.optics↗