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In this contribution, we employ a recurrent neural network (RNN) architecture in a variational optimization to obtain the ground state of linear chains of planar, dipolar rotors. We test different local basis sets and discuss their impact on the sign structure of the many-body ground state wavefunction. It is demonstrated that the RNN ansatz we employ is able to treat systems with and without a sign problem in the ground state. For larger chains with up to 50 rotors, accurate properties, such as correlation functions and Binder parameters, are calculated. By employing quantum annealing, we show that precise entanglement properties can be obtained. All these properties allow one to identify a quantum phase transition between a paraelectric and a ferroelectric quantum phase. [ABSTRACT FROM AUTHOR]

The theoretical modeling of high-pressure ice remains challenging owing to the complexity in accurately reflecting its properties attributable to nuclear quantum effects. To explore the nuclear quantum effects of the phase transition between Ice VII and Ice X, we introduce an approach based on ab initio path-integral molecular dynamics. The results indicate that quantum effects facilitate the phase transition, with the observed isotope effects consistent with the experimental outcomes. We demonstrate that quantum effects manifest differently across ice phases: In Ice VII, quantum effects reduce the pressure through the centralization of protons. In contrast, in Ice X, quantum effects increase the pressure owing to the increased kinetic energy of zero-point vibration. [ABSTRACT FROM AUTHOR]

We present a comprehensive investigation into the dissociative chemisorption of HOD on a rigid Ni(100) surface using an approximate full-dimensional (9D) quantum dynamics approach, which was based on the time-dependent wave-packet calculations on a full-dimensional potential energy surface obtained through neural network fitting to density functional theory energy points. The approximate-9D probabilities were computed by averaging the seven-dimensional (7D) site-specific dissociation probabilities across six impact sites with appropriate relative weights. Our results uncover a distinctive bond-selective effect, demonstrating that the vibrational excitation of a specific bond substantially enhances the cleavage of that excited bond. The product branching ratios are substantially influenced by which bond undergoes excitation, exhibiting a clear preference for the product formed through the cleavage of the excited bond over the alternative product. [ABSTRACT FROM AUTHOR]

In this work, we perform a density matrix renormalization group study of chains of planar rotors interacting via dipolar interactions. By exploring the ground state from weakly to strongly interacting rotors, we find the occurrence of a quantum phase transition between a disordered and a dipole-ordered quantum state. We show that the nature of the ordered state changes from ferroelectric to antiferroelectric when the relative orientation of the rotor planes varies and that this change requires no modification of the overall symmetry. The observed quantum phase transitions are characterized by critical exponents and central charges, which reveal different universality classes ranging from that of the (1 + 1)D Ising model to the 2D classical XY model. [ABSTRACT FROM AUTHOR]

With the development of electronic structure theory, a new class of materials—quantum ones—has been recognized by the community. Traditionally, it has been believed that the properties of such compounds cannot be described within the framework of modern density functional theory, and indeed, more advanced post-mean-field theory methods are needed. Motivated by this, herein, we develop a fundamental understanding of such complex materials using the example of paramagnetic YNiO3, which is experimentally known to exhibit metal-to-insulator phase transition. We show that this material has a temperature-dependent distribution of local motifs. Thus, while at low temperatures, YNiO3 has distinct structural disproportionation with the formation of large and small octahedra, as the temperature increases, this disproportionation is suppressed. We also explain the paramagnetic monoclinic to paramagnetic orthorhombic phase transition within the double-well to single-well energy profile, predicting the variation in the corresponding energy profile as a function of octahedral size distribution. In this way, we demonstrate a fundamental understanding of structural phase transitions in quantum materials, giving insights into how they can be used for different applications and what minimum level of theory is needed to describe such types of complex materials at finite temperatures. [ABSTRACT FROM AUTHOR]

The semiconductor quantum well based on mercury telluride is characterized by two distinct phases: conventional insulating phase and topological insulating phase with helical edge states. The system undergoes a topological quantum phase transition from one phase to the other, tuned by the critical geometric parameters of the quantum well. It is shown that the quantum states in each phase exhibit distinct flavors of Bloch oscillations, depending strongly on the geometric parameters and crystal momentum of the system. In particular, the group and Berry velocities and the real-space trajectories exhibit pronounced Bloch oscillations. Interestingly, the x - and y -components of the group velocity are interchanged by interchanging their corresponding components of the crystal momentum. In addition, a Gaussian wave packet undergoes distinct time evolution in each quantum phase of the HgTe quantum well. Moreover, the effects of applied in-plane electric and transverse magnetic fields are determined within the framework of Newtonian mechanics, leading to the geometric visualization of such an oscillatory motion. We find that in the presence of both applied in-plane electric and transverse magnetic fields simultaneously, the system undergoes a dynamic phase transition between confined and de-confined states, tuned by the relative strength of the fields. It is argued that the distinct Bloch oscillations originate from the peculiar band structure of HgTe quantum wells in each quantum phase. Furthermore, we find that the direct-current drift velocity in each quantum phase exhibits negative differential conductivity, a hallmark of the Bloch oscillation regime. [ABSTRACT FROM AUTHOR]

Considerable evidence supports the existence of many-body localization (MBL) phase transitions, although accurately determining the critical disorder intensity remains challenging due to significant instabilities in system size within the examined parameters. In this study, we employ the global quantum discord (GQD) to investigate MBL phase transitions and identify the critical points of the quantum Ising spin chain subjected to both disordered interacting and disordered external fields. Our analysis of GQD demonstrates its effectiveness in identifying the critical points between the thermal and the MBL phases. We further utilize the temporal evolution of GQD to comprehensively explore the characteristics of MBL phase transitions in the disordered quantum Ising spin chain. Our findings suggest that MBL phase transitions adhere to the same generality category based on the scaling analysis. Additionally, we investigate the effects of these examined parameters on the GQD and its dynamics and use them to estimate the critical points. [ABSTRACT FROM AUTHOR]

Cation deficiency tuning is a central issue in thin‐film epitaxy of functional metal oxides, as it is typically more difficult than anion deficiency tuning, as anions can be readily supplied from gas sources. Here, highly effective internal deficiency compensation of Ru cations is demonstrated for Ca2RuO4 epitaxial films based on diffusive transfer of metal cations in the A2BO4 Ruddlesden–Popper lattice from solid‐phase cation sources. Through detailed structural characterization of Ca2RuO4/LaAlO3 (001) thin films grown with external cation sources by solid‐phase epitaxy, the occurrence of intercalation‐like, interstitial diffusion of La cations (from the substrates) in the A2BO4 structure is revealed, and that of Ru cations is also suggested. Relying on the interstitial‐type diffusion, an optimized Ru deficiency compensation method, which does not induce the formation of Can+1RunO3n+1 Ruddlesden–Popper impurity phases with higher n, is proposed for Ca2RuO4 epitaxial films. In the Ca2RuO4/LaAlO3 (001) thin films grown with Ru deficiency compensation, record‐high resistivity values (102–10−1 Ω cm) and a large (more than 200 K) increase in the temperature range of the nonlinear transport properties are demonstrated by transport measurements, demonstrating the possible advantages of this method in the control of the current‐induced quantum phase transition of Ca2RuO4. [ABSTRACT FROM AUTHOR]

The xene family of topological insulators plays a key role in many proposals for topological electronic, spintronic, and valleytronic devices. These proposals rely on applying local perturbations, including electric fields and proximity magnetism, to induce topological phase transitions in xenes. However, these techniques lack control over the geometry of interfaces between topological regions, a critical aspect of engineering topological devices. We propose adatom decoration as a method for engineering atomically precise topological edge modes in xenes. Our first-principles calculations show that decorating stanene with Zn adatoms exclusively on one of two sublattices induces a topological phase transition from the quantum spin Hall (QSH) to quantum valley Hall (QVH) phase and confirm the existence of spin-valley polarized edge modes propagating at QSH/QVH interfaces. We conclude by discussing technological applications of these edge modes that are enabled by the atomic precision afforded by recent advances in adatom manipulation technology. The authors propose sublattice-selective decoration by Zn adatoms as a method to engineer precise topological edge modes in xenes. First-principles calculations on Zn decorated stanene reveal a quantum spin Hall (QSH) to quantum valley Hall (QVH) transition and spin-valley polarized modes propagating at the QSH/QVH interface. [ABSTRACT FROM AUTHOR]

The mutual information method has demonstrated to be very useful for deriving the potential order parameter of a system. Although the method suggests some constraints which help to define this quantity, there is still some freedom in the definition. The method then results inefficient for cases where we have order parameters with a large number of constants in the expansion, which happens when we have many degenerate vacuums. Here, we introduce some additional constraints based on the existence of broken symmetries, which help us to reduce the arbitrariness in the definitions of the order parameter in the proposed mutual information method. [ABSTRACT FROM AUTHOR]

Including the previously ignored dispersion of phonons we revisit the metal-insulator transition problem in one-dimensional electron-phonon systems on the basis of a modified spinless fermion Holstein model. Using matrix-product-state techniques we determine the global ground-state phase diagram in the thermodynamic limit for the half-filled band case, and show that in particular the curvature of the bare phonon band has a significant effect, not only on the transport properties characterized by the conductance and the Luttinger liquid parameter, but also on the phase space structure of the model as a whole. While a downward curved (convex) dispersion of the phonons only shifts the Tomonaga-Luttinger-liquid to charge-density-wave quantum phase transition towards stronger EP coupling, an upward curved (concave) phonon band leads to a new phase-separated state which, in the case of strong dispersion, can even completely cover the charge-density wave. Such phase separation does not occur in the related Edwards fermion-boson model. [ABSTRACT FROM AUTHOR]

We study the dynamics of a single spin coupled to a bosonic bath at zero temperature driven by a ramp of the bias field. A single spin coupled to a bosonic sub-Ohmic bath exhibits a quantum phase transition at a certain strength of spin-boson coupling. When the bias field is ramped from a large value to zero at this critical coupling strength, the system initialized at the ground state ends up with a finite magnetization due to the critical slowing down near the transition. On the basis of the pulse-impulse approximation, we derive a scaling law between the residual magnetization and the ramp speed. The obtained scaling relation is examined using a numerical simulation based on the tensor network. The data are in favor of the scaling law to hold. We discuss the demonstration of our theoretical results by means of quantum simulation using the quantum annealer. [ABSTRACT FROM AUTHOR]

The quantum injectivity problem classifies frames which are injective with respect to self-adjoint Hilbert-Schmidt operators. In this paper, we aim to analyze quantum injective frames in terms of the excess of frame elements in R n . Especially, we investigate the connection between the injectivity, full spark and phase retrieval frames. In addition, we detect injective (alternate) dual frames and show that the family of quantum injective dual frames is open and dense in the set of all dual frames. Finally, the stability of quantum injective frames will be addressed. [ABSTRACT FROM AUTHOR]

Context: In the realm of quantum chemistry, the accurate prediction of electronic structure and properties of nanostructures remains a formidable challenge. Density functional theory (DFT) and density matrix renormalization group (DMRG) have emerged as two powerful computational methods for addressing electronic correlation effects in diverse molecular systems. We compare ground-state energies ( e 0 ), density profiles ( n ), and average entanglement entropies ( S ¯ ) in metals, insulators and at the transition from metal to insulator, in homogeneous, superlattices, and harmonically confined chains described by the fermionic one-dimensional Hubbard model. While for the homogeneous systems, there is a clear hierarchy between the deviations, D % (S ¯) < D % (e 0) < D ¯ % (n) , and all the deviations decrease with the chain size; for superlattices and harmonic confinement, the relation among the deviations is less trivial and strongly dependent on the superlattice structure and the confinement strength considered. For the superlattices, in general, increasing the number of impurities in the unit cell represents lower precision in the DFT calculations. For the confined chains, DFT performs better for metallic phases, while the highest deviations appear for the Mott and band-insulator phases. This work provides a comprehensive comparative analysis of these methodologies, shedding light on their respective strengths, limitations, and applications. Methods: The DFT calculations were performed using the standard Kohn-Sham scheme within the BALDA approach. It integrated the numerical Bethe-Ansatz (BA) solution of the Hubbard model as the homogeneous density functional within a local-density approximation (LDA) for the exchange-correlation energy. The DMRG algorithms were implemented using the ITensor library, which is based on the matrix product states (MPS) ansatz. The calculations were performed until the energy reaches convergence of at least 10 - 8 . [ABSTRACT FROM AUTHOR]

Recently, the study of quantum materials through thermal characterization methods has attracted much attention. These methods, although not as widely used as electrical methods, can reveal intriguing physical properties in materials that are not detectable by electrical methods, particularly in electrical insulators. A fundamental understanding of these physical properties is critical for the development of novel applications for energy conversion and storage, quantum sensing and quantum information processing. In this review, we introduce several commonly used thermal characterization methods for quantum materials, including specific heat, thermal conductivity, thermal Hall effect, and Nernst effect measurements. Important theories for the thermal properties of quantum materials are discussed. Moreover, we introduce recent research progress on thermal measurements of quantum materials. We highlight experimental studies on probing the existence of quantum spin liquids, Berry curvature, chiral anomaly, and coupling between heat carriers. We also discuss the work on investigating the quantum phase transitions and quasi-particle hydrodynamics using thermal characterization methods. These findings have significantly advanced knowledge regarding novel physical properties in quantum materials. In addition, we provide some perspectives on further investigation of novel thermal properties in quantum materials. [ABSTRACT FROM AUTHOR]

This Perspective presents an overview of the development of the hierarchy of Davydov's Ansätze and a few of their applications in many-body problems in computational chemical physics. Davydov's solitons originated in the investigation of vibrational energy transport in proteins in the 1970s. Momentum-space projection of these solitary waves turned up to be accurate variational ground-state wave functions for the extended Holstein molecular crystal model, lending unambiguous evidence to the absence of formal quantum phase transitions in Holstein systems. The multiple Davydov Ansätze have been proposed, with increasing Ansatz multiplicity, as incremental improvements of their single-Ansatz parents. For a given Hamiltonian, the time-dependent variational formalism is utilized to extract accurate dynamic and spectroscopic properties using Davydov's Ansätze as its trial states. A quantity proven to disappear for large multiplicities, the Ansatz relative deviation is introduced to quantify how closely the Schrödinger equation is obeyed. Three finite-temperature extensions to the time-dependent variation scheme are elaborated, i.e., the Monte Carlo importance sampling, the method of thermofield dynamics, and the method of displaced number states. To demonstrate the versatility of the methodology, this Perspective provides applications of Davydov's Ansätze to the generalized Holstein Hamiltonian, variants of the spin-boson model, and systems of cavity-assisted singlet fission, where accurate dynamic and spectroscopic properties of the many-body systems are given by the Davydov trial states. [ABSTRACT FROM AUTHOR]

The Schrödinger equation and Bloch theorem are applied to examine a system of protons confined within a periodic potential, accounting for deviations from ideal harmonic behavior due to real-world conditions like truncated and non-quadratic potentials, in both one-dimensional and three-dimensional scenarios. Numerical computation of the energy spectrum of bound eigenfunctions in both cases reveals intriguing structures, including bound states with degeneracy matching the site number Nw, reminiscent of a finite harmonic oscillator spectrum. In contrast to electronic energy bands, the proton system displays a greater number of possible bound states due to the significant mass of protons. Extending previous research, this study rigorously determines the constraints on the energy gap and oscillation amplitude of the previously identified coherent states. The deviations in energy level spacing identified in the computed spectrum, leading to the minor splitting of electromagnetic modes, are analyzed and found not to hinder the onset of coherence. Finally, a more precise value of the energy gap is determined for the proton coherent states, ensuring their stability against thermal decoherence up to the melting temperature of the hosting metal.

In recent years, it has become possible via on‐surface bottom‐up synthesis to engineer the topological character of carbon nanostructures. Graphene nanoribbons and 1D conjugated polymers (1DCPs) have thus tailored so as to host either topologically trivial or non‐trivial phases. Molecular design is the primary means to set the topological class of these nanomaterials. However, external control over topology is also demonstrated via electric fields or top‐down hydrogenation. Inspired by the connection between topology and π‐conjugation, here it is demonstrated via first‐principles calculations that aryl ring twist angles also serve as topological knobs. Focusing on rationally designed 1DCPs composed of triarylmethyl (TAM) units, it is shown that rotation of certain aryl rings enables a transition from the trivial to the topologically non‐trivial phase. Accordingly, fixing a particular twist angle configuration (e.g., via chemical functionalization) is equivalent to robustly setting a targeted topological phase. It is also found that in considered 1DCPs, the quantum phase transition occurs without the electronic band gap closing, due to a multiradical antiferromagnetic phase emerging at the transition point. All in all, this study highlights the potential of aryl ring twisting for engineering topological properties in carbon nanomaterials and establishes TAM 1DCPs as exotic topological 1D systems. [ABSTRACT FROM AUTHOR]

Fractional quantum Hall (FQH) states are exotic quantum many-body phases whose elementary charged excitations are anyons obeying fractional braiding statistics. While most FQH states are believed to have Abelian anyons, the Moore–Read type states with even denominators – appearing at half filling of a Landau level (LL) – are predicted to possess non-Abelian excitations with appealing potential in topological quantum computation. These states, however, depend sensitively on the orbital contents of the single-particle LL wavefunctions and the LL mixing. Here we report magnetotransport measurements on Bernal-stacked trilayer graphene, whose multiband structure facilitates interlaced LL mixing, which can be controlled by external magnetic and displacement fields. We observe robust FQH states including even-denominator ones at filling factors ν = − 9/2, − 3/2, 3/2 and 9/2. In addition, we fine-tune the LL mixing and crossings to drive quantum phase transitions of these half-filling states and neighbouring odd-denominator ones, exhibiting related emerging and waning behaviour. The fractional quantum Hall effect offers a potential platform to harness non-Abelian anyons. Here, the authors report fractional quantum Hall states in trilayer graphene and drive quantum phase transitions between neighbouring states. [ABSTRACT FROM AUTHOR]

The asymmetric quantum Rabi model (AQRM) is a fundamental model in quantum optics describing the interaction of light and matter. Besides its immediate physical interest, the AQRM possesses an intriguing mathematical structure which is far from being completely understood. In this paper, we focus on the distribution of the level spacing, the difference between consecutive eigenvalues of the AQRM in the limit of high energies, i.e. large quantum numbers. In the symmetric case, that is the quantum Rabi model (QRM), the spacing distribution for each parity (given by the Z 2 -symmetry) is fully clarified by an asymptotic expression derived by de Monvel and Zielinski, though some questions remain for the full spectrum spacing. However, in the general AQRM case, there is no parity decomposition for the eigenvalues. In connection with numerically exact studies and recent theoretical results, we describe the spacing distribution for the AQRM which is characterized by a new type of periodicity and symmetric behavior of the distribution with respect to the bias parameter, reflecting the hidden symmetry of the AQRM. In addition, we observe in the AQRM the excited state quantum phase transition for large values of the bias parameter, analogous to the QRM with large qubit energy, and an internal symmetry of the level spacing distribution for fixed bias. This novel symmetry is independent from the symmetry for half-integer bias and not explained by current theoretical knowledge. [ABSTRACT FROM AUTHOR]

Quantum walks are referred to as quantum analogs to random walks in mathematics. They have been studied as quantum algorithms in quantum information for quantum computers. There are two types of quantum walks. One is the discrete-time quantum walk and the other is the continuous-time quantum walk. We study a continuous-time quantum walk on the half line and challenge to find a limit theorem for it in this paper. As a result, approximate behavior of the quantum walker is revealed after the system of quantum walk gets updated in long time. [ABSTRACT FROM AUTHOR]

Four decades since the concept of polyamorphism was introduced by [L. S. Palatnik (1909–1994), Fiz. Nizk. Temp. 25, 400 (1909)], numerous investigations proved its presence in a broad variety of nonmagnetic short-range ordered materials, like structural, metallic, a-metallic, inorganic molecule, orientational, electron glasses, water, ice, carbons, and others. It was manifested by phase transitions between amorphous states as a function of the quench condition and under compression, mediated by long-wave fluctuations of an order parameter. There has been much recent discussion given to the phenomenon of polyamorphism where distinct, different states of amorphous liquids and solids are observed as a function of density. The outstanding contribution of the recently late [A. Sella, et al. (1956–2022), Nat. Mater. 21, 490 (2022)],2 in the field should be recognized here. Underlying this phenomenon is the possibility of a first-order liquid-liquid phase transition driven by the density and entropy differences between the two amorphous phases. Magnetic boost of multilayer graphene under pressure was also recently discovered. Their famous spin counterparts, such as spin liquid, spin ice, and spin glass have been less studied at this end despite numerous similarities, registered so far. Taking that in mind, for further polyamorphism platform development, we demonstrate the signatures of phase transition in spin glass, driven by a magnetic field, and eventually, a novel type of polyamorphism, the spin-glass one. [ABSTRACT FROM AUTHOR]

Superradiant phase transition and entanglement entropy in the Dicke model with a squeezed light are investigated. We find a special rotation coordinate system mapping the original Hamiltonian into an effective dual-oscillator Hamiltonian in the thermodynamic limit. We analytically derive the eigenenergy and eigenstate of the ground state. The ground state is demonstrated to undergo superradiant phase transition at a nonlinear critical boundary collectively induced by the squeezed driving and qubit-field coupling. This phase boundary requires neither large qubit-field detuning nor strong squeezed driving. An exact expression of the ground-state entropy is obtained. We demonstrate that the squeezed light enhances the qubit-field entanglement entropy linearly. [ABSTRACT FROM AUTHOR]

Phase and amplitude modes, also called polariton modes, are emergent phenomena that manifest across diverse physical systems, from condensed matter and particle physics to quantum optics. We study their behavior in an anisotropic Dicke model that includes collective matter interactions. We study the low-lying spectrum in the thermodynamic limit via the Holstein–Primakoff transformation and contrast the results with the semi-classical energy surface obtained via coherent states. We also explore the geometric phase for both boson and spin contours in the parameter space as a function of the phases in the system. We unveil novel phenomena due to the unique critical features provided by the interplay between the anisotropy and matter interactions. We expect our results to serve the observation of phase and amplitude modes in current quantum information platforms. [ABSTRACT FROM AUTHOR]

This work delves into the behavior of cold bosonic atoms within a zigzag optical lattice which offers a rich platform for studying quantum many‐body physics and has potential applications in various fields including quantum simulation, quantum computing, and precision measurement. The study aims to derive exact solutions and explore qualitative properties through dynamical analysis. Exact solutions of the nonlinear differential equation model can provide insights into the behavior of bosonic atoms in complex optical lattice configurations, allowing researchers to simulate and study phenomena such as quantum phase transitions, many‐body localization, and exotic states of matter. The invariant analysis has been performed for the first time on the specified equation, yielding a reduced system of equations with forms that are easier to handle. Novel techniques are applied to extract solutions from the reduced system of equations obtained via invariant analysis. The results reveal a rich set of solutions, including various traveling wave solutions and doubly periodic functions in the form of Jacobian elliptic functions. Bifurcation analysis, conducted through phase portraits, provides insights into the system's long‐term behavior under different parameter values. This work contributes to a deeper understanding of the dynamics of cold bosonic atoms in optical lattices via 2D and 3D plots of obtained solutions depicting the change in the behavior of soliton solutions with fractional derivative parameter. [ABSTRACT FROM AUTHOR]

The physics of a single Josephson junction coupled to a resistive environment is a long-standing fundamental problem at the center of an intense debate, strongly revived by the advent of superconducting platforms with high-impedance multimode resonators. Here we investigate the emergent criticality of a junction coupled to a multimode resonator when the number of modes is increased. We demonstrate how the multimode environment renormalizes the Josephson and capacitive energies of the junction so that in the thermodynamic limit the charging energy dominates when the impedance is larger than the resistance quantum and is negligible otherwise, independently from the bare ratio between the two energy scales and the compact or extended nature of the phase of the junction. Via exact diagonalization, we find that the transition surprisingly stems from a level anticrossing involving not the ground state, but the first excited state, whose energy gap vanishes in the thermodynamic limit. We clarify the nature of the two phases by pointing at a different behavior of the ground and excited states and we show that at the transition point the spectrum displays universality not only at low frequencies. In agreement with recent experiments, we reveal striking spectral signatures of the phase transition. Recent debate challenges the previous understanding of dissipative quantum phase transitions in Josephson junctions linked to resistive environments. This study reexamines the issue with a junction connected to a multimode transmission line, using exact diagonalization to show the transition's emergence with increased system size and clarifying the universal spectrum at the critical point. [ABSTRACT FROM AUTHOR]

Quantum fluctuations in low-dimensional systems and near quantum phase transitions have significant influences on material properties. Yet, it is difficult to experimentally gauge the strength and importance of quantum fluctuations. Here we provide a resonant inelastic x-ray scattering study of magnon excitations in Mott insulating cuprates. From the thin film of SrCuO2, single- and bi-magnon dispersions are derived. Using an effective Heisenberg Hamiltonian generated from the Hubbard model, we show that the single-magnon dispersion is only described satisfactorily when including significant quantum corrections stemming from magnon-magnon interactions. Comparative results on La2CuO4 indicate that quantum fluctuations are much stronger in SrCuO2 suggesting closer proximity to a magnetic quantum critical point. Monte Carlo calculations reveal that other magnetic orders may compete with the antiferromagnetic Néel order as the ground state. Our results indicate that SrCuO2—due to strong quantum fluctuations—is a unique starting point for the exploration of novel magnetic ground states. Magnetic excitations in infinite-layer cuprates have been intensively studied. Here the authors use resonant inelastic x-ray scattering and theoretical calculations to study magnons in thin films of SrCuO2, finding distinct magnon dispersion attributed to renormalization due to quantum fluctuations. [ABSTRACT FROM AUTHOR]

The suppression of ferroquadrupolar order in TmVO4 in a magnetic field is well-described by the transverse field Ising model, enabling detailed studies of critical dynamics near the quantum phase transition. We describe nuclear magnetic resonance measurements in pure and Y-doped single crystals. The non-Kramers nature of the ground state doublet leads to a unique form of the hyperfine coupling that exclusively probes the transverse field susceptibility. Our results show that this quantity diverges at the critical field, in contrast to the mean-field prediction. Furthermore, we find evidence for quantum critical fluctuations present near Tm-rich regions in Y-doped crystals at levels beyond which long-range order is suppressed, suggesting the presence of quantum Griffiths phases. [ABSTRACT FROM AUTHOR]

The quantum phase transition observed experimentally in two-dimensional (2D) electron systems has been a subject of theoretical and experimental studies for almost 30 years. We suggest Gaussian approximation to the mean-field theory of the second-order phase transition to explain the experimental data. Our approach explains self-consistently the universal value of the critical exponent 3/2 (found after scaling measured resistivities on both sides of the transition as a function of temperature) as the result of the divergence of the correlation length when the electron density approaches the critical value. We also provide numerical evidence for the stretched exponential temperature dependence of the metallic phase's resistivities in a wide range of temperatures and show that it leads to correct qualitative results. Finally, we interpret the phase diagram on the density-temperature plane exhibiting the quantum critical point, quantum critical trajectory and two crossover lines. Our research presents a theoretical description of the seminal experimental results. [ABSTRACT FROM AUTHOR]

In this work, we utilize the quantum renormalization-group (QRG) method to investigate quantum phase transitions (QPT) in a one-dimensional anisotropic spin-1/2 XY model with Dzyaloshinskii–Moriya (DM) interaction. Within this model, it has been demonstrated that phase diagrams are influenced by both the anisotropy parameter and DM interaction strength. Particularly noteworthy is our identification of QPT in global entanglement (GE) and tripartite negativity as the number of QRG iterations increases, allowing for a clear distinction between the Spin-fluid and Néel phases. Additionally, both GE and tripartite negativity decrease with rising anisotropy parameter, eventually stabilizing. However, we have observed that the robustness of tripartite negativity exceeds that of GE. To gain deeper insights, we conduct a detailed analysis of the first derivative of GE, unveiling scaling and nonanalytic behavior at the critical point. Our findings provide crucial insights into multipartite entanglement dynamics in condensed matter systems, significantly advancing our understanding of the quantum critical properties in Heisenberg spin models. [ABSTRACT FROM AUTHOR]

We explore the dynamics of l 1 -norm of steered quantum coherence (SQC), steered quantum relative entropy (SQRE), and magic resource quantifier (MRQ) in the one-dimensional XY spin chain in the presence of time-dependent transverse magnetic field. We find that the system's response is highly sensitive to the initial state and magnetic field strength. We show the dynamics of SQC, SQRE, and MRQ revealing the critical point associated with equilibrium quantum phase transition (QPT) of the system. All quantities show maximum at QPT when the initial state is prepared in the ferromagnetic phase. Conversely, they undergo abrupt changes at quantum critical point if the initial state of the system is paramagnetic. Moreover, our results confirm that when quench is done to the quantum critical point, the first suppression (revival) time scales linearly with the system size, and remarkably, its scaling ratio remains consistent for all quenches, irrespective of the initial phase of the system. These results highlight the interplay between the quantum information resources and dynamics of quantum systems away from the equilibrium. Such insights could be vital for quantum information processing and understanding non-equilibrium phenomena in quantum many-body systems. [ABSTRACT FROM AUTHOR]

The Schrödinger equation and Bloch theorem are applied to examine a system of protons confined within a periodic potential, accounting for deviations from ideal harmonic behavior due to real-world conditions like truncated and non-quadratic potentials, in both one-dimensional and three-dimensional scenarios. Numerical computation of the energy spectrum of bound eigenfunctions in both cases reveals intriguing structures, including bound states with degeneracy matching the site number N w , reminiscent of a finite harmonic oscillator spectrum. In contrast to electronic energy bands, the proton system displays a greater number of possible bound states due to the significant mass of protons. Extending previous research, this study rigorously determines the constraints on the energy gap and oscillation amplitude of the previously identified coherent states. The deviations in energy level spacing identified in the computed spectrum, leading to the minor splitting of electromagnetic modes, are analyzed and found not to hinder the onset of coherence. Finally, a more precise value of the energy gap is determined for the proton coherent states, ensuring their stability against thermal decoherence up to the melting temperature of the hosting metal. [ABSTRACT FROM AUTHOR]

In this paper, we develop quantum dynamical methods capable of treating the dynamics of chemically reacting systems in an optical cavity in the vibrationally strong-coupling (VSC) limit at finite temperatures and in the presence of a dissipative solvent in both the few and many molecule limits. In the context of two simple models, we demonstrate how reactivity in the collective VSC regime does not exhibit altered rate behavior in equilibrium but may exhibit resonant cavity modification of reactivity when the system is explicitly out of equilibrium. Our results suggest experimental protocols that may be used to modify reactivity in the collective regime and point to features not included in the models studied, which demand further scrutiny. [ABSTRACT FROM AUTHOR]

[Display omitted] Magnetic impurities in superconductors are of increasing interest due to emergent Yu-Shiba-Rusinov (YSR) states and Majorana zero modes for fault-tolerant quantum computation. However, a direct relationship between the YSR multiple states and magnetic anisotropy splitting of quantum impurity spins remains poorly characterized. By using scanning tunneling microscopy, we systematically resolve individual transition-metal (Fe, Cr, and Ni) impurities induced YSR multiplets as well as their Zeeman effects in the K 3 C 60 superconductor. The YSR multiplets show identical d orbital-like wave functions that are symmetry-mismatched to the threefold K 3 C 60 (1 1 1) host surface, breaking point-group symmetries of the spatial distribution of YSR bound states in real space. Remarkably, we identify an unprecedented fermion-parity-preserving quantum phase transition between ground states with opposite signs of the uniaxial magnetic anisotropy that can be manipulated by an external magnetic field. These findings can be readily understood in terms of anisotropy splitting of quantum impurity spins, and thus elucidate the intricate interplay between the magnetic anisotropy and YSR multiplets. [ABSTRACT FROM AUTHOR]

Lorentz space–time symmetry represents a unifying feature of the fundamental forces, typically manifest at sufficiently high energies, while in quantum materials it emerges in the deep low-energy regime. However, its fate in quantum materials coupled to an environment thus far remained unexplored. We here introduce a general framework of constructing symmetry-protected Lorentz-invariant non-Hermitian (NH) Dirac semimetals (DSMs), realized by invoking masslike anti-Hermitian Dirac operators to its Hermitian counterpart. Such NH DSMs feature purely real or imaginary isotropic linear band dispersion, yielding a vanishing density of states. Dynamic mass orderings in NH DSMs thus take place for strong Hubbard-like local interactions through a quantum phase transition, hosting a non-Fermi liquid, beyond which the system becomes an insulator. We show that depending on the internal Clifford algebra between the NH Dirac operator and candidate mass order-parameter, the resulting quantum-critical fluid either remains coupled with the environment or recovers full Hermiticity by decoupling from the bath, while always enjoying an emergent Yukawa-Lorentz symmetry in terms of a unique terminal velocity. We showcase the competition between such mass orderings, their hallmarks on quasi-particle spectra in the ordered phases, and the relevance of our findings for correlated designer NH Dirac materials. Lorentz symmetry plays a fundamental role in classical to quantum electrodynamics, as well as in quantum chromodynamics, which is typically realized at sufficiently high energies and often exclusively in closed or isolated quantum systems. Here, the authors show that such a fundamental space–time symmetry can also be manifest as an emergent symmetry even in open Dirac systems, when they interact with the surrounding environment. [ABSTRACT FROM AUTHOR]

Nonsymmorphic compounds have attracted much interest owing to their potential nontrivial electronic states. Here, we grew V1−δSb2 single crystal with a nonsymmorphic space group I4/mcm and studied their de Haas–van Alphen oscillations. Orientation-dependent magnetization showed quantum oscillations, allowing determination of the three-dimensional Fermi surface and Berry phase. Our theoretical calculation implied that VSb2's band structures manifest flat bands along the Γ–X path, Dirac band crossings near the P and N points, and in the Γ–Z direction, and nontrivial surface states along the Γ ¯ – Z ¯ line. However, the inconsistencies in observed and calculated quantum oscillation frequencies suggest that VSb2's band structures cannot nicely account for these electronic properties of our samples. This study reveals the profound impact of V vacancies on VSb2's electronic states, implying the possible topological quantum phase transition via defect engineering. [ABSTRACT FROM AUTHOR]

The coherence dynamics of the central systems are investigated in the spin-chain environment with topological characterization. For the single- and two-spin coherence, their critical behaviors can detect the topological quantum phase transitions (TQPTs) in weaker coupling regions. Their noncritical behaviors show periodic oscillations or keep constant. For the quantum coherence of a symmetric W state, the bipartite coherence is dominant due to its polygamy. The critical behaviors of global coherence ( QC a : bc and QC b : c ) and multipartite monogamy can also detect the TQPTs. In the strong coupling regions ( g a (b , c) ≫ 1 ), the coherence dynamics of single-spin, two-spin, and bipartite block of three-spin system can be characterized by Gaussian envelope, but the envelope line of three-spin coherence can be only described by negative logarithmic function. Finally, the resistance to the topological spin-chain environment becomes stronger from the single- to three-spin coherence. [ABSTRACT FROM AUTHOR]

Certain properties of an object only emerge when a sufficient number of those objects are present in a definite arrangement. For example, one or two water molecules cannot said to be in a liquid state, but a drop of water can be. This concept of emergence has been studied extensively, but only occasionally discussed explicitly in the context of chemistry. In this paper, we aim to show the fruitfulness of the concept of emergence for chemical inquiry by considering four case studies of emergent chemical properties, i. e., the liquidity and freezing of water, structural properties of crystals, thermodynamical phase transitions and quantum mechanical phenomena. We show that some of these properties emerge gradually, some at discrete points, and some should be taken to emerge only when the number of constituents tends to infinity. We argue that studying the way in which chemical properties emerge presents a useful avenue for research that promises greater insight into the nature of those properties. [ABSTRACT FROM AUTHOR]

Considering a non-Hermitian version of p-wave Kitaev chain in the presence of additional second nearest neighbour tunnelling, we study dynamical quantum phase transition (DQPT) which accounts for the vanishing Loschmidt amplitude. The locus of the Fisher's zero traces a continuous path on the complex time plane for the Hermitian case while it becomes discontinuous for non-Hermitian cases. This further leads to the half-unit jumps in the winding number characterizing a dynamical topological aspect of DQPT for non-Hermitian Hamiltonian. Uncovering the interplay between non-Hermiticity and long-range tunnelling, we find these features to be universally present irrespective of the additional second nearest neighbour tunnelling terms as long as non-Hermiticity is preserved. The upper panel depicts the discontinuity in Fisher's zeros exactly on the imaginary axis. The lower panel demonstrates the half-qunatized jumps in the dynamical winding number corresponding to such discontinuous jump. [ABSTRACT FROM AUTHOR]

Motivated by an exact mapping between equilibrium properties of a one-dimensional chain of quantum Ising spins in a transverse field (the transverse field Ising (TFI) model) and a two-dimensional classical array of particles in double-well potentials (the " ϕ 4 model") with weak inter-chain coupling, we explore connections between the driven variants of the two systems. We argue that coupling between the fundamental topological solitary waves in the form of kinks between neighboring chains in the classical ϕ 4 system is the analog of the competing effect of the transverse field on spin flips in the quantum TFI model. As an example application, we mimic simplified measurement protocols in a closed quantum model system by studying the classical ϕ 4 model subjected to periodic perturbations. This reveals memory/loss of memory and coherence/decoherence regimes, whose quantum analogs are essential in annealing phenomena. In particular, we examine regimes where the topological excitations control the thermal equilibration following perturbations. This paves the way for further explorations of the analogy between lower-dimensional linear quantum and higher-dimensional classical nonlinear systems. [ABSTRACT FROM AUTHOR]

Long-range interactions are relevant for a large variety of quantum systems in quantum optics and condensed matter physics. In particular, the control of quantum–optical platforms promises to gain deep insights into quantum-critical properties induced by the long-range nature of interactions. From a theoretical perspective, long-range interactions are notoriously complicated to treat. Here, we give an overview of recent advancements to investigate quantum magnets with long-range interactions focusing on two techniques based on Monte Carlo integration. First, the method of perturbative continuous unitary transformations where classical Monte Carlo integration is applied within the embedding scheme of white graphs. This linked-cluster expansion allows extracting high-order series expansions of energies and observables in the thermodynamic limit. Second, stochastic series expansion quantum Monte Carlo integration enables calculations on large finite systems. Finite-size scaling can then be used to determine the physical properties of the infinite system. In recent years, both techniques have been applied successfully to one- and two-dimensional quantum magnets involving long-range Ising, XY, and Heisenberg interactions on various bipartite and non-bipartite lattices. Here, we summarise the obtained quantum-critical properties including critical exponents for all these systems in a coherent way. Further, we review how long-range interactions are used to study quantum phase transitions above the upper critical dimension and the scaling techniques to extract these quantum critical properties from the numerical calculations. [ABSTRACT FROM AUTHOR]

Systems composed of molecular rotors are promising candidates as quantum devices. In this work, we employ our recently developed density matrix renormalization group approach to study such a rotor system, namely, linear chains of rotating para-water molecules encapsulated in a (6,5)-carbon nanotube. We show that the anisotropic environment provided by the nanotube breaks the inversion symmetry of the chain. This symmetry breaking lifts the degeneracy of the ground state and leads to a splitting between the left- and right-polarized states. In turn, a ferroelectric phase in nanoscopic systems is created, with a polarization that can be switched in a manner analogous to that of a supramolecular qubit. We present results for a few low-lying states and discuss the effect of external electric fields on the energy splitting and the occurrence of a quantum phase transition. [ABSTRACT FROM AUTHOR]

Pressure, together with temperature, electric, and magnetic fields, alters the system and allows for the investigation of the fundamental properties of matter. Under applied pressure, the interatomic distances shrink, which modifies the interactions between atoms and may lead to the appearance of new (sometimes exotic) physical properties, such as pressure-induced phase transitions; quantum critical points; new structural, magnetic, and/or superconducting states; and changes of the temperature evolution and symmetry of the order parameters. Muon-spin rotation/relaxation (μ SR) has proven to be a powerful technique in elucidating the magnetic and superconducting responses of various materials under extreme conditions. At present, μ SR experiments may be performed in high magnetic field up to ∼ 9 T, temperatures down to ≃ 10 –15 mK, and hydrostatic pressure up to ∼ 2.8 GPa. In this Perspective, the requirements for μ SR experiments under pressure, the existing high-pressure muon facility at the Paul Scherrer Institute (Switzerland), and selected experimental results obtained by μ SR under pressure are discussed. [ABSTRACT FROM AUTHOR]

We describe a numerical algorithm for approximating the equilibrium-reduced density matrix and the effective (mean force) Hamiltonian for a set of system spins coupled strongly to a set of bath spins when the total system (system + bath) is held in canonical thermal equilibrium by weak coupling with a "super-bath". Our approach is a generalization of now standard typicality algorithms for computing the quantum expectation value of observables of bare quantum systems via trace estimators and Krylov subspace methods. In particular, our algorithm makes use of the fact that the reduced system density, when the bath is measured in a given random state, tends to concentrate about the corresponding thermodynamic averaged reduced system density. Theoretical error analysis and numerical experiments are given to validate the accuracy of our algorithm. Further numerical experiments demonstrate the potential of our approach for applications including the study of quantum phase transitions and entanglement entropy for long range interaction systems. [ABSTRACT FROM AUTHOR]

Spectral line shapes provide a window into the local environment coupled to a quantum transition in the condensed phase. In this paper, we build upon a stochastic model to account for non-stationary background processes produced by broad-band pulsed laser stimulation, as distinguished from those for stationary phonon bath. In particular, we consider the contribution of pair-fluctuations arising from the full bosonic many-body Hamiltonian within a mean-field approximation, treating the coupling to the system as a stochastic noise term. Using the Itô transformation, we consider two limiting cases for our model, which lead to a connection between the observed spectral fluctuations and the spectral density of the environment. In the first case, we consider a Brownian environment and show that this produces spectral dynamics that relax to form dressed excitonic states and recover an Anderson–Kubo-like form for the spectral correlations. In the second case, we assume that the spectrum is Anderson–Kubo like and invert to determine the corresponding background. Using the Jensen inequality, we obtain an upper limit for the spectral density for the background. The results presented here provide the technical tools for applying the stochastic model to a broad range of problems. [ABSTRACT FROM AUTHOR]

We have studied the efficiencies of both classical and quantum heat engines using an Ising model as working fluid and the mean field equation for its non-equilibrium dynamics, formulated earlier (Acharyya et al. J Phys A Math Gen 27:1533, 1994; Acharyya and Chakrabarti Phys Rev B 52:6550, 1995) to study the dynamical hysteresis and the dynamical phase transitions in the quantum Ising ferromagnets. We studied numerically the Ising magnet's nonintegrable coupled nonlinear first order differential equations of motion for a four stroke heat engine and compared the efficiencies in both classical and quantum limits using the quasi-static approximation. In both the pure classical and pure quantum cases, the numerically calculated efficiencies are much less than the corresponding Carnot values. Our analytical formulations of the efficiencies (both in pure classical as well as in pure quantum Ising heat engines) are found to agree well with the numerical estimates. Such formulations also indicate increased efficiency for the mixed case of a transverse field driven Ising engine in presence of nonzero longitudinal field. We also numerically checked and found that the efficiency of such a (mixed) quantum Ising heat engine can indeed have much higher efficiency for appropriate values of the transverse and longitudinal fields. [ABSTRACT FROM AUTHOR]

We investigate the quantum phases and phase transitions for spin–orbit coupled two-species bosons with nearest-neighbor (NN) interaction in a two-dimensional square lattice using inhomogeneous dynamical Guztwiller mean-field method. Under the effect of spin–orbit coupling and NN interaction, we uncover a rich variety of different magnetic supersolid (SS) phases. In the presence of intraspecies NN interaction, the phase diagram exhibits the phase-twisted double-checkerboard SS (PT-DCSS) and phase-striped double-checkerboard SS (PS-DCSS) phases. For both intra- and interspecies NN interactions, apart from the phase-twisted lattice SS (PT-LSS) and phase-striped lattice SS (PS-LSS) phases, some nontrivial SS phases with interesting properties occur. More importantly, we find that the emergences of these nontrivial SS phases are dependent of the interspecies on-site interaction. To further characterize the SS phases, we also discuss the spin-dependent momentum distributions and magnetic textures. The magnetic textures, such as antiferromagnetic, spiral and stripe orders are shown. Finally, we give the fully analytical insights into the numerical results. [ABSTRACT FROM AUTHOR]