Long-range State Research Articles

Long-range generation of a magnon-magnon entangled state

Generation of entanglement between spatially separated macroscopic systems enables quantum networks and fundamental tests of quantum theory. Here, we propose a scheme to generate a long-range entangled state between two macroscopic spheres. The hybrid system under consideration consists of two massive ferromagnetic spheres and a superconducting transmon qubit, which are both coupled to a microwave cavity array. When the qubit or magnon frequency lies outside of the frequency band of the cavity array, the qubit or magnon mode can seed a tunable, localized cavity mode with an exponentially decaying envelope around its position. This effective cavity mediates the long-range qubit-magnon and magnon-magnon interactions in a coherent way, enabling the long-distance magnon-magnon entanglement via the superconducting qubit.

Donor multiple effects on the ferroelectric and piezoelectric performance of lead-free BiFeO3-BaTiO3 ceramics

Nb-modified lead-free 0.67Bi1.03FeO3-0.33BaTi1-xNbxO3 ceramics were synthesized by a solid-state reaction combined with a quenching process and investigated in terms of ferroelectric and piezoelectric properties. The Nb modification induced a phase change from the rhombohedral and tetragonal mixed-phase to the pseudocubic phase. This chemical modification transforms the long-range ferroelectric state to a short-range relaxor ferroelectric state. As a result, an excellent piezoelectric performance (d33 = 285 pC/N and d33* = 403 pm/V) with high a Curie temperature, 473 °C and low piezoelectric strain hysteresis, 20% were achieved. Furthermore, high d33* at a very low field 25 kV/cm and the temperature-insensitive piezoelectric response suggest highly promising results in the lead-free BF-BT ceramics. It is believed that the high piezoelectric response is related to multiple effects such as crystal structure of morphotropic phase boundary, an optimum grain size (≈5 μm), high lattice distortion (cT/aT = 1.01) and soft-ferroelectric effect induced by the donor-doping.

Relationship between Short-Range and Homotopic Long-Range Resting State Functional Connectivity in Temporal Lobes in Autism Spectrum Disorder.

To investigate the relationship between short-range and homotopic long-range resting state functional connectivity (RSFC) in children with autism spectrum disorder (ASD) and typically developing (TD) children, we analyzed functional near-infrared spectroscopy (fNIRS) RSFC in 25 children with ASD and 22 age-matched TD children. The resting state fNIRS signals, including spontaneous fluctuations in the oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb) concentrations, were recorded from the bilateral temporal lobes. We found that (1) there was no difference in the short-range RSFC between the left and right hemisphere in either ASD or TD group; (2) both the short-range and homotopic long-range RSFC were weaker in the ASD than TD group; and (3) the short-range RSFC was stronger than the homotopic long-range RSFC in the ASD group, whereas no such difference was observed in the TD group. These observations might be helpful for a better understanding of the underlying cortical mechanism in ASD.

Coupling-modulation–mediated generation of stable entanglement of superconducting qubits via dissipation

We propose an experimentally feasible scheme for the dissipative generation of stable entanglement of superconducting qubits via coupling modulation without applying any drives on qubits and resonator. Firstly, we study the circuit of one superconducting transmission line resonator coupled to two separated qubits via two superconducting quantum interference devices (SUQIDs). By modulating the inductance of the SQUIDs via external fluxes, we can tailor an appropriate qubit-resonator coupling with both red- and blue-sideband interactions. Combined with the photon loss of the resonator, the two qubits can be autonomously steered into a long-lived entangled state with high fidelity. Moreover, we extend the model to one resonator coupled to two separated qubit chains, each of which contains N linearly coupled superconducting qubits. We show that the lossy resonator can drive the whole system into a unique dark state, i.e., a series of N entangled pairs of qubits across the chains can be stabilized at the stationary state. So, the present work enables the preparation of a stable long-range entangled state between the two qubits in the end sites of the chains, which plays an important role for implementing scalable quantum computation and quantum communication.

Symmetric U(1) and Z2 spin liquids on the pyrochlore lattice

The geometrically frustrated 3D pyrochlore lattice has been long predicted to host a quantum spin liquid, an intrinsic long-range entangled state with fractionalized excitations. To date, most proposals for pyrochlore materials have focused on quantum spin ice, a $\mathrm{U(1)}$ quantum spin liquid whose only low energy excitations are emergent photons of Maxwell type. In this work, we explore the possibility of finding pyrochlore quantum spin liquids whose low energy theories go beyond this standard one. We give a complete classification of symmetric $\mathrm{U(1)}$ and $\mathbb{Z}_2$ spin liquids on the pyrochlore lattice within the projective symmetry group framework for fermionic spinons. We find 18 $\mathrm{U(1)}$ spin liquids and 28 $\mathbb{Z}_2$ spin liquids that preserve pyrochlore space group symmetry while, upon further imposing time reversal symmetry, the numbers of classes become 16 and 48, respectively. For each class, the most general symmetry-allowed spinon mean-field Hamiltonian is given. Interestingly, we find that several $\mathrm{U(1)}$ spin liquid classes possess an unusual gapless multi-nodal-line structure ("nodal star") in the spinon bands, which is protected by the projective actions of the three-fold rotation and screw symmetries of the pyrochlore space group. Through a simple model, we study the effect of gauge fluctuations on such a nodal star spin liquid and propose that the leading terms in the low temperature specific heat have the scaling form $C/T\sim \sqrt{T}+\sqrt{T}/\ln T$, in contrast to the form $C/T \sim T^2$ of the standard $\mathrm{U(1)}$ pyrochlore spin liquid with gapped spinons.

Q = 0 order in quantum kagome Heisenberg antiferromagnet

We have studied the nearest neighbor Heisenberg model with added Dzyaloshinskii–Moriya interaction using Schwinger boson mean-field theory considering the in-plane component as well as out-of-plane component. Motivated by the experimental result of vesignieite that the ground state is in a Q = 0 long-range order state, we first looked at the classical ground state of the model and considered the mean-field ansatz which mimics the classical ground state in the large S limit. We have obtained the ground-state phase diagram of this model and calculated properties of different phases. We have also studied the above model numerically using exact diagonalization up to a system size N = 30. We have compared the obtained results from these two approaches. Our results are in agreement with the experimental result of the vesignieite.

Long-range magnetic ordering in Li2MnGeO4 and precursor short-range spin correlations

Long-range magnetic ordering and short-range spin correlations in layered noncentrosymmetric orthogermanate ${\mathrm{Li}}_{2}\mathrm{MnGe}{\mathrm{O}}_{4}$ were studied by means of polarized and unpolarized neutron scattering. The combined Rietveld refinement of synchrotron and neutron powder diffraction data at room temperature within the $Pmn{2}_{1}$ space group allowed us to specify the details of the crystal structure. According to the additional Bragg peaks in low-temperature neutron diffraction patterns a long-range antiferromagnetic ordering with the propagation vector $k=\phantom{\rule{0.16em}{0ex}}(1/2\phantom{\rule{0.16em}{0ex}}1/2\phantom{\rule{0.16em}{0ex}}1/2)$ has been found below ${T}_{N}\ensuremath{\approx}8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Symmetry analysis revealed the model of the ground state spin structure within the ${C}_{a}c$ (no. 9.41) magnetic space group. It is represented by the noncollinear ordering of manganese atoms with a refined magnetic moment of $4.9\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/{\mathrm{Mn}}^{2+}$ at 1.7 K, which corresponds to the saturated value for the high-spin configuration $S=5/2$. Diffuse magnetic scattering was detected on the neutron diffraction patterns at temperatures just above ${T}_{N}$. Its temperature evolution was investigated in detail by polarized neutron scattering with the following XYZ-polarization analysis. Reverse Monte Carlo simulation of diffuse scattering data showed the development of short-range ordering in ${\mathrm{Li}}_{2}\mathrm{MnGe}{\mathrm{O}}_{4}$, which is symmetry consistent on a small scale with the long-range magnetic state below ${T}_{N}$. The reconstructed radial spin-pair correlation function $S(0)\phantom{\rule{0.16em}{0ex}}S(r)$ displayed the predominant role of antiferromagnetic correlations. It was found that spin correlations are significant only for the nearest magnetic neighbors and almost disappear at $r\ensuremath{\approx}12\phantom{\rule{0.16em}{0ex}}\AA{}$ at 10 K. Temperature dependence of the diffuse scattering implies short-range ordering long before the magnetic phase transition. Besides, the spin arrangement was found to be similar in both cases above and below ${T}_{N}$. As a result, an exhaustive picture of the gradual formation of magnetic ordering in ${\mathrm{Li}}_{2}\mathrm{MnGe}{\mathrm{O}}_{4}$ is presented.

Nanomagnonic Cavities for Strong Spin-Magnon Coupling and Magnon-Mediated Spin-Spin Interactions.

We present a theoretical approach to use ferromagnetic or ferrimagnetic nanoparticles as microwave nanomagnonic cavities to concentrate microwave magnetic fields into deeply subwavelength volumes ∼10^{-13} mm^{3}. We show that the field in such nanocavities can efficiently couple to isolated spin emitters (spin qubits) positioned close to the nanoparticle surface reaching the single magnon-spin strong-coupling regime and mediate efficient long-range quantum state transfers between isolated spin emitters. Nanomagnonic cavities thus pave the way toward magnon-based quantum networks and magnon-mediated quantum gates.

Dynamical preparation of a steady off-diagonal long-range order state in the Hubbard model with a local non-Hermitian impurity

The cooperation between non-Hermiticity and interaction brings about a lot of counterintuitive behaviors, which are impossible to exist in the framework of the Hermitian system. We study the effect of a non-Hermitian impurity on the Hubbard model in the context of $\ensuremath{\eta}$ symmetry. We show that the non-Hermitian Hubbard Hamiltonian can respect a full real spectrum even if a local non-Hermitian impurity is applied to. The balance between dissipation of single fermion and on-site pair fluctuation results in a highest-order coalescing state with off-diagonal long-range order (ODLRO). Based on the characteristic of high-order EP, the critical non-Hermitian Hubbard model allows the generation of such a steady superconducting-like state through the time evolution from an arbitrary initial state, including the vacuum state. Remarkably, this dynamic scheme is insensitive to the on-site interaction and entirely independent of the locations of particle dissipation and pair fluctuation. Our results lay the groundwork for the dynamical generation of a steady ODLRO state through the critical non-Hermitian strongly correlated system.

Magnonic Superfluidity Versus Bose Condensation

This article discusses two different coherent quantum phenomena of magnonic bosons: Bose–Einstein condensation (mBEC) and Superfluid State of Magnons (SSM). What is the difference between the two? Magnon BEC is a quantum phenomenon determined by local density of bosonic quasiparticles. The superfluid state of magnons is a long-range coherent quantum state characterized by the rigidity of the order parameter. This is similar to the states of mass superfluidity and superconductivity. In this state, the deflected magnetization can coherently precess even in a strongly inhomogeneous magnetic field. The magnons superflow restore the coherence of SSM after a perturbation. The critical Landau velocity of the coherent magnon flow is determined by an energy gap arising from the repulsion of magnons. This article describes in detail the mechanism of SSM formation.

Fractionalization and anomalies in symmetry-enriched U(1) gauge theories

We classify symmetry fractionalization and anomalies in a (3+1)d U(1) gauge theory enriched by a global symmetry group $G$. We find that, in general, a symmetry-enrichment pattern is specified by 4 pieces of data: $\rho$, a map from $G$ to the duality symmetry group of this $\mathrm{U}(1)$ gauge theory which physically encodes how the symmetry permutes the fractional excitations, $\nu\in\mathcal{H}^2_{\rho}[G, \mathrm{U}_\mathsf{T}(1)]$, the symmetry actions on the electric charge, $p\in\mathcal{H}^1[G, \mathbb{Z}_\mathsf{T}]$, indication of certain domain wall decoration with bosonic integer quantum Hall (BIQH) states, and a torsor $n$ over $\mathcal{H}^3_{\rho}[G, \mathbb{Z}]$, the symmetry actions on the magnetic monopole. However, certain choices of $(\rho, \nu, p, n)$ are not physically realizable, i.e. they are anomalous. We find that there are two levels of anomalies. The first level of anomalies obstruct the fractional excitations being deconfined, thus are referred to as the deconfinement anomaly. States with these anomalies can be realized on the boundary of a (4+1)d long-range entangled state. If a state does not suffer from a deconfinement anomaly, there can still be the second level of anomaly, the more familiar 't Hooft anomaly, which forbids certain types of symmetry fractionalization patterns to be implemented in an on-site fashion. States with these anomalies can be realized on the boundary of a (4+1)d short-range entangled state. We apply these results to some interesting physical examples.

Bichromatic Photoassociation Spectroscopy for the Determination of Rotational Constants of Cs2 0 u + Long-Range State below the 6S1/2 + 6P1/2 Asymptote.

This article demonstrates new observation of the high-resolution ro-vibrational bichromatic photoassociation spectra (BPAS) of Cs2 in the long-range state below the asymptotes 6S1/2 + 6P1/2. By combining with a modulation spectroscopic technique, precise references of the frequency differences have been engineered through the BPAS, with which the rotational constants of low-lying vibrational levels of the Cs2 long-range state have been accurately determined by fitting the frequency differences to the non-rigid-rotor model. The rotational constants for the newly observed seven ro-vibrational levels are summarized and disagreement for the level ῦ = 498 is clarified. The rotational constants of different vibrational levels demonstrate strong perturbations of the related energy structures. A simple analysis is performed and shows good agreement with experimental results.

Long-Range Ordered Water Correlations between A–T/C–G Nucleotides

Summary The interactions between complementary base pairs are crucial to the helical duplex structure of DNA. Although base-base interactions have been widely reported, the study of long-range interactions in the base-pairing processes is still a major challenge in this field. Here, we first study the long-range interactions between the base pairs by atomic force microscopy-based single-molecule force spectroscopy (SMFS). The SMFS results of A–T/C–G imply that there are weak long-range interactions between them, which have a range of 15–25 nm. Raman spectroscopy results imply that these weak interactions can be attributed to multiplex hydrogen bond interaction of ordered water structure between A–T/C–G nucleotides. In addition, the theoretical calculations deduce that the ideal structure of these water molecules exhibits a specific helical structure. Our findings might open up a new understanding of biological assembly processes and provide helpful strategies for bio-nanotechnology.

A transient superconductor

Physics Systems of interacting particles occupying a lattice can often be described by the so-called Hubbard model. This model has been studied extensively with cold atoms in optical lattices, where its parameters can be easily tuned. In a complementary approach, Buzzi et al. investigated the organic molecular superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br, which can be described by the model, and used light to modulate the Hubbard parameters. The frequency of the light was tuned to a vibrational mode of the molecular building block of this material. The photoexcitation caused the sample to (briefly) become superconducting at temperatures much higher than the critical temperature. Calculations indicated that this was a consequence of an unusual long-range state of doubly occupied lattice sites. Phys. Rev. X 10 , 031028 (2020).

Magnetic critical behavior in the intermetallic compound (Ce0.65Pr0.35)2Co7

Clarification of magnetic phase transition nature and critical behavior is an essential step in the development of new magnetic functional materials. In this work, we studied critical properties of intermetallic compound (Ce0.65Pr0.35)2Co7 by bulk dc magnetization around the paramagnetic to ferromagnetic phase transition. It exhibits a second-order magnetic phase transition with TC = 214 K. Critical exponents β = 0.546(5) and γ = 1.054(5) are obtained by the modified Arrott plot, whereas δ = 2.843 is obtained by a critical isotherm analysis at TC. These critical exponents not only obey the Widom relation δ = 1 + γ/β, but also collapse the isothermal magnetization M-H-T data into two branches below and above TC following the single scaling equation M(H, ε) = εβf±(H/εβ+γ). Although the obtained exponents are close to the theoretical values of mean-field model, a noticeable deviation unable to be ignored, indicating the existence of localized magnetic interaction which competes with a long-range ferromagnetic state. Our results will establish a sound theoretical basis for understanding the complex magnetic interaction in the light rare earths ternary alloy.

Suppression of Metamagnetic Transitions of Martensitic Type by Particle Size Reduction in Charge-Ordered La0.5Ca0.5MnO3

In this paper, we have studied the effect of size reduction on charge ordering (CO) and magnetic phase separation in La0.5Ca0.5MnO3. The magnetic ground state at low temperature shifts from ferromagnetic (nanoparticles) to CO-antiferromagnetic (bulk) with increasing annealing temperature. The studied samples exhibit relevant phenomena such as Griffiths phase and training effect. Magnetic field cycling can stabilize ferromagnetic or antiferromagnetic domains, depending on the temperature value as well as the sample’s nature. For the compound sintered at 1200 °C, step-like metamagnetic transitions of martensitic type were observed at 4 K, indicating the presence of weak spin-phonon coupling. The disappearance of magnetic phase separation at 4 K (the sample is purely antiferromagnetic) can be a possible origin for the occurrence of such transitions. Lowering the sintering temperature leads to the disappearance of martensitic transitions. The obtained results indicate that the occurrence of step-like metamagnetic transition of martensitic type necessarily requires the onset of a long-range CO-antiferromagnetic state.

Reduction of thermal conductivity in ferroelectric SrTiO3 thin films

Bulk ${\mathrm{SrTiO}}_{3}$ is a quantum paraelectric in which an antiferrodistortive distortion below $\ensuremath{\approx}105$ K and quantum fluctuations at low temperature preclude the stabilization of a long-range ferroelectric state. However, biaxial mechanical stress, impurity doping, and Sr nonstoichiometry, among other mechanisms, are able to stabilize a ferroelectric or relaxor ferroelectric state at room temperature, which develops into a longer-range ferroelectric state below 250 K. In this paper, we show that epitaxial ${\mathrm{SrTiO}}_{3}$ thin films grown under tensile strain on ${\mathrm{DyScO}}_{3}$ exhibit a large reduction of thermal conductivity, of $\ensuremath{\approx}60%$ at room temperature, with respect to identical strain-free or compressed films. The thermal conductivity shows a further reduction below 250 K, a temperature concurrent with the peak in the dielectric constant [J. H. Haeni et al., Nature (London) 430, 758 (2004)]. These results suggest that strain gradients in the relaxor and ferroelectric phase of ${\mathrm{SrTiO}}_{3}$ are very effective phonon scatterers, limiting the thermal transport in this material.

Combined effect of magnetic field and hydrostatic pressure on the phase transitions exhibited by Ni-Mn-In metamagnetic shape memory alloy

We present a systematic study of the magnetostructural and magnetic transitions in the prototype metamagnetic shape memory alloy Ni50Mn34.5In15.5 under hydrostatic pressure and combined pressure and magnetic field. Pressure extends the area of stability of the antiferromagnetic martensitic phase. At low magnetic field the pressure derivatives of the Curie temperatures of austenite, TCA, and martensite, TCM, show opposite signs. This fact is described in the framework of the Landau thermodynamic model as arising from a weak long-range antiferromagnetic state of martensite. Two volume magnetoelastic constants were estimated using the experimental values of the pressure derivatives of TCA and TCM. A correlation between the signs of the pressure shifts of TCA, and TCM and the distance between Mn-Mn nearest neighbours is established, which matches the empirical Castelliz-Kanomata diagram. The entropy change at martensitic transformation (MT), ΔSMT, grows up when the MT temperature, TM, is approaching TCA under the influence of pressure, but under constant non-zero pressure this dependence is inverse.

Fractal analysis of seismoacoustic signals of near-surface sedimentary rocks in Kamchatka

We studied, by the mono- and multifractal detrended fluctuation analysis (DFA), time fluctuations in the dynamics of seismoacoustic data, recorded in Karymshina site, which is located in a seismic area of Kamchatka. We took a series of seismoacoustic responses to the regional seismic events with the mag-nitudes M > 4 for the period 2017–2018. The series was divided into three groups (high, medium and low) based on the amplitude of recorded seismoacoustic re-sponse. Background noise segments of the signals demonstrated monofractal behavior similar to white noise by almost constant values of generalized Hurst exponent Hq≈0.5 and very small width of the multifractal spectrum Δa ≈ 0.1. Analysis of the high amplitude seismoacoustic signals with clear P-, S- and coda waves showed that P- and S-waves demonstrate wider multifractal spectrum (ΔaP = 0.37, ΔaS = 0.35) and range of generalized Hurst exponents Hq in com-parison with coda wave, characterized by almost constant Hq and minimal width of multifractal spectrum (ΔaCODA = 0.13). We showed that the properties of the multifractal spectrum could be used in detection of seismic wave arrival, estima-tion its duration and separation of P-, S- and coda waves. Application of the monofractal DFA in a sliding window showed that the acoustic signal transits from monofractal and uncorrelated background noise (Hurst exponent equals to 0.5) into the long-range dependent state during seismic waves arrival, that is helpful in analysis of the signals, particularly in case of low amplitude acous-tic responses, usually demonstrating an unclear waveform. Difference in mul-tifractal spectrum width between the original low amplitude signal and its sur-rogates, obtained by random shuffling showed that the multifractality in the signal is dominantly due to long-range correlations.

Long-range entangled-plaquette states for critical and frustrated quantum systems on a lattice

We explore a variational Ansatz for lattice quantum systems---named long-range entangled-plaquette state---in which pairs of clusters of adjacent lattice sites are correlated at any distance. The explicit scale-free structure of correlations built in this wave function makes it fit to reproduce critical states with long-range entanglement. The use of complex weights in the Ansatz allows for an efficient optimization of nonpositive definite states in a fully variational fashion, namely without any additional bias (arising, e.g., from pre-imposed sign structures) beyond that imposed by the parametrization of the state coefficients. These two features render the Ansatz particularly appropriate for the study of quantum phase transitions in frustrated systems. Moreover, the Ansatz can be systematically improved by increasing the long-range plaquette size, as well as by the inclusion of even larger adjacent-site plaquettes. We validate our Ansatz and its optimization procedure in the case of the XX and Heisenberg chain, and further apply it to the case of a simple, yet paradigmatic model of frustration, namely the ${J}_{1}\ensuremath{-}{J}_{2}$ antiferromagnetic Heisenberg chain. For this model we provide clear evidence that our trial wave function faithfully describes both the short-range physics (particularly in terms of ground-state energy) and the long-range one expressed by the Luttinger exponent, and the central charge of the related conformal field theory, which govern the decay of correlations and the scaling of the entanglement entropy, respectively. Finally we successfully reproduce the incommensurate correlations developing in the system at strong frustration, as a result of the flexible representation of sign (phase) structures via complex weights.