arXiv subjects

Misha Ivanov

Publications and source records attributed to Misha Ivanov.

At least 19 recordsLinked to original sources

arXiv2026

Quantum Optics of harmonic generation in the strongly driven Jaynes-Cummings-type system

We adapt the Jaynes-Cummings model to study the interface of cavity quantum electrodynamics with strong field and attosecond physics. We show how multi-photon resonances in the Jaynes- Cummings system driven by a strong low-frequency classical light field lead to the generation of highly non-classical, quantum-correlated harmonics of the classical driver. Our treatment assumes no approximations, apart from the typical Jaynes-Cummings model assumption of only a few discrete quantum modes of light. The paper is dedicated to Joseph Henry Eberly, whose remarkable research has left indelible mark on both strong field physics and quantum optics.

quant-ph↗

arXiv2026

Extreme Ultrafast Dynamics of the Refractive Index in Transparent Conductive Oxides: Theory and Experiment

Recent experiments in transparent conductive oxides (TCOs) have revealed light-induced order-unity variations in the refractive index occurring at extreme time scales, as short as a few-femtoseconds. These experimental observations remain unexplained, especially the ultrafast 10-20 femtoseconds relaxation of the index change, that cannot be explained by known phonon-mediated relaxation processes. Here, we present a simplified model followed by comprehensive simulations describing the phenomena, relying on the microscopic dynamics of electrons in TCOs under powerful ultrafast laser pulses. With this physical model, we predict and experimentally observe the unexplored regime of intraband modulation of electrons in the conduction band, leading to ultrafast oscillations of the refractive index. The observation of the oscillations validates the theory as a predictive tool, utilizing it to design experiments targeting novel effects that hinge on extreme alterations of optical properties of materials, such as photonic time-crystals and a plethora of novel extreme ultrafast phenomena.

physics.optics↗

arXiv2026

Valley polarization driven by two-color circular fields: a rotating frame and strong-field perspective

Valley polarization in hexagonal materials driven by the form of the lightwave and its orientation relative to the lattice, rather than solely by the helicity of the driver, has recently been demonstrated both theoretically and experimentally. This has extended valley control to the non-resonant, sub-cycle regime and to inversion-symmetric materials. One interpretation of this field-orientation-dependent valley polarization is that the laser-dressed, cycle-averaged band structure obtained from a Floquet-type approach is modified so as to lift the degeneracy between the valleys. Here, we derive a complementary explanation based on strong-field tunneling dynamics. We show that the effective valley gap at the dominant injection times depends on the orientation of the field relative to the lattice through the trigonal-warping term of the low-energy dispersion. We derive general expressions for co- and counter-rotating $\omega+N\omega$ fields and show that the leading orientation-dependent contribution survives the cycle average only for field configurations compatible with the threefold lattice symmetry, most notably counter-rotating $\omega+2\omega$ and co-rotating $\omega+4\omega$ fields. As a complementary weak-field result, we show that, for counter-rotating bicircular fields, the one-photon valley selection rules can be represented as valley-dependent energy detunings in a rotating frame where both colors acquire the same frequency.

physics.optics↗

arXiv2026

Coherent control of chirality in Weyl semimetals

Weyl fermions in inversion-symmetric Weyl semimetals occur in pairs of opposite chirality, leading to symmetric optical responses under circularly-polarised light and a vanishing net photocurrent. Here, we show that tailored two-colour light fields break this symmetry and enable selective excitation of individual Weyl nodes. The interference between a circularly-polarised $\omega$ field and a phase-locked linearly-polarised $2\omega$ field generates a chirality-dependent redistribution of carriers in momentum space, resulting in a nonzero controllable photocurrent. We demonstrate that both the magnitude and sign of the photocurrent can be tuned via the relative phase and field strength of the two colours, and identify an optimal regime in which chiral selectivity is maximised. Our results establish a general route to optically-controlled chiral charge dynamics in Weyl semimetals using polarisation-structured light.

cond-mat.mes-hall↗

arXiv2026

Sub-cycle field-driven dynamical Berry phase in solids

In quantum mechanics, a wavepacket acquires a geometric phase, known as the Berry phase, as it evolves along a closed trajectory in parameter space. In condensed matter systems, the Berry phase underlies a broad range of phenomena, including the anomalous Hall effect, orbital magnetism, and electric polarization. However, in centrosymmetric materials possessing time-reversal (TR) symmetry, its manifestation is suppressed and effectively vanishes. When a system is driven by a strong terahertz (THz) field, it can be coherently driven far from equilibrium, transiently reshaping its symmetry on sub-picosecond timescales. This capability opens new avenues for quantum control with potential applications in information processing and sensing. Here, we experimentally demonstrate that a strong THz field can transiently break inversion symmetry in MgO, inducing a dynamical complex Berry phase, thereby manipulating the topological properties of the material. Applying high-harmonic generation (HHG) spectroscopy, we directly resolve the Berry phase, accessing both its real and imaginary components. The first is associated with coherent intraband dynamics while the second with quantum tunneling through a potential barrier. This observation enables the reconstruction of the time-dependent evolution of the Berry phase within the cycle of the THz field. The coherent manipulation of solids with strong fields, combined with attosecond-resolved HHG spectroscopy, represents a fundamental step toward unveiling and controlling geometric quantum phenomena in condensed matter systems.

cond-mat.mtrl-sci↗

arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗

arXiv2026

Attosecond quantum spectroscopy with entangled photon pairs

Bright squeezed light from parametric down-conversion in the infrared (IR) frequency range has triggered the emergence of attosecond quantum optics -- a new research field at the interface of quantum optics, strong-field physics, and attosecond technology. Two challenges arise at this interface: transferring quantum features of the IR light sources to the ultraviolet (UV) and extreme ultraviolet (XUV) frequency range via strong-field nonlinearities, and exploiting quantum optical properties of the nonlinear optical response as a new probe in ultrafast dynamics. Here, we address both by driving high-harmonic generation (HHG) in solids with entangled photon pairs either in degenerate or non-degenerate frequency modes. In the degenerate mode, single-shot measurements of harmonics up to the 10th order reveal strong photon bunching whose $g^{(2)}$ first grows and then decreases with the harmonic order. We show that this behavior tracks different microscopic mechanisms responsible for harmonic emission, demonstrating the potential of attosecond quantum optical spectroscopy. In the non-degenerate case, the harmonics retain quantum-induced correlations, verified by wavelength-resolved second-order cross-correlation maps. Our findings demonstrate transfer of quantum photon correlations into the XUV domain and open a pathway toward quantum-enhanced attosecond spectroscopy and control of ultrafast dynamics in solids.

physics.optics↗

arXiv2026

A finite-difference model for intense light interactions with dielectrics in the ultrafast ionization regime

We present a computationally efficient model that describes the interaction of intense, ultrashort infrared laser pulses with transparent materials in the strong ionization regime. The model is augmented with a detailed self-consistent description of the local response due to ionization and collisional plasma dynamics. It incorporates the direct solution of Maxwell's equations without approximations and rigorous boundary conditions for the input pulse, allowing us to study the ultrafast formation of over-critical nanoscaled plasmas in dielectric materials under the influence of intense tightly focused laser pulses. We perform a scan of the parameter space, find unexpected optima regimes for different experientially relevant parameters, and explain these maxima based on spatiotemporal dynamics.

physics.plasm-ph↗

arXiv2026

Geometric mechanisms enabling spin- and enantio-sensitive observables in one photon ionization of chiral molecules

We examine spin-resolved photoionization of randomly oriented chiral molecules via circularly polarized light, and revisit earlier predictions of Cherepkov (J. Phys. B: Atom. Mol. Phys. 16, 1543, 1983). We will show that the dynamical origin of spin- and enantio-sensitive observables arise from two intrinsic mechanisms that are quantified by two pseudovectors stemming from the geometric properties of the photoionization dipoles in spin space and in real space, and an extrinsic mechanism which is a directional bias introduced by the well-defined direction of light polarization. These mechanisms arise solely from electric dipole interactions. Consequently, this means that the ten independent parameters that was earlier predicted by Cherepkov to fully describe spin-resolved photoionization of chiral molecules can be reduced as moments of these three pseudovectors. We also find that the molecular pseudoscalars describing the spin- and enantio-sensitive components of the yield can be described by the flux of these pseudovectors through the energy shell, which changes sign upon switching enantiomers. Our results provide compact expressions for these observables which provide an intuitive picture on what determines the strength of these spin- and enantio-sensitive observables. The approach can be readily generalized to photoexcitation, multiphoton processes, and arbitrary field polarizations. Regardless of the specific driving conditions, the resulting spin- and enantio-sensitive observables are still controlled by the same three pseudovectors, underscoring their universal role as the primary generators of chirality-induced spin asymmetries, emphasizing their fundamental geometric origin and the universality of the mechanism identified here.

physics.atom-ph↗

arXiv2025

Attosecond-resolved quantum fluctuations of light and matter

Until recently, attosecond optical spectroscopy and quantum optics evolved along non-overlapping directions. In attosecond science, attosecond pulses have been regarded as classical waves, applied to probe electron dynamics on their natural time scale. Here, we transfer fundamental concepts of quantum optics into attosecond physics, enabling control of both the properties of the XUV attosecond pulses and the quantum fluctuations of matter on attosecond time scales. By combining bright squeezed vacuum (BSV) with a strong laser field to drive high-harmonic generation, we transfer the quantum properties of the BSV onto the resulting XUV attosecond pulses. Applying advanced attosecond interferometry, we reconstruct the quantum state of the XUV high harmonics and their associated attosecond pulses with attosecond precision. Finally, we resolve the squeezing of the electron's wavepacket during one of the most fundamental strong-field phenomena - field induced tunneling. The ability to measure and control quantum correlations in both electrons and XUV attosecond pulses establishes a foundation for attosecond quantum electrodynamics, manipulating the quantum state of electrons and photons with sub-cycle precision.

physics.optics↗

arXiv2025

Spontaneous symmetry breaking in nonlinear superradiance

Creation and manipulation of non-classical states of light is rapidly becoming the focus of modern attosecond science. Here, we demonstrate numerically how interaction with such states can trigger the emergence of a many-body system with spontaneously broken symmetry by considering a modification of the well-known problem of superradiance encountered already by Dicke. Similarly to him, we investigate photon emission by ensembles of indistinguishable atoms. In contrast to him, however, we leverage symmetry-based selection rules to suppress emission of single photons by single atoms. A steady state is therefore only reached following a spontaneous transition into a collective symmetry-broken state of atoms and photonic modes. This transition permanently locks the atomic dipoles to the quantum field experienced by the system at a particular instant, transforming the entire setup into a potent quantum sensor reproducing the phase of the recorded quantum fluctuation.

quant-ph↗

arXiv2025

Semiconductor Wannier equations: a real-time, real-space approach to the nonlinear optical response in crystals (ATATA)

We develop the semiconductor Wannier equations (SWEs), a real-time, real-space formulation of ultrafast light-matter dynamics in crystals, by deriving the equations of motion for the electronic reduced density matrix in a localized Wannier basis. Working in real space removes the structure-gauge ambiguities that hinder reciprocal-space semiconductor Bloch equations. Electron--electron interactions are included at the time-dependent Hartree plus static screened-exchange (TD-HSEX) level. Decoherence is modeled with three complementary channels: pure dephasing, population relaxation, and distance-dependent real-space dephasing; providing physically grounded damping for strong-field phenomena such as high-harmonic generation. Conceptually, the SWEs bridge real-space semiclassical intuition with many-body solid-state optics, offering a numerically robust and gauge-clean alternative to reciprocal-space approaches for nonlinear optical response and attosecond spectroscopy in solids.

physics.optics↗

arXiv2025

Spin-current correlations in photoionization of chiral molecules

Chirality-induced spin selectivity (CISS) refers to phenomena where molecular chirality governs spin polarization. While symmetry simply requires chiral molecules to support spin-vector correlations, we show that CISS is fundamentally a conditioned measurement of these correlations. We illustrate this principle for spin-resolved one-photon ionization of a randomly oriented ensemble of chiral molecules. We introduce and quantify the phenomenon of enantio-sensitive locking of the photoelectron current to its spin, thereby providing a complete description of spin-conditioned photoelectron currents in one-photon ionization.

quant-ph↗

arXiv2025

Enantiosensitive molecular compass

Chirality describes the asymmetry between an object and its mirror image and underlies diverse functionalities across molecular, mesoscopic and bulk matter. A particularly intriguing example is chirality-induced spin selectivity (CISS), where chiral structures generate enantio-sensitive spin polarization. Despite extensive research, its microscopic origin and unexpectedly large magnitude remain unresolved. Here, we isolate the intrinsic coupling between chirality and spin by considering spin-resolved photoionization of randomly oriented chiral molecules under isotropic illumination. We show that electric-dipole photoionization in the presence of spin-orbit coupling generates intrinsic correlations between molecular orientation and photoelectron spin that survive complete isotropic averaging. We identify these spin-orientation correlations as the microscopic origin of CISS in photoionization and reveal their complementary manifestation: selecting the photoelectron spin orients the residual molecular ensemble, realizing spin-orientation locking, whereas selecting molecular orientation produces CISS. Both effects are governed by the same correlation strength, set by the magnitude of a molecular-frame photoionization Bloch vector that defines an enantio-sensitive molecular compass. An analogous compass emerges in photoexcitation. Our results establish spin - orientation correlations as a fundamental ingredient of chiral spin photodynamics and provide a microscopic framework for understanding and exploiting spin selectivity in chiral matter.

cond-mat.mes-hall↗

arXiv2025

Enantiosensitive exceptional points in open chiral systems

Exceptional points (EPs) are remarkable spectral degeneracies in a non-Hermitian system's parameter space, where both eigenvalues and eigenstates coalesce. Here, we show that in non-Hermitian molecular chiral systems the position of EPs in the parameter space is enantiomer-specific. First, we show that encircling the EP of one enantiomer drives robust topological population transfer in the chiral molecule while its mirror twin remains unaffected, offering a new route for selective chiral control. Second, we reveal how resonant excitation of EPs in chiral molecules can amplify weak chiral effects, offering an alternative approach to the enhancement of chiral interactions. Third, we demonstrate that a twisted chiral fiber immersed in a liquid solution of chiral molecules exhibits topologically different behavior depending on the solution's enantiomeric excess, offering a new approach to the detection of molecular chirality. Our results combine high enantiosensitivity with topological robustness in chiral discrimination and control, paving the way for new approaches in the exploration of non-Hermitian and chiral phenomena.

quant-ph↗

arXiv2024

Ultrafast valleytronic logic operations

Information processing currently reaches speeds as high as 800 GHz. However, the underlying transistor technology is quickly approaching its fundamental limits and further progress requires a disruptive approach. One such path is to manipulate quantum properties of solids, such as the valley degree of freedom, with ultrashort controlled lightwaves. Here we employ a sequence of few-optical-cycle visible pulses controlled with attosecond precision to excite and switch the valley pseudospin in a 2D semiconductor. We show that a pair of pulses separated in time with linear orthogonal polarizations can induce a valley-selective population. Additionally, exploiting a four-pump excitation protocol, we perform logic operations such as valley de-excitation and re-excitation at room temperature at rates as high as ~10 THz.

cond-mat.mes-hall↗

arXiv2024

Towards multi-petahertz all-optical electric field sampling

We present an all-optical concept for measuring the electric field of light spanning from infrared to extreme ultraviolet with multi-petahertz detection bandwidth. Our approach employs a heterodyne detection of light produced by a highly nonlinear light-matter interaction gate. We establish a numerical model of a complex spectral response for unambiguous electric field extraction and benchmark it against the experiment. We show that the concept can be applied for measuring wavelengths down to about 60 nm with a high sensitivity and dynamic range of about 40 decibels. This opens up unprecedented perspectives for spatio-temporal electric field-resolved experiments and control of broadband dynamics of matter.

physics.optics↗

arXiv2024

Revealing the Berry phase under the tunneling barrier

In quantum mechanics, a quantum wavepacket may acquire a geometrical phase as it evolves along a cyclic trajectory in parameter space. In condensed matter systems, the Berry phase plays a crucial role in fundamental phenomena such as the Hall effect, orbital magnetism, and polarization. Resolving the quantum nature of these processes commonly requires sensitive quantum techniques, as tunneling, being the dominant mechanism in STM microscopy and tunneling transport devices. In this study, we integrate these two phenomena - geometrical phases and tunneling - and observe a complex-valued Berry phase via strong field light matter interactions in condensed matter systems. By manipulating the tunneling barrier, with attoseconds precision, we measure the imaginary Berry phase accumulated as the electron tunnels during a fraction of the optical cycle. Our work opens new theoretical and experimental directions in geometrical phases physics and their realization in condensed matter systems, expanding solid state strong field light metrology to study topological quantum phenomena.

cond-mat.mes-hall↗