Article
Chemistry, Multidisciplinary
Leon Otis, Eric Neuscamman
Summary: We discuss recent progress in excited-state-specific quantum chemistry and quantum Monte Carlo and show how combining methods from these fields can predict excited states accurately. Important advances in both fields include improved optimization methods, handling of complicated wave function forms, and balancing the quality of wave functions for ground and excited states. Demonstrations using a combination of specific quantum chemistry and variational Monte Carlo show that this approach is more reliable and accurate than other high-level methods and can provide clarity in cases where existing methods do not agree.
WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE
(2023)
Article
Optics
Renato Pessoa, S. A. Vitiello, L. A. Pena Ardila
Summary: The properties of polarons in an ultracold Fermi gas were studied using Quantum Monte Carlo techniques and both zero-range and square-well potential models. The polaron effective mass, binding energy, and effective coupling were computed, with the latter obtained using Landau-Pomeranchuk's weakly interacting quasiparticle model. The contact parameter was estimated by fitting the pair distribution function of atoms in different spin states.
Article
Materials Science, Multidisciplinary
Massimo Boninsegni
Summary: The bound state of a He-3 atom at the interface between crystalline and superfluid phases of He-4 is investigated using first principle Quantum Monte Carlo simulations. The results show that the He-3 atom is sharply localized in a quasi-2D layer of He-4, located in the intermediate region between the solid and liquid states. The localization and quantum-mechanical exchanges of the He-3 atom are influenced by the attractive strength of the substrate.
RESULTS IN PHYSICS
(2022)
Article
Chemistry, Physical
Tina N. Mihm, William Z. Van Benschoten, James J. Shepherd
Summary: A new approach using low-cost calculations was developed to find a twist angle that matches the coupled cluster doubles energy in a finite unit cell. The method was shown to have comparable accuracy with exact methods beyond coupled cluster doubles theory. Additionally, for small system sizes, the same twist angle can be found by comparing energies directly, suggesting a potential route towards twist angle selection.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Materials Science, Multidisciplinary
Massimo Boninsegni, Saverio Moroni
Summary: The second layer of 4He adsorbed on a graphite substrate is studied using Quantum Monte Carlo simulations. The substrate's corrugation is fully taken into account in a microscopic model, and the results are compared to those obtained with a smooth substrate. The main effect of the corrugation is a 20% reduction in the superfluid fraction of the top layer at zero temperature. No evidence of any commensurate (7/12) crystalline and/or supersolid phase is found, and the superfluid transition temperature is estimated to be -0.75 K. The implications of these findings on recent experiments are discussed.
RESULTS IN PHYSICS
(2023)
Article
Physics, Applied
Massimo Boninsegni
Summary: First-principle computer simulations show no evidence of a liquid top layer or proximity to a superfluid transition in a thin parahydrogen film adsorbed on a silica substrate at low temperatures, contradicting recent experimental claims. The top layer is found to be an insulating crystal without quantum-mechanical exchanges between molecules, consistent with observations on other substrates.
JOURNAL OF LOW TEMPERATURE PHYSICS
(2021)
Article
Physics, Multidisciplinary
Matteo Ciardi, Tommaso Macri, Fabio Cinti
Summary: This work explores methodology for investigating interacting systems with contact interactions, introducing a class of zonal estimators for path-integral Monte Carlo methods aimed at providing physical information about limited regions of inhomogeneous systems. The usefulness of zonal estimators is demonstrated through their application to a system of trapped bosons in a quasiperiodic potential in two dimensions, focusing on finite temperature properties across a wide range of potential values. Finally, the generalization of such estimators to local fluctuations of particle numbers and magnetic ordering in multi-component systems, spin systems, and systems with nonlocal interactions is discussed.
Article
Chemistry, Physical
Oliver A. Bramley, Timothy J. H. Hele, Dmitrii Shalashilin
Summary: Zombie states are a formalism that describes coupled coherent fermionic states in a computationally tractable manner. This study extends the previous work on Zombie states and develops efficient algorithms for evaluating operators and addressing normalization. It also presents techniques for improving accuracy and calculating low-lying excited states.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Abdallah Ammar, Anthony Scemama, Emmanuel Giner
Summary: In this study, popular SCI algorithms were extended to the TC framework, showcasing the importance of considering non-Hermitian character for fast convergence of TC energy, the significant impact of left-function quality on results, and the faster convergence of SCI expansion in TC framework compared to traditional SCI in terms of basis set and Slater determinant number.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Jonas Feldt, Antoine Bienvenu, Roland Assaraf
Summary: In this paper, a new estimator in the variational Monte Carlo framework is proposed, which utilizes numerically cheap single-core subsamplings to improve the estimation of molecular properties. Furthermore, a spin-dependent core definition is introduced to simplify the algorithm and enhance its efficiency.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Giovani L. Rech, Andre L. Martinotto, Janete E. Zorzi, Claudio A. Perottoni
Summary: The relative stability between the crystal structure of alpha-F-2, space group C2/c, and a hypothesized high-pressure phase, space group Cmce, was investigated using Density Functional Theory and Quantum Monte Carlo calculations. The analysis of the phonon dispersion spectra showed that the Cmce phase exhibits dynamical instability near the Gamma-point at ambient pressure, which disappears under increasing pressure. This instability is attributed to the absence of sigma-holes in the fluorine molecule, resulting in repulsive head-to-head interactions between molecules.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2023)
Article
Physics, Multidisciplinary
Kaisei Ooe, Akimitsu Miyamae, Kenichi Asano
Summary: We simulate the formation of polyexcitons in 2D systems of electrons and holes and find that the energy to extract one exciton from the n-exciton bound states grows linearly with the exciton number, n, regardless of the interplanar distance, indicating the energetic binding of all pairs of excitons inside the polyexciton by chemical bonds.
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN
(2023)
Article
Materials Science, Multidisciplinary
Yuichi Motoyama, Kazuyoshi Yoshimi, Junya Otsuki
Summary: Analytic continuation from the imaginary-time Green's function to the spectral function is crucial for studying the dynamical properties of quantum many-body systems. However, this process is unstable and has advantages and disadvantages. Combining SpM AC with Pade approximation in the SpM-Pade method can provide more accurate and stable results.
Article
Management
Joseph L. Breeden, Yevgeniya Leonova
Summary: This article develops a Monte Carlo method that estimates the loss distribution for a single loan, allowing for a better understanding of the risk distribution due to modelling and macroeconomic uncertainty. The study finds that the Monte Carlo simulation results fit well with a Lognormal distribution. Additionally, the feasibility of using quantum computers for the calculations is explored, showing potential for significant speed enhancement, albeit with the need for further quantum algorithm development for the full analysis of competing risks.
JOURNAL OF THE OPERATIONAL RESEARCH SOCIETY
(2023)
Article
Physics, Applied
Phong H. Nguyen, Massimo Boninsegni
Summary: The phase diagram of lattice hard core bosons with independently varying nearest-neighbor interactions along different crystallographic directions is studied using quantum Monte Carlo simulations. The results show the existence of a superfluid phase and two crystalline phases at half filling, either checkerboard or striped, while no supersolid phase is observed.
JOURNAL OF LOW TEMPERATURE PHYSICS
(2022)
Article
Physics, Multidisciplinary
Anatoly B. Kuklov, Lode Pollet, Nikolay Prokof'ev, Boris Svistunov
Summary: The study discusses the unique superflow effect observed in solid 4He, attributing it to the quasi-one dimensional superfluidity along the dislocation cores and thermal fluctuations of the dislocation shape.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Applied
Massimo Boninsegni
Summary: This study investigates the possible bound states of He-3 atoms near a weakly attractive substrate coated with a thin superfluid He-4 film using first principle computer simulations. The results show no evidence of such bound states, as the He-3 atoms always bind to the free He-4 surface, regardless of the thickness of the He-4 film.
JOURNAL OF LOW TEMPERATURE PHYSICS
(2023)
Article
Physics, Multidisciplinary
Hao Song, Janik Schoenmeier-Kromer, Ke Liu, Oscar Viyuela, Lode Pollet, M. A. Martin-Delgado
Summary: Fracton models provide novel gapped quantum phases that host immobile excitations and are beyond topological order. Optimal error thresholds for quantum error correcting codes based on fracton models are calculated, and higher thresholds are found compared to traditional topological codes. This highlights the potential of fracton phases as quantum memory platforms.
PHYSICAL REVIEW LETTERS
(2022)
Article
Chemistry, Multidisciplinary
Jieru Hu, Massimo Boninsegni
Summary: Equilibrium physical properties of solid and liquid parahydrogen were compared using first principle computer simulations for different intermolecular potentials. The most recent ab initio potential (Patkowski et al., J. Chem. Phys., 2008, 129, 094304) showed better agreement with experimental measurements for structural quantities, but may overestimate the kinetic energy per molecule by up to 10%. Overall, the comparison suggests that the potential of Patkowski et al. may be a better choice for simulating condensed phases of parahydrogen at moderate pressure.
APPLIED SCIENCES-BASEL
(2023)
Article
Materials Science, Multidisciplinary
Massimo Boninsegni, Saverio Moroni
Summary: The second layer of 4He adsorbed on a graphite substrate is studied using Quantum Monte Carlo simulations. The substrate's corrugation is fully taken into account in a microscopic model, and the results are compared to those obtained with a smooth substrate. The main effect of the corrugation is a 20% reduction in the superfluid fraction of the top layer at zero temperature. No evidence of any commensurate (7/12) crystalline and/or supersolid phase is found, and the superfluid transition temperature is estimated to be -0.75 K. The implications of these findings on recent experiments are discussed.
RESULTS IN PHYSICS
(2023)
Article
Physics, Multidisciplinary
Chao Zhang, Barbara Capogrosso-Sansone, Massimo Boninsegni, Nikolay V. Prokofev, Boris V. Svistunov
Summary: We present results of numerically exact simulations of the Bose one-component plasma, i.e., a Bose gas with pairwise Coulomb interactions among particles and a uniform neutralizing background. We compute the superconducting transition temperature for a wide range of densities, in two and three dimensions, for both continuous and lattice versions of the model. The Coulomb potential causes the weakly interacting limit to be approached at high density, but gives rise to no qualitatively different behavior, vis-à-vis the superfluid transition, with respect to short-ranged interactions. Our results are of direct relevance to quantitative studies of bipolaron mechanisms of (high-temperature) superconductivity.
PHYSICAL REVIEW LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Domenico Giuliano, Phong H. Nguyen, Andrea Nava, Massimo Boninsegni
Summary: We present a theoretical study on the Berezinskii-Kosterlitz-Thouless transition in a two-dimensional superfluid with an externally imposed density modulation. Using analytical and numerical techniques, we show that as the modulation amplitude increases, the system exhibits behavior similar to the anisotropic x-y model, with a lower superfluid transition temperature and anisotropic response, but no dimensional crossover.
Article
Physics, Multidisciplinary
Henning Schloemer, Annabelle Bohrdt, Lode Pollet, Ulrich Schollwoeck, Fabian Grusdt
Summary: This study uses the density matrix renormalization group method at finite temperature to analyze the formation of stripes in the mixed-dimensional t-J model. It is found that a stable vertical stripe phase can be formed in the absence of pairing, exhibiting incommensurate magnetic order and long-range charge density wave profiles. The proposed model can be seen as a parent Hamiltonian of the stripe phase, and its hidden spin correlations contribute to the predicted resilience against quantum and thermal fluctuations.
PHYSICAL REVIEW RESEARCH
(2023)
Article
Physics, Multidisciplinary
Rajah P. Nutakki, Richard Roess-Ohlenroth, Dirk Volkmer, Anton Jesche, Hans-Albrecht Krug von Nidda, Alexander A. Tsirlin, Philipp Gegenwart, Lode Pollet, Ludovic D. C. Jaubert
Summary: Geometric frustration prevents magnetic systems from ordering, allowing for unconventional phases of matter. Using molecular design, we have created a material [Mn(II)(ta)2] that exhibits a centered pyrochlore lattice of Mn spins, which shows features of a classical spin liquid. Despite having a Curie-Weiss temperature of -21 K, the material only orders at 430 mK, making it a highly frustrated magnet.
PHYSICAL REVIEW RESEARCH
(2023)
Article
Materials Science, Multidisciplinary
T. R. Prisk, R. T. Azuah, D. L. Abernathy, G. E. Granroth, T. E. Sherline, P. E. Sokol, J. Hu, M. Boninsegni
Summary: We conducted an inelastic neutron scattering study of liquid and solid hydrogen using the wide Angular Range Chopper Spectrometer at Oak Ridge National Laboratory. Our findings show that the molecular mean-squared displacement increases with temperature near the liquid-solid phase transition, indicating the importance of thermal and quantum effects. Additionally, we observed a significant drop in kinetic energy upon melting of the crystals, which can be explained by the large increase in molar volume and Heisenberg indeterminacy principle. The results were compared with quantum Monte Carlo simulations based on different model potentials, and good agreement was found with the Silvera-Goldman and Buck potentials.
Article
Materials Science, Multidisciplinary
Giovanni Canossa, Lode Pollet, Ke Liu
Summary: This article investigates two specific cases of phase transitions that break subsystem symmetries. The models in question are two classical compass models with line-flip and plane-flip symmetries, which correspond to special limits of a Heisenberg-Kitaev Hamiltonian on a cubic lattice. The study shows that these models undergo a hybrid symmetry breaking, wherein the system exhibits distinct symmetry broken patterns in different submanifolds. For example, the system may appear magnetic within a chain or plane, but nematic-like when observed from a higher dimensionality. By using a set of subdimensional order parameters, the symmetry-broken phases are fully characterized, and numerical analysis confirms that both cases undergo a non-standard first-order phase transition. These findings provide new insights into phase transitions involving subsystem symmetries and generalize the concept of conventional spontaneous symmetry breaking.
Article
Materials Science, Multidisciplinary
Janik Schoenmeier-Kromer, Lode Pollet
Summary: We investigate the phase diagram of a one-dimensional Bose-Fermi-Hubbard model with scalar bosons at unit filling and S=1/2 fermions at half filling using quantum Monte Carlo simulations. The fermion-fermion interaction is set to zero. The main focus of our study is to understand the induced interactions between the fermions by the bosons, both for weak and strong interspecies coupling. We find that these induced interactions can result in competing instabilities favoring phase separation, superconducting phases, and density wave structures, often occurring on length scales of more than 100 sites. Additionally, we observe marginal bosonic superfluids with faster decay of the density matrix compared to pure bosonic systems with on-site interactions.
Article
Physics, Multidisciplinary
Nicolas Sadoune, Giuliano Giudici, Ke Liu, Lode Pollet
Summary: Experimental progress in qubit manufacturing requires new theoretical tools for quantum data analysis. This study demonstrates how unsupervised machine learning can analyze data from short-range entangled many-qubit systems. The method successfully constructs the phase diagram and identifies order parameters for different phases, including string order parameters. Furthermore, it can identify the explicit forms of stabilizers in the toric code under external magnetic fields. No prior information about the underlying Hamiltonian or quantum states is needed, as the machine outputs characteristic observables.
PHYSICAL REVIEW RESEARCH
(2023)
Article
Materials Science, Multidisciplinary
Julius Dicke, Lukas Rammelmueller, Fabian Grusdt, Lode Pollet
Summary: We investigate the phase diagram of two different mixed-dimensional t-Jz-J1 models on the square lattice, with hopping amplitude t only nonzero along the x direction. In the first bosonic model, the spin-exchange amplitude J1 is negative and isotropic along the x and y directions, with isotropic and positive Jz. The low-energy physics is characterized by spin-charge separation. In the second model, J1 is restricted to the x axis while Jz remains isotropic and positive. The model exhibits stripe patterns with antiferromagnetic Neel order at low temperature and high hole densities.
Article
Materials Science, Multidisciplinary
Andrea Nava, Domenico Giuliano, Phong H. Nguyen, Massimo Boninsegni
Summary: This study investigates the low temperature structural and superfluid properties of 4He confined in cylindrical nanopores using quantum Monte Carlo simulations. The results show that when the pore length greatly exceeds its radius, the 4He fluid displays remarkably one-dimensional behavior without dimensional crossover, contrary to recent claims by other authors. This system could potentially provide a viable pathway for the experimental observation of exotic behaviors, such as the junctions of interacting Tomonaga-Luttinger liquids, in a suitably designed network of nanopores.
