Quantum Dynamics Research Articles

State-to-State Time-Dependent Quantum Dynamics Studies of the Si(3P) + OH(X 2Π) → OSi(X 1Σg+) + H(2S) Reaction Based on a New HOSi(X2A') Potential Energy Surface.

Quantum and quasi-classical dynamics calculations were conducted for the reaction of Si with OH on the latest potential energy surface (PES), which is obtained by fitting tens of thousands of ab initio energy points by using the many-body expansion formula. To obtain an accurate PES, all energy points calculated with aug-cc-pVQZ and aug-cc-pV5Z basis sets were extrapolated to the complete basis set limit. The accuracy of our new PES was verified by comparing the topographic characteristics and contour maps of potential energy with other works. In addition, the anharmonic vibrational frequencies of HOSi and HSiO based on the present ab initio and PES by means of quantum dynamics methods were calculated. Dynamics information such as reaction probability, integral cross sections (ICS), product distribution, and rate constants was obtained on the new HOSi(X2A') PES. The dynamic information calculated using the quasi-classical trajectory method and time-dependent wave packet method is generally in good agreement, except for the vibrational state-resolved ICSs of product. The calculated differential cross section and capture time reveal that the reaction is primarily governed by the complex formation mechanism.

Unambiguous simulation of diffusive charge transport in disordered nanoribbons

Charge transport in disordered two-dimensional (2D) systems showcases a myriad of unique phenomenologies that highlight different aspects of the underlying quantum dynamics. Electrons in such systems undergo a crossover from ballistic propagation to Anderson localization, contingent on the system’s effective coherence length. Between the extended and localized phases lies a diffusive crossover in which the charge conductivity is properly defined. The numerical observation of this regime has remained elusive because it requires fully coherent transport to be simulated in systems whose dimensions are sufficiently large to meaningfully split the mean-free path and localization length scales. To address this challenge, we employed a novel linear scaling time-resolved approach that enabled us to derive the dc-transport characteristics and observe the three expected 2D transport regimes — ballistic, diffusive, and localized.

Hyperthermophilic xylanase and thermophilicity analysis by molecular dynamic simulation with quantum mechanics

Thermophilic xylanases catalyzing the cleavage of β-1,4-glycosidic bonds in xylan have applications in food, feed, biorefinery, and pulp industries. In this study, a hyperthermophilic endo-xylanase was obtained by further enhancement of thermal tolerance of a thermophilic GH11 xylanase originated from metagenome of bagasse pile based on rational design. Introducing N13F and Q34L to the previously reported X11P enzyme shifted the optimal working temperature to 85 °C and led to 20.7-fold improvement in thermostability at 90 °C along with a marked increase in Tm to 93.3 °C. X11PNQ enzyme converted xylan to prebiotic xylooligosaccharides with high specificity on xylobiose to xylohexaose and high operational stability at 85 °C, resulting in 10.3-folds yield improvement compared to the parental enzyme. Molecular dynamic simulation and quantum mechanical analysis revealed improved H-bonding networks within GH11 xylanase principal domains and greater dynamic cross-correlations. A novel thermostabilization mechanism by π-amide interaction with slightly lower interaction energy than the native H-bond, but compensated by increased occurrence frequency was firstly demonstrated for thermophilic enzymes. The enzyme represents one of the most thermostable xylanases ever reported with biotechnological potential.Key points• Hyperthemophilic xylanase X11PNQ was obtained by rational design engineering.• X11PNQ showed specificity to prebiotic xylooligosaccharides (XOS) at 85 °C with improved t1/2 at 90 °C.• Novel thermostabilization by π-amide interaction was demonstrated by MD/QM.

Non-linearity and chaos in the kicked top

Classical chaos arises from the inherent non-linearity of dynamical systems. However, quantum maps are linear; therefore, the definition of chaos is not straightforward. To address this, we study a quantum system that exhibits chaotic behavior in its classical limit: the kicked top model, whose classical dynamics are governed by Hamilton’s equations on phase space, whereas its quantum dynamics are described by the Schrödinger equation in Hilbert space. We explore the critical degree of non-linearity signifying the onset of chaos in the kicked top by modifying the original Hamiltonian so that the non-linearity is parameterized by a quantity p. We find two distinct behaviors of the modified kicked top depending on the value of p. Chaos intensifies as p varies within the range of 1≤p≤2, whereas it diminishes for p>2, eventually transitioning to a purely regular oscillating system as p tends to infinity. We also comment on the complicated phase space structure for non-chaotic dynamics. Our investigation sheds light on the relationship between non-linearity and chaos in classical systems, offering insights into their dynamical behavior.

Isolating the classical and quantum coherence of a multiphoton system

The classical properties of thermal light fields were instrumental in shaping our early understanding of light. Before the invention of the laser, thermal light was used to investigate the wave-particle duality of light. The subsequent formulation of the quantum theory of electromagnetic radiation later confirmed the classical nature of thermal light fields. Here, we fragment a pseudothermal field into its multiparticle constituents to demonstrate that it can host multiphoton dynamics mediated by either classical or quantum properties of coherence. This is shown in a forty-particle system through a process of scattering mediated by twisted paths endowed with orbital angular momentum. This platform enables accurate projections of the scattered pseudothermal system into isolated multiphoton subsystems governed by quantum dynamics. Interestingly, the isolated multiphoton subsystems exhibiting quantum coherence produce interference patterns previously attributed to entangled optical systems. As such, our work unveils novel mechanisms to isolate quantum systems from classical fields. This possibility opens new paradigms in quantum physics with enormous implications for the development of robust quantum technologies.

Two-time measurement of entropy transfer in Markovian quantum dynamics

Two-time measurement of entropy transfer in Markovian quantum dynamics

Benchmarking quantum computer simulation software packages: State vector simulators

Rapid advances in quantum computing technology lead to an increasing need for software simulators that enable both algorithm design and the validation of results obtained from quantum hardware. This includes calculations that aim at probing regimes of quantum advantage, where a quantum computer outperforms a classical computer in the same task. High performance computing (HPC) platforms play a crucial role as today’s quantum devices already reach beyond the limits of what powerful workstations can model, but a systematic evaluation of the individual performance of the many offered simulation packages is lacking so far. In this Technical Review, we benchmark several software packages capable of simulating quantum dynamics with a special focus on HPC capabilities. We develop a containerized toolchain for benchmarking a large set of simulation packages on a local HPC cluster using different parallelisation capabilities, and compare the performance and system size-scaling for three paradigmatic quantum computing tasks. Our results can help finding the right package for a given simulation task and lay the foundation for a systematic community effort to benchmark and validate upcoming versions of existing and also newly developed simulation packages.

Dynamic quantum session key agreement protocol based on d-level mutually unbiased bases

Dynamic quantum session key agreement protocol based on d-level mutually unbiased bases

Maximum Entropy Principle in Deep Thermalization and in Hilbert-Space Ergodicity

We report universal statistical properties displayed by ensembles of pure states that naturally emerge in quantum many-body systems. Specifically, two classes of state ensembles are considered: those formed by (i) the temporal trajectory of a quantum state under unitary evolution or (ii) the quantum states of small subsystems obtained by partial, local projective measurements performed on their complements. These cases, respectively, exemplify the phenomena of “Hilbert-space ergodicity” and “deep thermalization.” In both cases, the resultant ensembles are defined by a simple principle: The distributions of pure states have maximum entropy, subject to constraints such as energy conservation, and effective constraints imposed by thermalization. We present and numerically verify quantifiable signatures of this principle by deriving explicit formulas for all statistical moments of the ensembles, proving the necessary and sufficient conditions for such universality under widely accepted assumptions, and describing their measurable consequences in experiments. We further discuss information-theoretic implications of the universality: Our ensembles have maximal information content while being maximally difficult to interrogate, establishing that generic quantum state ensembles that occur in nature hide (scramble) information as strongly as possible. Our results generalize the notions of Hilbert-space ergodicity to time-independent Hamiltonian dynamics and deep thermalization from infinite to finite effective temperature. Our work presents new perspectives to characterize and understand universal behaviors of quantum dynamics using statistical and information-theoretic tools. Published by the American Physical Society 2024

Ultrafast carrier dynamics in InGaN quantum well channel based high electron mobility transistor structure

Ultrafast pump probe measurements on InGaN quantum well (QW) channel based high electron mobility transistor (HEMT) structure enable a direct measurement of the transit/capture time of electrons from GaN buffer layer to InGaN channel layer. Carrier capture time of 75 ± 10 fs is measured and the same is found to be independent of excitation wavelength. However, the capture process is delayed by 160 ± 5 fs when carriers are excited in GaN buffer layer. This happens due to the inclusion of transit time of carriers in GaN layer. It is confirmed by varying the wavelength of excitation where a delay in carrier transit is seen at longer wavelength. It is also seen that the strength of a feature associated with the carriers excited in GaN layer and captured by InGaN QW channel layer mimics the absorption spectrum of GaN, which also confirms that the delay in capture process is caused by the carriers excited in GaN layer. It is found that the capture process can be delayed even up to 240 ± 5 fs when the pump wavelength is kept at 390 nm. It is explained by considering the absorption in a deeper part of GaN layer and via the shallow defect states. Further, it is found that the localization of carriers in InGaN QW channel layer occurs at the time scales of 85 ± 10 fs. The transit/capture/localization time parameters reported in this work provide a crucial set of information, which is essential for modulating the carrier dynamics in InGaN/GaN based HEMTs and other high speed optoelectronic devices.

Role of chirality in photoinduced electron transfer in pentapeptide (L)-His-(L/D)-Asp-(L/D)-Ser-Gly-(L)Tyr in solutions

Factors governing electron transfer (ET) in proteins and peptides are widely studied due to the role of ET in biologically important processes. One of them is the influence of the optical configuration of amino acids on the ability of peptides to aggregate into ensembles: dimers, oligomers, fibrils. Such assemblies, called amyloids, are known to contain D-isomers of asparagine and serine, and their presence in aging living organisms leads to a number of diseases, including Alzheimer’s disease. However, how these amino acids affect the structure and properties of peptides have not yet been established. Using the example of the pentapeptide (PP)-(L)histidine-(L)asparagine-(L)serine-glycine-(L)tyrosine and its analogues with D-asparagine and D-serine, this article studies the comparative reactivity of optical isomers in photoinduced ET using chemically induced dynamic nuclear polarization (CIDNP), fluorescence spectroscopy and quantum chemical calculations. The CIDNP method was chosen because it had previously demonstrated high sensitivity to ET processes in chiral dyads linked by non-covalent interactions. ET involving Tyr and His residues of PP was detected under UV irradiation both in the presence of an electron acceptor, naproxen, and during photolysis of PP itself. It was shown that the efficiency of ET and PP fluorescence quenching differ for optical isomers of asparagine and serine. In addition, the dependence of the CIDNP efficiency on the PP concentration showed that ET between Tyr and peptide bonds can occur in the dimer of the PP. Quantum chemical calculation confirm the possibility of PP self-association.

Nuclear Quantum Effects in Quantum Mechanical/Molecular Mechanical Free Energy Simulations of Ribonucleotide Reductase.

The enzyme ribonucleotide reductase plays a critical role in DNA synthesis and repair. Its mechanism requires long-range radical transfer through a series of proton-coupled electron transfer (PCET) steps. Nuclear quantum effects such as zero-point energy, proton delocalization, and hydrogen tunneling are known to be important in PCET. We present a strategy for efficiently incorporating nuclear quantum effects into multidimensional free energy surfaces and real-time dynamical simulations for condensed-phase systems such as enzymes. This strategy is based on the nuclear-electronic orbital (NEO) method, which treats specified protons quantum mechanically on the same level as the electrons. NEO density functional theory (NEO-DFT) is combined with the quantum mechanical/molecular mechanical finite temperature string method with umbrella sampling via a simple reweighting procedure. Application of this strategy to PCET between two tyrosines, Y731 and Y730, in ribonucleotide reductase illustrates that nuclear quantum effects could either raise or lower the free energy barrier, leading to a range of possible kinetic isotope effects. Real-time time-dependent DFT (RT-NEO-TDDFT) simulations highlight nuclear-electronic quantum dynamics. These approaches enable the incorporation of nuclear quantum effects into a wide range of chemically and biologically important processes.

Output feedback control of LTI systems using quantized periodic event-triggering and 1-bit data transmission

This paper presents a novel framework for periodic event-triggered control (PETC) coupled with dynamic quantization for linear systems. Unlike traditional time-driven control methods, our approach leverages event-based mechanisms to judiciously update control actions, thus minimizing computational load and network traffic. We introduce a two-level dynamic quantizer for encoding feedback information with a single bit, thereby enhancing resource efficiency. The proposed PETC mechanism decides the transmission instants based on the quantized output samples. The resulting system is modeled as a hybrid dynamical system to capture both continuous and discrete dynamics. Sufficient conditions for ensuring the stability of the closed-loop system are presented in the form of a linear matrix inequality. Through numerical simulations, we demonstrate that our approach captures the initial output within a finite time and significantly reduces data transmissions compared to traditional methods. This paper makes key contributions in the integration of dynamic quantization with PETC, leading to resource-efficient and stable control systems.

Theoretical Study on Singlet Fission Dynamics and Triplet Migration Process in Symmetric Heterotrimer Models.

Singlet fission (SF) is a photophysical process where one singlet exciton splits into two triplet excitons. To construct design guidelines for engineering directional triplet exciton migration, we investigated the SF dynamics in symmetric linear heterotrimer systems consisting of different unsubstituted or 6,13-disubstituted pentacene derivatives denoted as X/Y (X, Y: terminal and center monomer species). Time-dependent density functional theory (TDDFT) calculations clarified that the induction effects of the substituents, represented as Hammett's para-substitution coefficients σp, correlated with both the excitation energies of S1 and T1 states, in addition to the energies of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO). Electronic coupling calculations and quantum dynamics simulations revealed that the selectivity of spatially separated TT states for heterotrimers increased over 70%, superior to that in the homotrimer: an optimal region of the difference in σp between the substituents of X and Y for the increase in SF rate was found. The origin of the rise in SF rate is explained by considering the quantum interference effect: reduction in structural symmetry opens new interaction paths, allowing the S1-TT mixing, which contributes to accelerating the hetero-fission between the terminal and center molecules.

Simulating passage through a cascade of conical intersections with collapse-to-a-block molecular dynamics

The Ehrenfest with collapse-to-a-block (TAB) molecular dynamics approach was recently introduced to allow accurate simulation of nonadiabatic dynamics on many electronic states. Previous benchmarking work has demonstrated it to be highly accurate for modelling dynamics in one-dimensional analytical models, but nonadiabatic dynamics often involves conical intersections, which are inherently two-dimensional. In this report, we assess the performance of TAB on two-dimensional models of cascades of conical intersections in dense manifolds of states. Several variants of TAB are considered, including TAB-w, which is based on the assumption of a Gaussian rather than exponential decay of the coherence, and TAB-DMS, which incorporates an efficient collapse procedure based on approximate eigenstates. Upon comparison to numerically exact quantum dynamics simulations, it is found that all TAB variants provide a suitable description of the dynamical passage through a cascade of conical intersections. The TAB-w approach is found to provide a somewhat more accurate description of population dynamics than the original TAB method, with final absolute population errors ≤ 0.013 in all cases. Even when only four approximate eigenstates are computed, the use of approximate eigenstates was found to introduce minimal additional error (absolute population error ≤ 0.018 in all models).

Cavity induced modulation of intramolecular vibrational energy flow pathways.

Recent experiments in polariton chemistry indicate that reaction rates can be significantly enhanced or suppressed inside an optical cavity. One possible explanation for the rate modulation involves the cavity mode altering the intramolecular vibrational energy redistribution (IVR) pathways by coupling to specific molecular vibrations in the vibrational strong coupling (VSC) regime. However, the mechanism for such a cavity-mediated modulation of IVR is yet to be understood. In a recent study, Ahn et al. [Science 380, 1165 (2023)] observed that the rate of alcoholysis of phenyl isocyanate (PHI) is considerably suppressed when the cavity mode is tuned to be resonant with the isocyanate (NCO) stretching mode of PHI. Here, we analyze the quantum and classical IVR dynamics of a model effective Hamiltonian for PHI involving the high-frequency NCO-stretch mode and two of the key low-frequency phenyl ring modes. We compute various indicators of the extent of IVR in the cavity-molecule system and show that tuning the cavity frequency to the NCO-stretching mode strongly perturbs the cavity-free IVR pathways. Subsequent IVR dynamics involving the cavity and the molecular anharmonic resonances lead to efficient scrambling of an initial NCO-stretching overtone state over the molecular quantum number space. We also show that the hybrid light-matter states of the effective Hamiltonian undergo a localization-delocalization transition in the VSC regime.

Quantum real-time evolution of entanglement and hadronization in jet production: Lessons from the massive Schwinger model

The possible link between entanglement and thermalization, and the dynamics of hadronization are addressed by studying the real-time response of the massive Schwinger model coupled to external sources. This setup mimics the production and fragmentation of quark jets, as the Schwinger model and quantum chromodynamics (QCD) share the properties of confinement and chiral symmetry breaking. By using simulations of quantum dynamics on classical hardware, we study the entanglement between the produced jets, and observe the growth of the corresponding entanglement entropy in time. This growth arises from the increased number of contributing eigenstates of the reduced density matrix with sufficiently large and close eigenvalues. We also investigate the physical nature of these eigenstates, and find that at early times they correspond to fermionic Fock states. We then observe the transition from these fermionic Fock states to mesonlike bound states as a function of time. In other words, we observe how hadronization develops in real time. At late times, the local observables at midrapidity (such as the fermion density and the electric field) approach approximately constant values, suggesting the onset of equilibrium and approach to thermalization. Published by the American Physical Society 2024

Quantum rotational dynamics of linear C5 at low interstellar temperatures for H2 collision.

The quantum dynamics of carbon chains through H2 and He collisions in the interstellar medium (ISM) is an important step toward accurate modeling of their abundance in non-local thermodynamic equilibrium conditions. The C5(Σg+1) molecule is the longest pure carbon chain detected in the ISM to date. While He collisions are computationally easy to perform, the collision with much more abundant H2 is both complicated and computationally demanding. Using templates for approximating p-H2 collisional rates, such as scaling He rates and using a reduced 4D → 2D potential energy surface (PES), has limited applicability. On the other hand, any such approximation does not exist for o-H2. Therefore, a full rotational dynamics of C5 with both p- and o-H2 is performed considering both molecules as rigid-rotors. The PES is calculated using CCSD(T)-F12a/AVTZ, and a neural network fitting model has been carefully chosen to strictly obey spectroscopic accuracy and augment the PES. The augmented PES is then expanded into radial terms using the bispherical harmonics function, and close coupling calculations have been done to get the cross sections and, subsequently, rate coefficients for various rotational transitions of C5.

Lissajous dynamics of a quantum particle in a tilted two-dimensional discrete lattice

The quantum dynamics of a single particle in a discrete two-dimensional tilted lattice is analyzed from the perspective of the classical-quantum correspondence. Utilizing the fact that tilting the lattice results in oscillatory dynamics, we show how the parameters of the lattice and the initial state of the particle can be tuned so that during evolution the probability distribution does not change its shape, while its center follows the trajectory known in classical mechanics as Lissajous curves.

Toward a Correct Description of Initial Electronic Coherence in Nonadiabatic Dynamics Simulations.

The recent improvement in experimental capabilities for interrogating and controlling molecular systems with ultrafast coherent light sources calls for the development of theoretical approaches that can accurately and efficiently treat electronic coherence. However, the most popular and practical nonadiabatic molecular dynamics techniques, Tully's fewest-switches surface hopping and Ehrenfest mean-field dynamics, are unable to describe the dynamics proceeding from an initial electronic coherence. While such issues are not encountered with the analogous coupled-trajectory algorithms or numerically exact quantum dynamics methods, applying such techniques necessarily comes with a higher computational cost. Here we show that a correct description of initial electronic coherence can indeed be achieved using independent-trajectory methods derived from the semiclassical mapping formalism. The key is the introduction of an initial sampling over the electronic phase space and a means of incorporating phase interference between trajectories, both of which are naturally achieved when working within the semiclassical mapping framework.