Quantum Effects Research Articles

Cosmic entanglement sudden birth: expansion-induced entanglement in hydrogen atoms

Hydrogen is the most dominant atom in the universe and is considered the main component of baryonic matter. Thus far, the quantum features of the unbounded hydrogen atoms in the background of the universe and the possibility of emerging unique quantum effects, such as entanglement on the cosmological scale, have not been considered. In this work, we demonstrate that the dynamical expansion of the universe leads to the emergence of natural entanglement in the hyperfine structure of atomic hydrogen. Our findings reveal that there exists a critical age for the universe where hydrogen atoms naturally build up entanglement, resulting from the expansion of the universe. More precisely, when the universe reaches the age of about 2.5 × 1018 seconds (about 80 billion years old), the hyperfine structure entanglement in hydrogen atoms naturally takes off, demonstrating a peculiar quantum phenomenon known as entanglement sudden birth. This expansion-induced entanglement becomes maximum at about 3.6 × 1018 seconds (about 115 billion years), after the Big Bang. By analyzing the fate of seed atoms formed in the early universe, this study underscores the significance of unique quantum mechanical features, such as entanglement, on cosmological scales.

Interface engineering of van der Waals heterostructures towards energy-efficient quantum devices operating at high temperatures

Abstract Quantum devices, which rely on quantum mechanical effects for their operation, may offer advantages, such as reduced dimensions, increased speed, and energy efficiency, compared to conventional devices. However, quantum phenomena are typically observed only at cryogenic temperatures, which limits their practical applications. Two-dimensional materials and their van der Waals (vdW) heterostructures provide a promising platform for high-temperature quantum devices owing to their strong Coulomb interactions and/or spin-orbit coupling. In this review, we summarise recent research on emergent quantum phenomena in vdW heterostructures based on interlayer tunnelling and the coupling of charged particles and spins, including negative differential resistance, Josephson tunnelling, exciton condensation, and topological superconductivity. These are the underlying mechanisms of energy-efficient devices, including tunnel field-effect transistors, topological/superconducting transistors, and quantum computers. The natural homojunction within vdW layered materials offers clean interfaces and perfectly aligned structures for enhanced interlayer coupling. Twisted bilayers with small angles may also give rise to novel quantum effects. In addition, we highlight several proposed structures for achieving high-temperature Majorana zero modes, which are critical elements of topological quantum computing. This review is helpful for researchers working on interface engineering of vdW heterostructures towards energy-efficient quantum devices operating above the liquid nitrogen temperature.

Review of: "the electrons and photons in nanowires experience "confined quantum effects.""

Review of: "the electrons and photons in nanowires experience "confined quantum effects.""

NUMERICAL METHOD FOR SOLVING OF THE DIFFRACTION PROBLEM DESCRIBED BY MAXWELL’S EQUATIONS WITH MESOSCOPIC BOUNDARY CONDITIONS

A numerical method for solving the diffraction boundary problem for the system of Maxwell’s equations with mesoscopic boundary conditions has been developed and implemented. It is based on the discrete source method. A numerical analysis of the influence of surface quantum effects on the optical characteristics of plasmonic nanoparticles is carried out. It has been established that surface effects have a significant impact on the field characteristics, and the results differ significantly from the case of volumetric effects.

Role of magnetic doping in topological HgTe and application of the Gram–Schmidt method for computing impurity states in quantum wells

Abstract The quantum spin Hall effect in non-magnetic and Mn-doped HgTe quantum well (QW) is strongly affected by Kondo scattering of edge electrons by holes localized on acceptors. A generalized eigenvalue method is usually employed for determining impurity binding energies from the multiband Kohn–Luttinger Hamiltonians in bulk samples and semiconductor quantum structures. Such an approach provides accurate values of the level positions but its applicability for determining the impurity localization radius can be questioned. As an alternative method we propose here the Gram–Schmidt orthogonalization procedure allowing to employ the standard eigenvalue algorithms and, thus, to determine both impurity level energies and the set of normalized eigenvectors. We apply this approach to singly-ionized acceptor states in HgTe QWs and obtain impurity level energies and localization radiuses even for states degenerate with the continuum of band states. Such information allows us to assess the energy of bound magnetic polarons in QWs doped with magnetic ions. We determine the polaron energies and discuss consequences of the resonant polaron formation on band transport in the bulk samples and QWs in the regimes of quantum Hall effects.

OPTICAL PROPERTIES OF THE AgBiP2Se6 SINGLE CRYSTAL

The AgBiP2Se6 compound has emerged as one of the most studied hexachalcohypodiphosphates in recent years. This is interest is driven by its distinctive layered structure, which implies the possibility of obtaining monolayers and the observation of various of quantum effects. Most studies to date, however, have focused on first-principles calculations, while experimental investigations have primarily been limited to structural analysis and stoichiometric composition determination. This work partially addresses the gap in research by exploring the optical properties of AgBiP2Se6. Transmission spectra within the optical range of 220-1400 nm, as well as Raman spectra, were obtained from single crystalline AgBiP2Se6 samples. The band gap, determined from the transmission spectra using the graphical Tauc method, was found to be 1.44 eV. This value aligns closely with the DFT band-structure calculations using the Perdue-Burke-Erzenhorf (PBE) model without a Hubbard correction parameter (1.384 eV). The Raman spectrum of the AgBiP2Se6 crystal reveals five distinct peaks at approximately 68, 125, 169, 436, and 462 cm-1. The peak at 68 cm-1 can be attributed to the vibrational mode of the cationic centers; the peaks at 125 and 169 cm-1 can correspond to deformations within the Se-P-P and Se-P-Se bonding systems involving changes in bond angles; and the peaks at 436 and 462 cm-1 reflect bond length changes within the anionic (P2Se6)4-group.

Quantum tunneling of fermions from kerr-like black holes within topologically massive gravity

In the framework of 3-D general relativity, this study explores a Kerr-like black hole solution with a focus on its causal structure and particle dynamics, employing Penrose diagrams to elucidate the spacetime geometry. The research investigates the behavior pf particles in the vicinity of the event horizon, analyzing their trajectories and potential fates, including the influence of the black hole’s rotation and gravitational effects. The Dirac equation is solved in this curved spacetime using “WKB approximation”, allowing the computation of the Hawking temperature and unveiling quantum effects associated with black hole geometries in three dimensions. Moreover, the phenomenon of superradiance is explored, highlighting the mechanisms through with the rotational energy and angular momentum of the black hole are extracted. This phenomenon provides deeper insights into energy transfer processes and the stability of such black hole solutions. The research contributes to a better understanding of black hole thermodynamics, particularly in lower-dimensional gravitational settings, and offers a comprehensive analysis of energy exchange processes. By integrating classical and quantum perspectives, this study enhances the comprehension of particle dynamics, quantum field behavior, and thermodynamic properties of black holes, enriching the broader field of lower-dimensional gravitational models and their implications for fundamental physics.

Kasner eons in Lovelock black holes

In the vicinity of spacelike singularities, general relativity predicts that the metric behaves, at each point, as a Kasner space which undergoes a series of “Kasner epochs” and “eras” characterized by certain transition rules. The period during which this process takes place defines a “Kasner eon,” which comes to an end when higher-curvature or quantum effects become relevant. When higher-curvature densities are included in the action, spacetime can undergo transitions into additional Kasner eons. During each eon, the metric behaves locally as a Kasner solution to the higher-curvature density controlling the dynamics. In this paper we identify the presence of Kasner eons in the interior of static and spherically symmetric Lovelock gravity black holes. We determine the conditions under which eons occur and study the Kasner metrics which characterize them, as well as the transitions between them. We show that the null energy condition implies a monotonicity property for the effective Kasner exponent at the end of the Einsteinian eon. We also characterize the Kasner solutions of more general higher-curvature theories of gravity. In particular, we observe that the Einstein gravity condition that the sum of the Kasner exponents adds up to 1, ∑i=1D−1pi=1, admits a universal generalization in the form of a family of Kasner metrics satisfying ∑i=1D−1pi=2n−1 which exists for any order-n higher-curvature density and in general dimensions. Published by the American Physical Society 2024

Counterintuitive Scenarios in Discrete Gravity Without Quantum Effects or Causality Violations

In certain established approaches to quantum gravity, such as causal set theory and causal dynamical triangulations, discrete spacetime structure is taken to be a primary feature, not a secondary effect of “quantizing” a pre-existing classical continuum-based theory, as is done in approaches such as string theory and loop quantum gravity. For a priori discrete models, the full quantum theory is often obtained via some version of Feynman’s sum-over-histories approach, in which each “history” is a discrete object viewed as a classical spacetime. Counterintuitive physical scenarios such as Schrödinger’s cat or the grandfather paradox are typically associated with either quantum effects or causality violations, but we demonstrate that equally bizarre scenarios can arise at a purely classical level in the discrete causal context due to symmetry considerations. In particular, the graph-theoretic phenomenon of pseudosimilarity leads to situations in which alternative events occurring at physically distinguishable locations in the universe can cause different parts of the universe to “swap identities” in a fugue-like manner alien to continuum-based theories. This phenomenon is perhaps best understood as an extension of the relativity principle, which we call relativity of identity.

Potential energy landscape formalism for quantum molecular liquids

The potential energy landscape (PEL) formalism is a powerful tool within statistical mechanics to study the thermodynamic properties of classical low-temperature liquids and glasses. Recently, the PEL formalism has been extended to liquids/glasses that obey quantum mechanics, but applications have been limited to atomistic model liquids. In this work, we extend the PEL formalism to liquid/glassy water using path-integral molecular dynamics (PIMD) simulations, where nuclear quantum effects (NQE) are included. Our PIMD simulations, based on the q-TIP4P/F water model, show that the PEL of quantum water is both Gaussian and anharmonic. Importantly, the ring-polymers associated to the O/H atoms in the PIMD simulations, collapse at the local minima of the PEL (inherent structures, IS) for both liquid and glassy states. This allows us to calculate, analytically, the IS vibrational density of states (IS-VDOS) of the ring-polymer system using the IS-VDOS of classical water (obtained from classical MD simulations). The role of NQE on the structural properties of liquid/glassy water at various pressures are discussed in detail. Overall, our results demonstrate that the PEL formalism can effectively describe the behavior of molecular liquids at low temperatures and in the glass states, regardless of whether the liquid/glass obeys classical or quantum mechanics.

Impacts of phosphorus limitation in the toxicity of environmental concentrations of lead and zinc in Raphidocelis subcapitata (Chlorophyceae)

AbstractMicroalgal metabolism is affected by the surrounding environment and nutrients such as phosphorus (P) and nitrogen (N) are essential for optimal metabolism, as well as trace amounts of essential metals such as zinc (Zn); although in higher doses than required, Zn can be toxic. Lead (Pb) is a non-essential metal that can harm organisms from different trophic levels. In the environment, algae are exposed to several stressors simultaneously and adapt their metabolism. In the present study, we evaluated P limitation combined with environmental concentrations of Zn or Pb to the freshwater microalga Raphidocelis subcapitata regarding growth, pigments production, and photosynthetic parameters. Our results indicate that P limitation affected the growth, pigments production, relative maximum electron transport rate (rETRmax), and saturation irradiance; while Pb altered growth, pigments production, and maximum quantum yield; and Zn affected pigment production, photochemical and non-photochemical quenching, and rETRmax. However, the combination of metal and P limitation resulted in synergistic responses, i.e., higher damages than the isolated stressors, in growth, maximum and effective quantum yield, and in the rapid light curve parameters. On the other hand, antagonism, i.e., lower damages than isolated stressors, was observed in pigments production and non-photochemical quenching, suggesting that algae activated defense mechanisms to cope with both stressors simultaneously. In addition, our results indicate an algal metabolism adjustment to P limitation and highlight the importance of considering physicochemical water characteristics when defining regulations of acceptable levels of metals in aquatic ecosystems.

Predictive evaluation of hydrogen diffusion coefficient on Pd(111) surface by path integral simulations using neural network potential

Quantum diffusion of hydrogen (H) on palladium (Pd) (111) was studied using two types of path integral simulations: quantum transition state theory (QTST) and ring polymer molecular dynamics (RPMD). The use of an artificial neural network potential trained by density functional theory calculations has made it feasible to perform path integral simulations considering nuclear quantum effects (NQEs) of a many-body Pd-H system with accuracy. The QTST result has shown a clear non-Arrhenius behavior in the diffusion coefficient (D) of H below the temperature of 150–200 K due to the NQEs. Comparing the D on Pd surface and bulk Pd, it was found that surface and bulk diffusion are competitive at high temperature. Consistent with this, it was observed in the RPMD simulation at 800 K that a part of the quantum trajectories of H on the surface bifurcates to the Pd subsurface. As the temperature decreases, the surface diffusion becomes much faster than the bulk diffusion. Furthermore, distinct quantum behaviors of H were identified at the surface and within the bulk. The D values obtained from this study using a “flexible” Pd surface model differed considerably from those previously reported using “frozen” Pd surface models, indicating an important contribution from Pd vibrations coupled with H diffusion. Published by the American Physical Society 2024

Genome-wide survey of chlorophyllase (CLH) gene family in seven Rosaceae and functional characterization of MdCLH1 in apple (Malus domestica) leaf photosynthesis

Chlorophyll, a crucial pigment in plant photosynthesis, undergoes dynamic synthesis and degradation processes throughout the growth cycle of plants. Chlorophyllase (CLH) plays a crucial role in the degradation of chlorophyll by removing the phytol group from chlorophyll A to produce chlorophyllide A. However, Rosaceae species remain underexplored in terms of understanding the functional divergences among CLH gene family members (CLHs) involved in chlorophyll catabolism and photosynthesis. The apple (Malus domestica) CLHs also requires further systematic characterization and identification. In this study, 20 CLHs (MdCLH1-4, FvCLH1-2, PpCLH1-2, PcCLH1-3, PaCLH1-2, RrCLH1-4, RcCLH1-3) were identified from seven species belonging to the Rosaceae family. The chromosomal distribution of these gene family members is mostly separate across all species, except in Rosa rugosa. The number of amino acids encoded by these genes ranges from 171 aa to 391 aa, possessing a theoretical isoelectric point (PI) of 5.46-9.59, and a relative molecular weight of 18313.07D to 42413.21D. Secondary structure predictions highlight α-helix and random coil conformations as the dominant structural elements of CLH proteins present in Rosaceae species. Subcellular localization predictions indicate that all CLH proteins are expressed in chloroplasts, while MdCLH4 is uniquely localized to the nucleus. Phylogenetic analysis reveals high homology and close evolutionary relationships among the genes in three subfamilies. All these 20 CLHs contain elements responsive to phytohormones, environmental stress, and light. Furthermore, transcriptomic profiling using geneChip expression array coupled with qRT-PCR analyses revealed a heightened transcriptional activity of MdCLHs in leaf tissues and protective tissue of annual shoots as compared to other plant components. Additional experimental evidence specifically indicates MdCLH1 is located in the chloroplasts of tobacco leaves. Notably, MdCLH1 transient expression in apple leaves decreased chlorophyll a, carotenoids, total chlorophyll content, non - photochemical quenching coefficient (NPQ), and intercellular CO₂ concentration (Ci), while increasing chlorophyll b content, effective PSII quantum yield [Y(II)], net photosynthetic rate (Pn), stomatal conductance (Gs), and electron transport rate (ETR). These suggest MdCLH1 enhances light energy conversion in PSII by modulating chlorophyll degradation, potentially improving photosynthetic efficiency and reducing the potential for photoinhibition. This study lays a solid foundation for further exploration into the functional roles of CLHs in the Rosaceae family.

Applications of welded tangleoids to effective quantum field theories (EQFT)

Applications of welded tangleoids to effective quantum field theories (EQFT)

Nuclear Quantum Effects in Liquid Water Are Marginal for Its Average Structure but Significant for Dynamics.

Isotopic substitution, which can be realized in both experiment and computer simulations, is a direct approach to assess the role of nuclear quantum effects on the structure and dynamics of matter. However, the impact of nuclear quantum effects on the structure of liquid water as probed in experiment by comparing normal to heavy water has remained controversial. To settle this issue, we employ a highly accurate machine-learned high-dimensional neural network potential to perform converged coupled cluster-quality path integral simulations of liquid H2O versus D2O at ambient conditions. We find substantial H/D quantum effects on the rotational and translational dynamics of water, in close agreement with the experimental benchmarks. However, in stark contrast to the role for dynamics, H/D quantum effects turn out to be small, on the order of 1/1000 Å, on both average intramolecular and H-bonding structures of water. The most probable structure of water remains nearly unaffected by nuclear quantum effects, but effects on fluctuations away from average are appreciable, rendering H2O substantially more "liquid" than D2O.

Self-learning path integral hybrid Monte Carlo with mixed abinitio and machine learning potentials for modeling nuclear quantum effects in water.

The introduction of machine learned potentials (MLPs) has greatly expanded the space available for studying Nuclear Quantum Effects computationally with abinitio path integral (PI) accuracy, with the MLPs' promise of an accuracy comparable to that of abinitio at a fraction of the cost. One of the challenges in development of MLPs is the need for a large and diverse training set calculated by abinitio methods. This dataset should ideally cover the entire phase space, while not searching this space using abinitio methods, as this would be counterproductive and generally intractable with respect to computational time. In this paper, we present the self-learning PI hybrid Monte Carlo Method using a mixed abinitio and ML potential (SL-PIHMC-MIX), where the mixed potential allows for the study of larger systems and the extension of the original SL-HMC method [Nagai et al., Phys. Rev. B 102, 041124 (2020)] to PI methods and larger systems. While the MLPs generated by this method can be directly applied to run long-time ML-PIMD simulations, we demonstrate that using PIHMC-MIX with the trained MLPs allows for an exact reproduction of the structure obtained from abinitio PIMD. Specifically, we find that the PIHMC-MIX simulations require only 5000 evaluations of the 32-bead structure, compared to the 100 000 evaluations needed for the abinitio PIMD result.

On-shell effective field theory and quantum transport for hard photons

We develop an effective field theory for the description of high energetic or hard photons, the on-shell effective theory (OSEFT). The OSEFT describes the so-called eikonal or semiclassical optical limit, allowing for corrections organized in a systematic expansion on inverse powers of the photon energy. We derive the OSEFT from the Maxwell Lagrangian and study its different properties, such as the gauge symmetry and reparametrization invariance. The theory can be finally formulated in terms of a gauge invariant vector gauge field, without the need to introduce gauge-fixing. We then use the OSEFT to compute corrections to the Wigner photon function and derive its associated side jump effect from reparametrization invariance. Finally, we discuss how to properly define the Stokes parameters from transport theory once quantum effects are considered, so as to preserve their well-defined properties under Lorentz transformations. Published by the American Physical Society 2024

Towards a Unitary Formulation of Quantum Field Theory in Curved Space-Time: The Case of the Schwarzschild Black Hole

Abstract We argue that the origin of unitarity violation and the information loss paradox in our understanding of black holes (BHs) lies in the standard way of doing quantum field theory in curved space-time (QFTCS), which is heavily biased on intuition borrowed from classical general relativity. In this paper, with the quantum-first approach, we formulate a so-called direct-sum QFT (DQFT) in BH space-time based on a novel formulation of discrete space-time transformations in gravity that potentially restores unitarity. By invoking the quantum effects associated with the gravitational backreaction, we show that the Hawking quanta emerging outside of the Schwarzschild radius ($r_S=2GM$) cannot be independent of the quanta that continue to be inside $r_S$. This enables information to be carried by Hawking quanta, but in the BH DQFT formalism, we do not get any firewalls. Furthermore, DQFT leads to the BH evaporation involving only pure states. This means the quantum mechanical effects at the BH horizon produce two components of a maximally entangled pure state in geometric superselection sector Hilbert spaces. This construction enables pure states to evolve into pure states, restoring unitarity and observer complementarity. Finally, we discuss how our framework leaves important clues for formulating a scattering matrix and probing the nature of quantum gravity.

A novel mechanism and model of hydrogen isotope exchange in vacancy considering nuclear quantum effects

Abstract Tritium (T) retention in plasma-facing materials (PFMs) raises significant radiological safety concerns and adversely affects the self-sustained burning of T in fusion reactors. Therefore, the removal of retained T from PFMs has become an urgent task. Hydrogen isotope (HI) exchange has proven to be an effective method for T removal. However, the microscopic mechanisms, particularly the role of isotope effects, remain insufficiently understood. For the first time, this work employs path integral molecular dynamics (PIMD) to account for the nuclear quantum effects of HIs and explore the microscopic mechanisms of HI exchange in tungsten (W) vacancies. Atomic-scale simulations reveal that the fundamental principle of HI exchange is the reduction in binding energy between HIs and vacancies as the defect filling level increases, involving two key processes: de-trapping and trapping. These processes are influenced by isotope effects, with pronounced differences observed at low temperatures. Notably, T exhibits a higher probability of de-trapping from vacancies compared to hydrogen (H), while vacancies demonstrate a stronger affinity for trapping H. In contrast, the isotope effect is less pronounced between deuterium (D) and H, leading to different exchange efficiencies between H and T, as well as between D and T. Based on these isotope effects, we proposed a detailed microscopic mechanism for HI exchange in vacancies and developed a T evolution model that accounts for variations in HI concentrations. This work advances our understanding of HI exchange for T removal applications and offers a more accurate assessment of T retention in future D-T environments.

Effects of Foliar Application of a Lambda-Cyhalothrin Insecticide on Photosynthetic Characteristics of a Fodder Plant Malva moschata

Recently, a large number of pesticides with different chemical structures and modes of action (MOAs) have become regularly used in agriculture. They are used to control the insect populations in various crops. Foliar application of pesticides may negatively affect crop physiology, especially photosynthesis. However, the sensitivity of particular crops, especially their primary and secondary photosynthetic processes, to insecticide application is generally unknown. Our study aimed to evaluate the negative effects of lambda-cyhalothrin (λ-CY) on photosystem II (PSII) in Malva moschata (Musk mallow). We used fast chlorophyll fluorescence transients (i.e., OJIPs) and OJIP-derived parameters, the effective quantum yield of PSII (ΦPSII), induction curves of non-photochemical quenching (NPQ) and spectral reflectance curves and indices. The recommended concentration (0.05 μM) and a 10 times higher concentration (0.5 μM) of λ-CY did not cause any negative effect on photosynthetic parameters. An overdosed foliar application (100 times higher than recommended, i.e., 50 μM) led to changes in OJIP shape; a decrease in performance index (PIABS), maximum photosynthetic yield (FV/FM) and photosynthetic electron transport (ET0/RC); and an increase in protective mechanisms (unregulated quenching, DI0/RC). These changes lasted only tens of minutes after application, after which the parameters returned to pre-application values. An overdosed λ-CY application caused more rapid activation of NPQ, indicating the early response to stress in PSII. The application of 50 μM λ-CY caused an increase in spectral reflectance above 720 nm and changes in the indices that indicated λ-CY-induced stress.