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The study of noise assisted-transport in quantum systems is essential in a wide range of applications, from near-term NISQ devices to models for quantum biology. Here, we study a generalized XXZ model in the presence of stochastic collision noise, which allows describing environments beyond the standard Markovian formulation. Our analysis through the study of the local magnetization, the inverse participation ratio (IPR) or its generalization, and the inverse ergodicity ratio (IER) showed clear regimes, where the transport rate and coherence time could be controlled by the dissipation in a consistent manner. In addition, when considering various excitations, we characterized the interplay between collisions and system interactions, identifying regimes in which transport was counterintuitively enhanced when increasing the collision rate, even in the case of initially separated excitations. These results constitute an example of an essential building block for the understanding of quantum transport in structured noisy and warm-disordered environments.

The sign of six Interactions between microscopic particles are usually described as two-body interactions, although it has been shown that higher order multi-body interactions could give rise to novel quantum phases with intriguing properties. This paper demonstrates effective six-body interactions in a system of ultracold bosonic atoms in a three-dimensional optical lattice. The coherent multi-particle interactions observed here open a new window for simulations of effective field theories and may help to enable the realization of novel topologically ordered many-body quantum phases. Interactions between microscopic particles are usually described as two-body interactions, although it has been shown that higher-order multi-body interactions could give rise to new quantum phases with intriguing properties. Here, effective six-body interactions are demonstrated in a system of ultracold bosonic atoms in a three-dimensional optical lattice. Interactions lie at the heart of correlated many-body quantum phases 1 , 2 , 3 . Typically, the interactions between microscopic particles are described as two-body interactions. However, it has been shown that higher-order multi-body interactions could give rise to novel quantum phases with intriguing properties. So far, multi-body interactions have been observed as inelastic loss resonances in three- and four-body recombinations of atom–atom and atom–molecule collisions 4 , 5 , 6 . Here we demonstrate the presence of effective multi-body interactions 7 in a system of ultracold bosonic atoms in a three-dimensional optical lattice, emerging through virtual transitions of particles from the lowest energy band to higher energy bands. We observe such interactions up to the six-body case in time-resolved traces of quantum phase revivals 8 , 9 , 10 , 11 , using an atom interferometric technique that allows us to precisely measure the absolute energies of atom number states at a lattice site. In addition, we show that the spectral content of these time traces can reveal the atom number statistics at a lattice site, similar to foundational experiments in cavity quantum electrodynamics that yield the statistics of a cavity photon field 12 . Our precision measurement of multi-body interaction energies provides crucial input for the comparison of optical-lattice quantum simulators with many-body quantum theory.

Since the invention of quantum mechanics, even the simplest example of the collisional breakup of a system of charged particles, e$^-$ + H → H$^+$ + e$^-$ + e$^-$ (where e$^-$ is an electron and H is hydrogen), has resisted solution and is now one of the last unsolved fundamental problems in atomic physics. A complete solution requires calculation of the energies and directions for a final state in which all three particles are moving away from each other. Even with supercomputers, the correct mathematical description of this state has proved difficult to apply. A framework for solving ionization problems in many areas of chemistry and physics is finally provided by a mathematical transformation of the Schrödinger equation that makes the final state tractable, providing the key to a numerical solution of this problem that reveals its full dynamics.

The crossing of two electronic potential surfaces (a conical intersection) should result in geometric phase effects even for molecular processes confined to the lower surface. However, recent quantum simulations of the hydrogen exchange reaction (H + H₂ [rightwards arrow] H₂ + H) have predicted a cancellation in such effects when product distributions are integrated over all scattering angles. We used a simple topological argument to extract reaction paths with different senses from a nuclear wave function that encircles a conical intersection. In the hydrogen-exchange reaction, these senses correspond to paths that cross one or two transition states. These two sets of paths scatter their products into different regions of space, which causes the cancellation in geometric phase effects. The analysis should generalize to other direct reactions.

A molecular-dynamics technique for determining the adhesion strength and analyzing diffusion at interfaces between different materials has been developed. The adhesion strength is determined by calculating the adhesive fracture energy defined as the difference between the total potential energy of the material-connected state and that of the material-separated state. This technique is used to determine the adhesion strength and analyze diffusion at the interfaces between Cu films and high-melting-point materials that are used as underlay materials for Cu interconnects in ULSIs. The adhesive fracture energy shows that the adhesion strength of the Cu/Ru and Cu/Ir interfaces is much higher than that of the Cu/W, Cu/TiN, and Cu/Ta interfaces. Because the diffusion of Cu atoms at the Cu/Ru and Cu/Ir interfaces is suppressed, the surface smoothness of Cu films on Ru and Ir is much better than that on W, TiN, and Ta. It is also found that adhesion strength and smoothness increase with decreasing lattice mismatch between Cu and the underlay material. These results are confirmed by SEM (scanning electron microscope) and scratch testing.

Semiclassical theory finds use in chemical physics both as a computational method and as a conceptual framework for interpreting quantum features in experiments and in numerical quantum calculations. The semiclassical description of one-dimensional dynamical systems is essentially a solved problem for eigenvalue and scattering situations and for general topologies of potential functions (simple potential wells, multiple wells, multiple barriers, and so forth). Considerable progress has also been made in generalizing semiclassical theory to multidimensional dynamical systems (such as inelastic and reactive scattering of atoms and molecules and vibrational energy levels of polyatomic molecules), and here, too, it provides a useful picture of quantum features (interference in product state distribution, generalized tunneling phenomena, and others) in these more complex systems.

Differential and integral W-values for ionization in gaseous water for electron and proton irradiation have been analyzed from the theoretical point of view for consistency between ionization and total inelastic collision cross sections. For low-energy electrons, which are ubiquitous for all primary radiations, the experimental or compiled cross sections from different sources are sometimes not consistent with one another. A practical, self-consistent procedure is outlined in such cases. The high-energy asymptotic W-values for differential and integral ionization are calculated to be 33.7 and 34.7 eV, respectively, for electron irradiation and 34.6 and 32.5 eV, respectively, for proton irradiation. The computed variations of the W-values with energy are generally in good agreement with experiment. Integral primary W-values due only to the interactions between the incident particle and the water vapor are calculated to be 43.5 and 45.0 eV for electrons and protons, respectively, in the high-energy asymptotic limit.

Mechanochemical and mechanical alloying processes take place between colliding surfaces in the heavy container of a ball mill, where the in situ examination of the reaction mechanism is extremely challenging. As shown in this paper, useful indirect information can be obtained from detailed analysis of the reaction kinetics. A shaker mill with a single ball was used, so that time could be replaced with the number of collisions as the variable of kinetics. A simple stochastic model was developed that is capable of describing the kinetics of gradual mechanochemical reactions and the variation of physical properties such as grain size. The kinetic constant is directly related to the fraction of powder processed in a single collision, and its value indicates that only a few micrograms of powder are processed in a single collision. Measuring the kinetic constant as a function of impact energy revealed that a minimum impact energy, on the order of a few hundreds of a Joule, is needed to initiate chemical change. The model was also applied to the self-sustaining reaction between Ti and graphite. In that case, the critical number of collisions required for ignition characterizes the speed of mechanical activation.

Radiation reaction, the force experienced by an accelerated charge due to radiation emission, has long been the subject of extensive theoretical and experimental research. Experimental verification of a quantum, strong-field description of radiation reaction is fundamentally important, and has wide-ranging implications for astrophysics, laser-driven particle acceleration, next-generation particle colliders and inverse-Compton photon sources for medical and industrial applications. However, the difficulty of accessing regimes where strong field and quantum effects dominate inhibited previous efforts to observe quantum radiation reaction in charged particle dynamics with high significance. We report a high significance ( > 5 σ ) observation of strong-field radiation reaction on electron spectra where quantum effects are substantial. We obtain quantitative, strong evidence favouring the quantum-continuous and quantum-stochastic models over the classical model; the quantum models perform comparably. The lower electron energy losses predicted by the quantum models account for their improved performance. Model comparison was performed using a novel Bayesian framework, which has widespread utility for laser-particle collision experiments, including those utilising conventional accelerators, where some collision parameters cannot be measured directly. Radiation reaction (RR) on particles in strong fields is the subject of intense experimental research, but previous efforts lacked statistical significance due to the extreme regimes required. Here, the authors report a 5 σ observation of RR and obtain strong, quantitative evidence favouring quantum models over classical, using an all-optical setup where electrons are accelerated by a laser in a gas jet before colliding with a second, intense pulse.