Polarization is a significant vector property of the light field that has been widely applied in various fields of modern optical sciences. In this paper, we introduce the concept of polarization into the cavity-magnomechanical system as a platform for studying quantum coherence in the vector regime. Interestingly, we find that quantum coherence can be flexibly and continuously controlled by adjusting the polarization angle of the optical polarizer and implementing coherent switching and role reversal between the two types of photon-magnon-phonon coherences for the transverse electric and transverse magnetic modes. More importantly, this coherent conversion characteristic of quantum coherence exhibits strong robustness to environmental temperature and dissipation channels. In practice, this ability to switch macroscopic quantum coherence would provide another degree of freedom for quantum information science based on the cavity-magnomechanical system. In addition, the experimental feasibility of the polarization-controlled quantum coherence is evaluated, and the strategy for detecting vector quantum coherence is discussed briefly.

We investigate a granular aluminium quantum circuit with an anharmonicity of the order of its decoherence rate in a three-dimensional microwave cavity. We perform single qubitlike manipulations such as Rabi oscillations and Ramsey fringes. Our findings, supported by quantitative numerical modeling, show that a very weakly anharmonic oscillator can also display quantum oscillations outside the qubit regime. These oscillations are hard to disambiguate from qubit oscillations in time domain measurements for a single driving frequency. This sheds light on recent findings for material superconducting quantum bits. Our platform shows in addition large magnetic field resilience which could find applications for quantum enhanced dark matter search.

In previous studies of the half-filled bilayer attractive Hubbard model [Prasad et al., Phys. Rev. A 89, 043605 (2014); Prasad, Phys. Rev. B 106, 184506 (2022)], it has been shown that the clean system has a band-insulator (BI) to superfluid (SF) quantum phase transition. In this paper, we append the effects of random on-site disorder on the kinetic energy, double occupancy, and the pair-pair correlations in the bilayer model. Using the determinant quantum Monte Carlo simulation, we observe that the on-site random disorder plays a significant role in the localization of on-site pairs, and hence in the reduction of the effective hopping. This results in an increase of the double occupancy, which is an effect that is similar to the attractive interaction. We find no change in the critical value of the interaction at which the model undergoes a transition from the BI to SF regime, even though the pair-pair correlations get suppressed for finite on-site disorder strengths $V_d/t=0.1$–0.8. We also confirm that the weak-disorder suppresses the SF phase largely in the strong-coupling limit. Hence the region of the SF phase reduces in the presence of random on-site disorder. Finally, through finite-size scaling, we have estimated the critical disorder strength $V_d^c/t\sim 1.44$ at $\left|U\right|/t=5$.

Understanding the excitation spectrum in two-dimensional quantum many-body systems has long been a formidable challenge. In this study, we propose an innovative approach by introducing an excitation Ansatz based on an infinite matrix product state (MPS) with a helix structure. The use of infinite uniform MPS states allows us to accurately extract key properties such as energy, degeneracy, spectrum weight, and scaling behavior of low-energy excited states simultaneously. To validate the effectiveness of our method, we apply it to the critical point of the transverse-field Ising model. The scaling exponent of the energy gap extracted aligns closely with conformal bootstrap results. Subsequently, we extend our method to the $J_1\text{−}{J}_2$ Heisenberg model on a square lattice. Our findings reveal that the degeneracy of lowest-energy excitations serves as a reliable metric for distinguishing different phases. The phase boundaries identified by our method are consistent with previous findings. The present method provides a promising avenue for studying the excitation spectrum of two-dimensional quantum many-body systems.

The effects of optical bond phonons coupled to electrons in two-dimensional lattices have attracted much interest recently, with the hope to explore unconventional superconducting mechanism and pairing symmetries. Here we conduct a systematic investigation of such phonon modes in the kagome lattice at and around the upper van Hove filling to unravel new effects of the bond phonons in the presence of the unique sublattice frustration. We combine the singular-mode functional renormalization group and the projector determinant quantum Monte Carlo methods. At the upper van Hove filling and in the absence of the Hubbard interaction $U$, we find there exists an $s$-wave superconducting state at weaker electron-phonon coupling constant $\lambda$ and higher phonon frequency $\omega$, and a charge bond order (or the valence bond solid) state at larger $\lambda$ and lower $\omega$. The Hubbard interaction $U$ suppresses drastically the $s$-wave pairing, so that only the charge bond order survives. On the other hand, upon slight doping away from the van Hove filling, we observe that the charge bond order is suppressed due to the breakdown of the perfect Fermi surface nesting, while the superconductivity persists. The $s$-wave superconductivity and charge bond order may be relevant in the layered kagome superconductors ${\mathrm{AV}}_3{\mathrm{Sb}}_5$ (A = K, Rb, Cs).

The photonic properties of a narrow dielectric ring with a rectangular cross section are studied analytically and numerically. It is shown that exceptional points in such a resonator exist in pairs, with each point adjacent in parametric space to a bound state in the continuum, resulting in the formation of quadruplets of singular photonic states. The appearance of quadruplets is determined by the interaction of two photonic branches, which can anticross or intersect in parametric space during the transition from the strong to weak coupling regime, which is described by the Friedrich-Wintgen model. A dielectric ring is an ideal object for modeling quadruplets due to the ability to arbitrarily change the shape of a rectangular cross section, that is, to accurately scan the areas of intersection of axial and radial Fabry-Pérot-like resonances along the height or width of the ring. The key role is played by the internal hole as an additional degree of freedom, which allows one to change the mode coupling coefficient and observe exceptional points. The regimes of electric field concentration inside a narrow dielectric ring at the incidence of a plane electromagnetic wave are also demonstrated. The discovery of quadruplets of singular photonic states is of fundamental importance for the development of the photonics of non-Hermitian structures. The proximity of the exceptional point and the high-$Q$ bound state in the continuum in parametric space allows easy switching between gain and loss regimes and opens up new perspectives for applications.

Photonic analogs of topological crystalline insulators (PTCIs) that host pseudospin-locked unidirectional helical interface states have promising applications for developing novel integrated optical devices. However, current PTCIs are limited to a single polarization. Here, we propose a dual-polarization PTCI hosting topological interface states for both transverse electric (TE) and transverse magnetic (TM) modes. First, we design a photonic crystal (PC), constrained with glide symmetry, with a dual-polarization bulk gap via inverse design. Then, by adopting two kinds of unit cells with different topology indexes from the PC and arranging them to form an interface, pseudospin-locked unidirectional helical interface states are observed. Pseudospin-locked one-way propagations of edge states for both TE and TM modes are demonstrated. Besides the polarization-independent function, we also present the polarization-dependent propagation of interface states by tuning the frequency. Our work demonstrates the flexible manipulation of light in PTCIs with the polarization degree of freedom, having promising applications in developing both polarization-independent and polarization-dependent topological optical devices.

Lowering lattice symmetry plays a pivotal role in generating a nonzero Berry curvature dipole. In this work, we demonstrate that introducing an interlayer sliding in bilayer graphene effectively breaks the inherent threefold rotational symmetry, thus giving rise to a nonzero Berry curvature dipole. Our numerical simulations also reveal the magnitude of the Berry curvature dipole can be further tuned by various parameters, including interlayer sliding distances and directions, as well as interlayer potential differences. We show even a tiny sliding distance of 0.02 nm can lead to a substantial Berry curvature dipole of about 10 nm in bilayer graphene, which is comparable to the values measured in transition metal dichalcogenides (TMDCs). Our work represents a new way to manipulate the topological properties of bilayer graphene, and this methodology can be extended into other two-dimensional systems, such as TMDCs with threefold rotational symmetry.

We study the low-energy eigenstates of a topological superconductor wire modeled by a Kitaev chain, which is connected at one of its ends to a quantum dot through nearest-neighbor (NN) hopping and NN Coulomb repulsion. Using an unrestricted Hartree-Fock approximation to decouple the Coulomb term, we obtain that the quality of the Majorana end states is seriously affected by this term only when the dependence of the low-lying energies with the energy of the quantum dot shows a “diamond” shape, characteristic of short wires. We discuss limitations of the simplest effective models to describe the physics. We expect the same behavior in more realistic models for topological superconducting wires.

We study the topological properties of hardcore bosons on a two-leg ladder consisting of two Su-Schrieffer-Heeger chains that are coupled via hopping and interaction. We chart out the phase diagram for the system and show that based on the relative hopping dimerization pattern along the legs, distinctly different topological phases and phase transitions can occur. When the dimerization along the legs is uniform, we find that the topological nature vanishes for even the slightest rung hopping. For staggered dimerization, the system exhibits a well-defined topological character and a topological phase transition as a function of rung hopping. While the topological phase shows bond order character, the trivial phase shows the behavior of a rung-Mott insulator. For this case, the topological nature is found to survive even in the presence of finite interleg interactions. Moreover, we find that the critical point of the topological phase transition shifts to a higher or a lower rung hopping strength depending on the attractive or repulsive nature of the interaction. To highlight the marked effects of interactions, we propose a scheme involving a Thouless charge pump that provides insights for the topological phases characterized by a quantized particle transport through a periodic modulation of appropriate system parameters. In our studies, we show an interaction-induced charge pumping following specific pumping protocols in the case of staggered dimerization.

Revealing new topological phases is of utmost importance in both Hermitian and non-Hermitian systems due to their potential applications. Generally, topological phases depend on the dimension of the system. Previous studies have shown that five-dimensional (5D) Hermitian systems exhibit certain phases that are not supported by their lower-dimensional counterparts. Here, we investigate the topological properties of 5D non-Hermitian systems and discover topological phases, such as Yang monospheres, Fermi cylinder surfaces, Fermi arcs connecting the two Yang monospheres, and the 5D skin effect. The topological invariants characterizing these phases can be described by both the second Chern number and a quantized Berry phase of the Yang monosphere. Additionally, we conduct experiments on the circuit platform to experimentally confirm the existence of these topological phases. Our findings also leverage the concept of higher-dimension non-Hermitian Weyl physics to control electrical signals in the engineered circuits.

The dual strong-coupling modes facilitate additional energy relaxation channels and broaden spectral enhancements offering promising applications in nanophotonics. However, the dual strong-coupling modes present significant challenges due to limited synergy among coupling types, confinement to visible and infrared excitation, and a lack of relevant studies in the ultraviolet regime, as well as limited tunability. To address these issues, we have theoretically achieved dual strong-coupling modes in both different- and same-band configurations on an Al metasurface. By adjusting the period and diameter of the Al cylinder, it is possible to span both types of dual strong-coupling modes' excitation wavelength from the near ultraviolet to a depth of 329 nm. This work provides ways to adjust coupling wavebands, modulate linewidth, and broaden spectral enhancements.

Non-Hermitian skin effect is a basic phenomenon in non-Hermitian systems, which means that an extensive number of eigenstates can be localized at the boundary. In this Letter, we systematically investigate the constraints from all internal symmetries on the non-Hermitian skin effect in arbitrary dimensions. By adopting the powerful amoeba formulation, we build a generic correspondence between the various internal symmetries and the behavior of the non-Hermitian skin effect. Notably, we find that, for non-Hermitian systems with the Hermitian conjugate symmetry of time-reversal symmetry $\left({\mathrm{TRS}}^{†}\right)$, the eigenstates can simultaneously localize at opposite boundaries, which is beyond the amoeba formulation and we dub the phenomenon bidirectional skin effect. Our work provides an overall perspective from the internal symmetry to the non-Hermitian skin effect.

Inelastic neutron scattering (INS) spectra of hydrogen in face-centered cubic palladium have been calculated considering nuclear quantum effects (NQEs) at finite temperatures. The calculations were performed using semiclassical Brownian chain molecular dynamics (MD) [Shiga, J. Comput. Chem. 43, 1864 (2022)] and artificial neural network potentials with an accuracy of generalized gradient approximation of density functional theory. The calculated spectra are in good agreement with experimental spectra with respect to the peak positions and intensities corresponding to the fundamental tone and the first overtone of the vibrational excitation of hydrogen atoms. These results differ significantly from those of classical MD, indicating that NQE plays an essential role in the correct estimation of the INS spectrum. Importantly, the NQE acts as a blueshift of the INS spectrum for hydrogen in the octahedral site due to strong anharmonic vibrations of hydrogen on the potential surface with even symmetry. The calculated peak shifts associated with Pd lattice distortion were also in agreement with experimental results.

Recently, there has been significant interest in magnon-magnon hybrid systems in the field of spintronics due to their potential for quantum engineering. Achieving strong coupling, and even ultrastrong coupling (USC), is crucial for enhancing the efficiency of quantum information processing. While the strong coupling has been widely observed in magnon-magnon hybrid systems, the USC has been rarely reported. Therefore, the current focus of research is to explore more possible mechanisms for realizing magnon-magnon USC. Here, we highlight that the interlayer Dzyaloshinskii-Moriya interaction (DMI) can break the rotation symmetry in synthetic antiferromagnets (SAFs) when the DMI vector D is nonorthogonal to the external dc magnetic field. As a result, magnon-magnon coupling can be induced by the interlayer DMI, as confirmed by both macrospin model and micromagnetic simulations. We suggest that the strength of magnon-magnon coupling can be tuned to a considerable degree by properly selecting the direction of D and adjusting the material parameters of SAF, such as the magnetic anisotropy field, the effective interlayer DMI field, and the effective Ruderman-Kittel-Kasuya-Yosida interaction field. Surprisingly, a sudden increase of coupling strength takes place when the total magnetic anisotropy field changes the sign. We emphasize that within this region, the coupling properties exhibit high sensitivity to anisotropy, and even an extremely small interlayer DMI intensity can induce the USC. The maximum normalized coupling strength in this region can surpass 0.5, which is far in excess of the commonly used value 0.1 that is considered as a requirement for establishing USC. These results place SAFs with interlayer DMI in focus for the future study of magnon-magnon USC, which can be of considerable interest for the experimental research.

We investigate the magnetoelectric coupling in ${\mathrm{CaMn}}_7{\mathrm{O}}_{12}$ (CMO) through a comprehensive spectroscopic analysis combining inelastic neutron scattering (INS), x-ray absorption spectroscopy (XAS), and synchrotron-based powder x-ray diffraction (PXRD). CMO's intricate interplay between magnetism and ferroelectricity is dissected to uncover its underlying mechanisms. XAS reveals a mixed valency of Mn ions in CMO, reflecting the presence of ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ ions, which contributes to its magnetoelectric properties. The double structure in Mn-$K$ near-edge absorption spectra reinforces multiple Mn sites as well as the mixed valency of the compound. Synchrotron-based PXRD experiments conducted over a range of temperatures unveil structural distortions near the magnetic transition temperatures of CMO. These distortions coincide with anomalies in lattice parameters and bond lengths, shedding light on the link between structural modulations and magnetoelectric behavior. Furthermore, INS measurements identify specific energy bands ($E_1$, $E_2$, and $E_3$) associated with distinct exchange interactions between Mn ions. This work advances our understanding of magnetoelectric coupling mechanisms and showcases the potential of multifunctional materials for applications in spintronics and related fields.

In this study, we investigated the performance of two 2D superconducting quantum interference filter (SQIF) arrays fabricated from YBCO thin films at a temperature of 77 K. Each array consisted of 6 Josephson junctions (JJs) in parallel and 167 in series. We conducted both experimental and theoretical analyses, measuring the arrays' voltage responses to an applied magnetic field and their voltage versus bias-current characteristics. To properly model the planar array layouts, our theoretical model used the stream function approach and also included the Johnson noise in the JJs. The model further divides the superconducting current density of the arrays into its Meissner current, circulating current, and bias current parts for practicality. Since the fabrication process of YBCO thin films cannot produce identical JJ critical currents, we assumed a log-normal distribution to model the JJ critical current disorder. Our model predictions, with a JJ critical current spread of 50%, agreed well with our experimental data. Using our model, we were able to study the dependence of the voltage modulation depth on critical current disorder and London penetration depth. We also analyzed the observed reflection asymmetries of the voltage versus magnetic field characteristics, which might provide insight into the degree of critical current disorder. Overall, our findings suggest that the use of YBCO thin films in SQIF arrays is promising, despite the critical current disorder inherent in their fabrication process. Our study highlights the importance of theoretical modeling in understanding the performance of superconducting devices and provides insights that could inform the design of future SQIF arrays.