arXiv subjects

Liang-You Peng

Publications and source records attributed to Liang-You Peng.

At least 19 recordsLinked to original sources

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

PRBench: End-to-end Paper Reproduction in Physics Research

AI agents powered by large language models exhibit strong reasoning and problem-solving capabilities, enabling them to assist scientific research tasks such as formula derivation and code generation. However, whether these agents can reliably perform end-to-end reproduction from real scientific papers remains an open question. We introduce PRBench, a benchmark of 30 expert-curated tasks spanning 11 subfields of physics. Each task requires an agent to comprehend the methodology of a published paper, implement the corresponding algorithms from scratch, and produce quantitative results matching the original publication. Agents are provided only with the task instruction and paper content, and operate in a sandboxed execution environment. All tasks are contributed by domain experts from over 20 research groups at the School of Physics, Peking University, each grounded in a real published paper and validated through end-to-end reproduction with verified ground-truth results and detailed scoring rubrics. Using an agentified assessment pipeline, we evaluate a set of coding agents on PRBench and analyze their capabilities across key dimensions of scientific reasoning and execution. The best-performing agent, OpenAI Codex powered by GPT-5.3-Codex, achieves a mean overall score of 34%. All agents exhibit a zero end-to-end callback success rate, with particularly poor performance in data accuracy and code correctness. We further identify systematic failure modes, including errors in formula implementation, inability to debug numerical simulations, and fabrication of output data. Overall, PRBench provides a rigorous benchmark for evaluating progress toward autonomous scientific research.

cs.CL↗

arXiv2026

Observation of Strong Electron Correlation in Planetary Atomic Structure

Unravelling two-electron correlation is a long-standing challenge at the heart of few-body quantum physics, underlying correlated phenomena across atomic, molecular and condensed-matter science. In prototypical three-body Coulomb systems, such strong correlation in doubly excited states (DESs) of planetary atomic systems leaves distinct signatures in nonsequential above-threshold double ionization (NS-ATDI) driven by coherent laser fields, yet such targeted study has long remained elusive. Here we present kinematically complete measurements of multi-photon double ionization in cold strontium atoms. Our results reveal a dominant NS-ATDI channel exhibiting well-defined band structures that encode pronounced energy and angular correlations between the two emitted electrons. Autoionization spectra confirm the presence of DESs as transition states that effectively promote the NS-ATDI process. These observations provide direct evidence that both electrons are synchronously excited and ionized via resonant high-lying DES transitions, meaning the structure-linked two-electron correlation of DES is preserved and propagated in the laser-driven time-dependent three-body system. Our work transcends the traditional paradigm of multi-photon double ionization, and fundamentally reshapes the core understanding of intrinsic electron correlation governing many-body systems in nature.

physics.atom-ph↗

arXiv2025

Stable time rondeau crystals in dissipative many-body systems

Driven systems offer the potential to realize a wide range of non-equilibrium phenomena that are inaccessible in static systems, such as the discrete time crystals. Time rondeau crystals with a partial temporal order have been proposed as a distinctive prethermal phase of matter in systems driven by structured random protocols. Yet, heating is inevitable in closed systems and time rondeau crystals eventually melt. We introduce dissipation to counteract heating and demonstrate stable time rondeau crystals, which persist indefinitely, in a many-body interacting system. A key ingredient is synchronization in the non-interacting limit, which allows for stable time rondeau order without generating excessive heating. The presence of many-body interaction competes with synchronization and a de-synchronization phase transition occurs at a finite interaction strength. This transition is well captured via a linear stability analysis of the underlying stochastic processes.

cond-mat.stat-mech↗

arXiv2024

Laser-assisted radiative recombination beyond the dipole approximation

A comprehensive theoretical approach to describe the electron-ion radiative recombination in the presence of intense, short laser pulses, which accounts for nondipole corrections is presented. It is based on the relativistic Coulomb-Volkov solution describing an electron in a combined Coulomb potential and a laser field, which is systematically expanded in powers of $1/c$. Thus, it allows us to trace the origin of nondipole effects observed in the spectrum of emitted radiation. Hence, as we demonstrate for high-frequency pulses assisting the process, a significant extension of the cutoff and asymmetry in angular distributions of the emitted radiation can be attributed to the electron recoil off the laser pulse. In addition, we investigate a possibility of enhancing the efficiency of the generated high-energy radiation by chirping the pulse.

quant-ph↗

arXiv2024

Anomalous photo-induced band renormalization in correlated materials: Case study of Ta$_2$NiSe$_5$

We investigate the anomalous photo-induced band renormalization in correlated materials, exemplified by the case of Ta$_2$NiSe$_5$. The manifestation of this anomaly is characterized by the alternating direction of band shift in response to changes in the laser parameters or electron momentum. We attribute the phenomena to the band inversion of the material and the selective excitation of a high-lying flat band, leading to the competition between the Hartree shift and the order collapse. These findings are based on {\it ab initio} determined effective model for Ta$_2$NiSe$_5$, in which we incorporate high-lying states and the time-dependent GW simulation to follow the non-equilibrium dynamics induced by the laser. Our findings reveal the sensitivity of the non-equilibrium electronic dynamics to the band structure and laser protocols, providing valuable guidance for the selection of suitable materials and lasers in the engineering of band structures.

cond-mat.str-el↗

arXiv2022

Laser-induced electron Fresnel diffraction in the tunneling and over-barrier ionization

The photoelectron momentum distribution in the strong-field ionization has a variety of structures that reveal the complicated dynamics of this process. Recently, we identified a low-energy interference structure in the case of a super-intense extreme ultraviolet (XUV) laser pulse and attributed it to the laser-induced electron Fresnel diffraction. This structure is determined by the laser-induced electron displacement [Geng L et al. 2021 Phys. Rev. A 104(2) L021102]. In the present work, we find that the Fresnel diffraction picture is also present in the tunneling and over-barrier regime of ionization by short pulses. However, the electron displacement is now induced by the electric field component of the laser pulse, instead of by the magnetic field component in the case of the superintense XUV pulse. After corresponding modifications to our quantum and semiclassical models, we find the same physical mechanism of the Fresnel diffraction governs the low-energy interference structures along the laser polarization. The results predicted by the two models agree well with the accurate results from the numerical solution to the time-dependent Schrodinger equation.

physics.atom-ph↗

arXiv2022

Laser-induced electron Fresnel diffraction by XUV pulses at extreme intensity

Ionization of atoms and molecules in laser fields can lead to various interesting interference structures in the photoelectron spectrum. For the case of a super-intense extreme ultraviolet laser pulse, we identify a novel petal-like interference structure in the electron momentum distribution along the direction of the laser field propagation. We show that this structure is quite general and can be attributed to the Fresnel diffraction of the electronic wavepacket by the nucleus. Our results are demonstrated by numerically solving the time-dependent Schrodinger equation of the atomic hydrogen beyond the dipole approximation. By building an analytical model, we find that the electron displacement determines the aforementioned interference pattern. In addition, we establish the physical picture of laser-induced electron Fresnel diffraction which is reinforced by both quantum and semiclassical models.

physics.atom-ph↗

arXiv2018

Michelson Interferometry of High-order Harmonic Generation in Solids

For the high-order harmonic generation in solids, we find a distinct and clean interference pattern in the high-energy end of the spectrum which can be interpreted as a Michelson interferometer of the Bloch electron. Our results are achieved by a numerical solution to the time-dependent Schrödinger equation of the quasi-electron in solids and can be explained by an analytical model based on the principle of the Michelson interferometry. The present study deepens our understanding of the HHG mechanism in crystalline materials and may find potential applications in imaging of the dispersion relation or topological structure of the energy bands in solids.

physics.atom-ph↗

arXiv2018

Photon-momentum transfer in diatomic molecules: an ab initio study

For a molecule, the two-center interference and the molecular scattering phase of the electron are important for almost all the processes that may occur in a laser field. In this study, we investigate their effects in the transfer of linear photon momentum to the ionized electron by absorbing a single photon. The time-dependent Schrödinger equation of H$_2^+$ is numerically solved in {the multipolar} gauge in which the electric quadrupole term and the magnetic dipole term are explicitly expressed. This allows us to separate the contributions of the two terms in the momentum transfer. For different configurations of the molecular and the laser orientation, the transferred momentum to the electron is evaluated at different internuclear distances with various photon energies { and two-center interferences are identified in the whole region. At small electron energies and small internuclear distances, we find significant deviations from the prediction of the classical double-slit model due to the strong mediation of the Coulomb potential.} Finally, even for a large internuclear distance, our results show that a varying molecular scattering phase is important at all electron energies, which is beyond the simple prediction of the linear combination of the atomical orbitals.

physics.atom-ph↗

arXiv2018

Accurate in situ Measurement of Ellipticity Based on Sub-cycle Ionization Dynamics

Elliptically polarized laser pulses (EPLPs) are widely applied in many fields of ultrafast sciences, but the ellipticity~($\varepsilon$) has never been in situ measured in the interaction zone of the laser focus. In this work, we propose and realize a robust scheme to retrieve the $\varepsilon$ by temporally overlapping two identical counter-rotating EPLPs. The combined linearly electric field is coherently controlled to ionize Xe atoms by varying the phase delay between the two EPLPs. The electron spectra of the above-threshold ionization and the ion yield are sensitively modulated by the phase delay. We demonstrate that these modulations can be used to accurately determine $\varepsilon$ of the EPLP. We show that the present method is highly reliable and is applicable in a wide range of laser parameters. The accurate retrieval of $\varepsilon$ offers a better characterization of a laser pulse, promising a more delicate and quantitative control of the sub-cycle dynamics in many strong field processes.

physics.atom-ph↗

arXiv2018

Nondipole effects in atomic dynamic interference

Nondipole effects in the atomic dynamic interference are investigated by numerically solving the time-dependent Schrödinger equation~(TDSE) of hydrogen. It is found that the inclusion of nondipole corrections in the TDSE can induce momentum shifts of photoelectrons in the opposite direction of the laser propagation. The magnitude of the momentum shift is roughly proportional to the laser peak intensity and to the momentum component of the photoelectron along the laser propagation. By including the nondipole corrections of the Volkov phase into a semi-analytical model previously developed under the dipole approximation, all the main features of the momentum shifts can be nicely reproduced. Through an analytic expression, the origin of such momentum shifts is attributed to the nondipole phase difference between the two electron wave packets ejected in the rising edge and the falling edge, which will interfere with each other and result in the final fringe pattern. One important consequence of such momentum shifts is that they can smooth out the peak splitting induced by the dynamic interference in the photoelectron energy spectrum. Nevertheless, it should be emphasized that the dynamic interference persists in the photoelectron momentum distributions and is not suppressed at all for the laser parameters considered in this work.

physics.atom-ph↗

arXiv2017

Localizing High-Lying Rydberg Wave Packets with Two-Color Laser Fields

We demonstrate control over the localization of high-lying Rydberg wave packets in argon atoms with phase-locked orthogonally polarized two-color (OTC) laser fields. With a reaction microscope, we measured ionization signals of high-lying Rydberg states induced by a weak dc field and black-body radiation as a function of the relative phase between the two-color fields. We find that the dc-field ionization yields of high-lying Rydberg argon atoms oscillate with the relative two-color phase with a period of $2π$ while the photoionization signal by black-body radiation shows a period of $π$. These observations are a clear signature of the asymmetric localization of electrons recaptured into high-lying Rydberg states after conclusion of the laser pulse and are supported by a semiclassical simulation of argon-OTC laser interaction. Our findings thus open an effective pathway to control the localization of high-lying Rydberg wave packets.

physics.atom-ph↗

arXiv2014

Attosecond streaking of Cohen-Fano interferences in the photoionization of H$_2^+$

We present the first numerical simulation of the time delay in the photoionization of the simplest diatomic molecule H$_2^+$ as observed by attosecond streaking. We show that the strong variation of the Eisenbud-Wigner-Smith time delay as a function of energy and emission angle becomes observable in the streaking time shift provided laser field-induced components are accounted for. The strongly enhanced photoemission time shifts are traced to destructive Cohen-Fano (or two-center) interferences. Signatures of these interferences in the streaking trace are shown to be enhanced when the ionic fragments are detected in coincidence.

physics.atom-ph↗

arXiv2006

Extreme UV generation from molecules in intense Ti:Sapphire light

We simulate the dynamics of H2+ and HD+ by direct solution of the time-dependent Schroedinger equation for the electronic and nuclear motion for the interaction of intense femtosecond pulses. On these timescales the rotational motion, even for such light molecules, is frozen. Therefore it is a reasonable assumption that the nuclear alignment is fixed during the pulse interaction and that rotation can be neglected. In terms of vibrational relaxation, and since the nuclei are light, vibration will be important over femtosecond timescales. Although homonuclear diatomics are IR-inactive, in an intense field one can create vibrational excitation through continuum coupling. To show the effect of vibration, consider a first approximation in which the nuclei are infinitely massive so they maintain their positions at a fixed bond length of R=2 a.u., throughout the process.

physics.atom-ph↗

arXiv2006

Quantum Spectra of Hydrogen Atoms in Various Magnetic Fields with the Closed Orbit Theory

The quantum spectra of hydrogen atoms in various magnetic fields have been calculated with the closed orbit theory. The magnitude of the magnetic field decreases from 5.96 T to 0.56T with a step of 0.6T. We demonstrate schematically that the closed orbits disappear with the decrease of the magnitude of the magnetic field when the corresponding finite resolution of experiment is fixed. This may give us a good way to control the shape and the number of the closed orbits in the system, and thus to control where a peak should exist in the Fourier transformation of the quantum spectra.

physics.atom-ph↗

arXiv2006

Photodetachment of H$^{-}$ by a Short Laser Pulse in Crossed Static Electric and Magnetic Fields

We present a detailed quantum mechanical treatment of the photodetachment of H$^{-}$ by a short laser pulse in the presence of crossed static electric and magnetic fields. An exact analytic formula is presented for the final state electron wave function (describing an electron in both static electric and magnetic fields and a short laser pulse of arbitrary intensity). In the limit of a weak laser pulse, final state electron wave packet motion is examined and related to the closed classical electron orbits in crossed static fields predicted by Peters and Delos [Phys. Rev. A \textbf{47}, 3020 (1993)]. Owing to these closed orbit trajectories, we show that the detachment probability can be modulated, depending on the time delay between two laser pulses and their relative phase, thereby providing a means to partially control the photodetachment process. In the limit of a long, weak pulse (i.e., a monochromatic radiation field) our results reduce to those of others; however, for this case we analyze the photodetachment cross section numerically over a much larger range of electron kinetic energy (i.e., up to 500 cm$^{-1}$) than in previous studies and relate the detailed structures both analytically and numerically to the above-mentioned, closed classical periodic orbits.

physics.atom-ph↗

arXiv2006

An Efficient and Accurate Grid Method for Solving the Time-Dependent Schroedinger Equation: Application of Coulomb Wave Function DVR to Atomic Systems in Strong Laser Fields

We present an efficient and accurate grid method for solving the time-dependent Schrödinger equation of atomic systems interacting with intense laser pulses. As usual, the angular part of the wave function is expanded in terms of spherical harmonics. Instead of the usual finite difference (FD) scheme, the radial coordinate is discretized using the discrete variable representation which is constructed from the Coulomb wave function. For an accurate description of the ionization dynamics of atomic systems, the Coulomb wave function discrete variable representation (CWDVR) method needs 3-10 times less grid points than the FD method. The resultant grid points of CWDVR distribute unevenly so that one has finer grid near the origin and coarser one at larger distances. The other important advantage of the CWDVR method is that it treats the Coulomb singularity accurately and gives a good representation of continuum wave functions. The time propagation of the wave function is implemented using the well-known Arnoldi method. As examples, the present method is applied to the multiphoton ionization of both H and H$^-$ in intense laser fields. Short-time excitation and ionization dynamics of H by static electric fields is also investigated. For a wide range of photon energies and laser intensities, ionization rates calculated using this method are in excellent agreement with those from other theoretical calculations.

physics.atom-ph↗