Lattice Field Research Articles

Electrical Control of Magnetism through Proton Migration in Fe3O4/Graphene Heterostructure.

Ion migration has direct and crucial bearing on the crystal lattice field, electron filling, orbital occupation and spin polarization, which in turn changes the physical properties. Electric field is an effective way to control ion migration, but it may include simultaneous movement of multiple ions and increase the complexity of the system. Therefore, controllable and selective single ion migration with an unambiguous mechanism is highly desired. Here, the magnetic moments of Fe3O4 could be reversibly controlled by ionic liquid gating on the basis of migration of pure protons. A bilayer graphene could serve as an ion sieve, allowing only protons rather than oxygen ions or hydroxyl groups to participate in the gating process, thus guaranteeing the reversibility of magnetic property changes. This work is expected to supply an ideal arena for electrically sketching the functionalities of solid state materials based on the selective ion migration.

Tensor lattice field theory for renormalization and quantum computing

One goal in understanding quantum chromodynamics (QCD) includes solving how quarks and gluons combine to form the hadrons and nuclei seen in nature. With lattice QCD, progress has been made regarding the calculation of masses and couplings. However, the real-time evolution and the critical behavior at finite density of strong particles in colliders, stars, or after the big bang remain a challenging problem despite their potential to detect the existence of new physics. The tensor methods for lattice field theories provide a route to handle strongly correlated systems across different subfields using renormalization group methods or quantum computing.

Spacetime symmetric qubit regularization of the asymptotically free two-dimensional O(4) model

We explore if space-time symmetric lattice field theory models with a finite Hilbert space per lattice site can reproduce asymptotic freedom in the two-dimensional $O(4)$ model. We focus on a simple class of such models with a five dimensional local Hilbert space. We demonstrate how even the simplest model reproduces asymptotic freedom within the D-theory formalism but at the cost of increasing the size of the Hilbert space through coupling several layers of a two-dimensional lattice. We then argue that qubit regularization can be viewed as an effective field theory (EFT) even if the continuum limit cannot be reached, as long as we can tune the model close enough to the continuum limit where perturbation theory, or other analytical techniques, become viable. We construct a simple lattice model on a single layer with a four dimensional local Hilbert space that acts like an excellent EFT of the original theory.

Solution of the Thirring model in thimble regularization

Thimble regularisation of lattice field theories has been proposed as a solution to the infamous sign problem. It is conceptually very clean and powerful, but it is in practice limited by a potentially very serious issue: in general many thimbles can contribute to the computation of the functional integrals. Semiclassical arguments would suggest that the fundamental thimble could be sufficient to get the correct answer, but this hypothesis has been proven not to hold true in general. A first example of this failure has been put forward in the context of the Thirring model: the dominant thimble approximation is valid only in given regions of the parameter space of the theory. Since then a complete solution of this (simple) model in thimble regularisation has been missing. In this paper we show that a full solution (taking the continuum limit) is indeed possible. It is possible thanks to a method we recently proposed which de facto evades the need to simulate on many thimbles.

Quantum field theories, Markov random fields and machine learning

The transition to Euclidean space and the discretization of quantum field theories on spatial or space-time lattices opens up the opportunity to investigate probabilistic machine learning within quantum field theory. Here, we will discuss how discretized Euclidean field theories, such as the ϕ 4 lattice field theory on a square lattice, are mathematically equivalent to Markov fields, a notable class of probabilistic graphical models with applications in a variety of research areas, including machine learning. The results are established based on the Hammersley-Clifford theorem. We will then derive neural networks from quantum field theories and discuss applications pertinent to the minimization of the Kullback-Leibler divergence for the probability distribution of the ϕ 4 machine learning algorithms and other probability distributions.

XXXII IUPAP Conference on Computational Physics

Damien Foster1, Nikolaos G. Fytas1, Charo del Genio1, Ran Holtzman1, Abhishek Kumar1, Susanne Horn1, Alban Potherat1, Martin Weigel2, and Taras Yavors’kii1 1 Centre for Fluid and Complex Systems, Coventry University, Coventry CV1 5FB, United Kingdom 2 Institut für Physik, Technische Universität Chemnitz, 09107 Chemnitz, GermanyE-mail: martin.weigel@physik.tu-chemnitz.de The 32nd IUPAP Conference in Computational Physics was held online August 2-5, 2021 with organizational support from Coventry University. The Conference in Computational Physics series of meetings is held annually under the auspices of the International Union of Pure and Applied Physics (IUPAP) at international locations alternating typically between Europe, the Americas, and the Asian and Pacific regions. It covers all areas of the computational sciences with a relation to physical applications, making it the largest and leading recurrent international meeting in computational physics. Typical topics covered include statistical mechanics and complex systems, soft matter and biophysics, materials and nano-science, fluid dynamics, quantum manv-body physics, quantum computing, lattice field theory, astrophysics, gravitation and cosmology, novel hardware and software, computational physics education, machine learning and algorithms as well as geophysics and porous media. The format combines plenary overview lectures with a broad range of topical parallel sessions featuring invited impact talks as well as oral contributions and poster sessions, complemented by discussion sessions.The organisation of the 2020 meeting was given to the present group of organisers for a meeting to be held in physical presence in Coventry. It was planned for August 2020, but with the advent of the Coronavius pandemic it was decided in April 2020 to postpone the meeting to 2021 with the hope of holding it on site. We were quite confident back then that the meeting could be held face-to-face in 2021, but the virus proved to be more persistent than we had envisaged, such that CCP2021 was held entirely online. While this disappointed some, it also offered a number of opportunities to explore new forms of scientific and social interaction. We used a virtual conference centre constructed in Gather Town that included spaces for poster sessions and exhibition space for sponsors as well as many opportunities for formal and informal discussions among participants. All oral presentations were delivered on Zoom, with the vast majority of talks delivered live and a handful of pre-recorded videos. To support discussions revolving around the presentations, we also ran a discussion space on Slack with channels for each session and a common discussion forum. All oral presentations were recorded and made available to registered participants on the conference website at https://ccp2021.complexity-coventry.org.The conference featured 425 registrations, with 296 fully completed, coming from a wide range of countries, with the most represented being Japan, the United Kingdom, the United States of America, Germany, India, France, Russia and China. The program consisted of 15 plenary speakers, listed below, as well as 33 invited talks, 100 contributed talks and 72 poster contributions. The scientific sessions were complemented by cultural presentations as well as the award session for the IUPAP Young Scientist Prizes in Computational Physics which for 2020 and 2021 were awarded to Zhijun Wang and Prineha Narang, respectively. In total, these contributions led to a very exciting program, and the technical setup allowed for a rather interactive meeting. Although the actual experience might not quite have matched up to that of a traditional face-to-face conference, it was felt by many that this meeting format also has its upsides as it is more inclusive, more ecological, more diverse, and more family friendly that the traditional one.All authors of accepted contributions to the conference were invited to submit a full paper to the proceedings. These papers are collected in the present volume, covering all major areas represented at the conference and thus providing an excellent representation of where computational physics research stands today.We would like to thank all participants of the conference, all contributors to the scientific program and all authors of papers in this proceedings volume. Finally, we would like to acknowledge support for the conference by the IUPAP, the European Physical Society (EPS), the Institute of Physics (IOP), Coventry University, Technische Universität Chemnitz, the European Physical Journal (EPJ), Computation (MDPI), Entropy (MDPI), and MapleSoft.List of titles Local organising Committee, International advisory board, Program Committee, Plenary Speakers, Invited Speakers are available in this Pdf.

Stoichiometric dependence and laser heating effect on the luminescence thermometric performance of Er3+, Yb3+: YuGdwVO4 microparticles in the non-saturation regime

The performance of YuGdwVO4 microcrystals with different atomic concentrations of Y3+ and Gd3+ ions, co-doped Er3+-Yb3+, as thermometers, exploiting two different calculation methods based on the fluorescence intensity ratio is investigated in the non-saturation regime. At a low excitation power density of 20 W cm−2, the thermometric parameters are approximately the same for all the analyzed sensors. Whereas for an excitation power density of 155 W cm−2, they are widely different all along the 303–513 K temperature range of study. Such as an increase on the Gd3+ ion concentration in the microcrystals induces a lattice expansion that can result in the decreasing of the lattice field surrounding the Er3+ ions and then it could enhance greatly the thermometric performances. For both calculation methods, it has been demonstrated that the ∆EFIR (fitted from the FIR curves) and the ∆ETS (determined using the TeSen Calculator program) values are lower than the ∆E` experimental (fitted from the emission spectra measured at room temperature), whenever the sample is heated and then the thermometric parameters are less competitive.

Tailoring polarization singularity lattices by phase engineering of three-beam interference

Structured optical lattices obtained from interference of three linearly polarized plane waves arranged in a cone geometry produce interlaced polarization singularity structures. These lattices are known to be populated with both C-point and V-point singularities. All the lattice fields abide by the principle of index conservation. In this article, we focused on tailoring these polarization singularity lattices by perturbing the interfering beams with a relative encoded phase. We have shown that a spatial lateral-shifting of the ellipse- and vector field singularities by an order of lattice parameter can be achieved through an appropriate phase engineered design. Similar phase engineering in six and eight beam interference method of lattice generation produces different results. In six and eight beam interference, phase engineering enables realization of C-point only lattices and provides handedness control for the ellipse field singularities, whereas in three beam interference case, there is only a translation shift in the lattice structure.

Qubit Regularization and Qubit Embedding Algebras

Qubit regularization is a procedure to regularize the infinite dimensional local Hilbert space of bosonic fields to a finite dimensional one, which is a crucial step when trying to simulate lattice quantum field theories on a quantum computer. When the qubit-regularized lattice quantum fields preserve important symmetries of the original theory, qubit regularization naturally enforces certain algebraic structures on these quantum fields. We introduce the concept of qubit embedding algebras (QEAs) to characterize this algebraic structure associated with a qubit regularization scheme. We show a systematic procedure to derive QEAs for the O(N) lattice spin models and the SU(N) lattice gauge theories. While some of the QEAs we find were discovered earlier in the context of the D-theory approach, our method shows that QEAs are far richer. A more complete understanding of the QEAs could be helpful in recovering the fixed points of the desired quantum field theories.

Regularization of the complex Langevin method

The complex Langevin method, a numerical method used to compute the ensemble average with a complex partition function, often suffers from runaway instability. We study the regularization of the complex Langevin method via augmenting the action with a stabilization term. Since the regularization introduces biases to the numerical result, two approaches, named 2R and 3R methods, are introduced to recover the unbiased result. The 2R method supplements the regularization with regression to estimate the unregularized ensemble average, and the 3R method reduces the computational cost by coupling the regularization with a reweighting strategy before regression. Both methods can be generalized to the SU(n) theory and are assessed from several perspectives. Several numerical experiments in the lattice field theory are carried out to show the effectiveness of our approaches.

Strain and pseudo-magnetic fields in optical lattices from density-assisted tunneling

Applying time-periodic modulations is routinely used to control and design synthetic matter in quantum-engineered settings. In lattice systems, this approach is explored to engineer band structures with non-trivial topological properties, but also to generate exotic interaction processes. A prime example is density-assisted tunneling, by which the hopping amplitude of a particle between neighboring sites explicitly depends on their respective occupations. Here, we show how density-assisted tunneling can be tailored in view of simulating the effects of strain in synthetic graphene-type systems. Specifically, we consider a mixture of two atomic species on a honeycomb optical lattice: one species forms a Bose-Einstein condensate in an anisotropic harmonic trap, whose inhomogeneous density profile induces an effective uniaxial strain for the second species through density-assisted tunneling processes. In direct analogy with strained graphene, the second species experiences a pseudo-magnetic field, hence exhibiting relativistic Landau levels and the valley Hall effect. Our proposed scheme introduces a unique platform for the investigation of strain-induced gauge fields, opening the door to future studies of their possible interplay with quantum fluctuations and collective excitations.

Large-[formula omitted] Chern insulators: Lattice field theory and quantum simulation approaches to correlation effects in the quantum anomalous Hall effect

Four-Fermi quantum field theories in (2+1) dimensions lie among the simplest models in high-energy physics, the understanding of which requires a non-perturbative lattice formulation addressing their strongly-coupled fixed points. These lattice models are also relevant in condensed matter, as they offer a neat playground to explore strong correlations in the quantum anomalous Hall (QAH) effect. We give a detailed description of our multidisciplinary approach to understand the fate of the QAH phases as the four-Fermi interactions are increased, which combines strong-coupling and effective-potential techniques, unveiling a rich phase diagram with large-N Chern insulators and Lorentz-breaking fermion condensates. Moreover, this toolbox can be enlarged with recent advances in quantum information science, as we show that tensor-network algorithms based on projected entangled pairs can be used to improve our understanding of the strong-coupling limit. We also present a detailed scheme that uses ultra-cold atoms in optical lattices with synthetic spin–orbit coupling to build quantum simulators of these four-Fermi models. This yields a promising alternative to characterize the strongly-coupled fixed points and, moreover, could also explore real-time dynamics and finite-fermion densities.

Extraordinary anisotropic magnetoresistance in CaMnO3/CaIrO3 heterostructures

The realization of fourfold anisotropic magnetoresistance (AMR) in $3d\ensuremath{-}5d$ heterostructures has boosted major efforts in antiferromagnetic (AFM) spintronics. However, despite the potential of incorporating strong spin-orbit coupling, only small AMR signals have been detected thus far, prompting a search for mechanisms to enhance the signal. In this paper, we demonstrate an extraordinarily elevated fourfold AMR of 70% realized in $\mathrm{CaMn}{\mathrm{O}}_{3}/\mathrm{CaIr}{\mathrm{O}}_{3}$ thin film superlattices. We find that the biaxial magnetic anisotropy and the spin-flop transition in a nearly Mott insulating phase form a potent combination, each contributing one order of magnitude to the total signal. Dynamics between these phenomena capture a subtle interaction of pseudospin coupling with the lattice and external magnetic field, an emergent phenomenon creating opportunities to harness its potential in AFM spintronics.

Electronic defects in lattices of YBa2Cu3O7 and La2 − xSrxCuO4

Using emission Mössbauer spectroscopy data for the 67Zn isotope and nuclear quadrupole resonance data for the 17O isotope, as well as calculations of the lattice electric field gradient, the effective charges of all atoms in superconducting copper metal oxide YBa2Cu3O7 and La2 – xSrxCuO4 crystal lattices were determined. The effective charges of metal atoms and most oxygen atoms correspond to their standard oxidation states (Y3+, La3+, Ba2+, Sr2+, Cu2+ and O2−). However, the atoms of chain oxygen (in YBa2Cu3O7) and planar oxygen (in YBa2Cu3O7 and La2 – xSrxCuO4) show a reduced charge, which is explained by the localisation of holes in the corresponding sublattices.

Progress applying density of states for gravitational waves

Many models of composite dark matter feature a first-order confinement transition in the early Universe, which would produce a stochastic background of gravitational waves that will be searched for by future gravitationalwave observatories. We present work in progress using lattice field theory to predict the properties of such first-order transitions. Targeting SU(N) Yang– Mills theories, this work employs the Logarithmic Linear Relaxation (LLR) density of states algorithm to avoid super-critical slowing down at the transition.

Is the Universe Actually Holographic?

In this letter, we are going to reexamine the holographic dark energy concept that is proposed for cosmological applications. By considering precisely the bounds on the entropy arisen from lattice field theory on one side and Bekenstein-Hawking entropy of black holes on another side, it is shown that the so-called holographic dark energy can not be mimicked as easily as claimed in the literature. In addition, the limits which are discussed in the literature on the electron $(g-2)$ experiments, are rediscussed here. It is shown that the corrections to the electron magnetic momentum should be of the order of ${O}(10^{-23})$

Computing Lattice Field Theory by Tensor Networks―Challenge to Sign Problem

Computing Lattice Field Theory by Tensor Networks―Challenge to Sign Problem

Cold atoms meet lattice gauge theory

The central idea of this review is to consider quantum field theory models relevant for particle physics and replace the fermionic matter in these models by a bosonic one. This is mostly motivated by the fact that bosons are more ‘accessible’ and easier to manipulate for experimentalists, but this ‘substitution’ also leads to new physics and novel phenomena. It allows us to gain new information about among other things confinement and the dynamics of the deconfinement transition. We will thus consider bosons in dynamical lattices corresponding to the bosonic Schwinger or Bose–Hubbard models. Another central idea of this review concerns atomic simulators of paradigmatic models of particle physics theory such as the Creutz–Hubbard ladder, or Gross–Neveu–Wilson and Wilson–Hubbard models. This article is not a general review of the rapidly growing field—it reviews activities related to quantum simulations for lattice field theories performed by the Quantum Optics Theory group at ICFO and their collaborators from 19 institutions all over the world. Finally, we will briefly describe our efforts to design experimentally friendly simulators of these and other models relevant for particle physics.This article is part of the theme issue ‘Quantum technologies in particle physics’.

Flow-based sampling for fermionic lattice field theories

Algorithms based on normalizing flows are emerging as promising machine learning approaches to sampling complicated probability distributions in a way that can be made asymptotically exact. In the context of lattice field theory, proof-of-principle studies have demonstrated the effectiveness of this approach for scalar theories, gauge theories, and statistical systems. This work develops approaches that enable flow-based sampling of theories with dynamical fermions, which is necessary for the technique to be applied to lattice field theory studies of the Standard Model of particle physics and many condensed matter systems. As a practical demonstration, these methods are applied to the sampling of field configurations for a two-dimensional theory of massless staggered fermions coupled to a scalar field via a Yukawa interaction.

Plasmonic metasurfaces manipulating the two spin components from spin–orbit interactions of light with lattice field generations

Abstract Artificial nanostructures in metasurfaces induce strong spin–orbit interactions (SOIs), by which incident circularly polarized light can be transformed into two opposite spin components. The component with an opposite helicity to the incident light acquires a geometric phase and is used to realize the versatile functions of the metasurfaces; however, the other component, with an identical helicity, is often neglected as a diffused background. Here, by simultaneously manipulating the two spin components originating from the SOI in plasmonic metasurfaces, independent wavefields in the primary and converted spin channels are achieved; the wavefield in the primary channel is controlled by tailoring the dynamic phase, and that in the converted channel is regulated by designing the Pancharatnam–Berry phase in concurrence with the dynamic phase. The scheme is realized by generating optical lattice fields with different topologies in two spin channels, with the metasurfaces composed of metal nanoslits within six round-apertures mimicking the multi-beam interference. This study demonstrates independent optical fields in a dual-spin channel based on the SOI effect in the metasurface, which provides a higher polarization degree of freedom to modify optical properties at the subwavelength scale.