We study the periodic entanglement and asymmetric steering at exceptional points for a non-Hermitian cavity magnetomechanics system in which exceptional points (EPs) emerge periodically by controlling the relative phase angle of the nanoparticles. First, we analyze this hybrid system and identify parametric regimes where different types of entanglement and steering are enhanced. Entanglement and steering can be significantly enhanced due to the external control method and are thus more robust to thermal noises. This provides an active method to manipulate the asymmetry of steering instead of adding asymmetric losses or noises to subsystems at the cost of reducing steering ability. Moreover, the relative phase angle (RPA) not only enhances the strength of entanglement but also increases the domain of entanglement over a wider space of detunings compared to a system in which no RPA is present. Another important consequence of the RPA is that it controls the directivity of quantum steering. Specifically, steering reaches a maximal value at EPs as well, and we can get rich properties of Einstein-Podolsky-Rosen steering; e.g., the asymmetry of the overall state is stepwise, including one-way quantum steering, no-way quantum steering, and two-way quantum steering. We believe that the presented scheme is a step forward in realizing robust quantum entanglement using current technology. Our results indicate that cavity magnetomechanics systems could provide a promising platform for the study of macroscopic quantum phenomena.

Recent observations of unconventional superconductivity (SC) in thin films of ${\mathrm{LaNiO}}_2$ (critical temperature $T_{\mathrm{c}}\simeq$ 10 K) and in bulk single crystals of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under pressure $T_{\mathrm{c}}\simeq 80\mathrm{K}$ have cemented a long sought-after class of SC nickelates. In ${\mathrm{La}}_{1-x}\mathrm{Sr}{}_x{\mathrm{NiO}}_2$, SC appears only in films for reasons not understood. We perform a combination of experiments to probe the crystal structure and magnetic order in bulk ${\mathrm{LaNiO}}_2$ together with ab initio calculations of the electronic structure. We find that the infinite layers are naturally buckled out-of-plane. The electronic bands are largely unaffected by the buckling, but uniaxial compression along the $c$ axis may lead to a Lifshitz transition.

The $d$-wave pairing symmetry in newly discovered infinite-layer nickelates remains highly debated compared to the widely accepted $d$-wave superconductivity in cuprates, despite recent intense efforts using equilibrium optical and electrical transport measurements. A complementary approach involves characterizing THz coherent nonlinear responses, which is currently lacking but needed, as it would offer new insights into the superconducting gap structure by characterizing Higgs modes and quasiparticle excitations. Here, we report THz 2D coherent spectroscopy (THz-2DCS) responses from the superconducting state in an infinite-layer nickelate. The 2D spectra clearly demonstrate the absence of hallmark signatures of $s$-wave pairing symmetry, such as resonant $2\mathrm{\Delta }$ peaks at superconducting gaps. Instead, we observe gapless 2D spectra in the nickelate, centered around the THz driving frequency, with no noticeable shift as the temperature increases. These findings closely resemble the nodal superconductivity behavior expected in cuprates. Together with our simulations, these findings suggest that $2\mathrm{\Delta }$ signatures in the 2D spectra of $d$-wave gap structures can be obscured by significant nodal quasiparticle excitations at arbitrarily low energies. This contrasts with the long-lived Higgs modes, observed as distinct $2\mathrm{\Delta }$ peaks in a controlled THz-2DCS experiment on niobium, a representative example of dirty-limit s-wave superconductors. Our results have implications for understanding the unconventional superconductivity in nickelates and highlight the need to explore their coherent nonlinear dynamics.

We propose the Symmetry topological field theory (TFT) for theories with a $U\left(1\right)$ symmetry in arbitrary dimension. The Symmetry TFT describes the structure of the symmetry, its anomalies, and the possible topological manipulations. It is constructed as a BF theory of gauge fields for groups $U\left(1\right)$ and $\mathbb{R}$, and contains a continuum of topological operators. We also propose an operation that produces the Symmetry TFT for the theory obtained by dynamically gauging the $U\left(1\right)$ symmetry. We discuss many examples. As an interesting outcome, we obtain the Symmetry TFT for the noninvertible $\mathbb{Q}/\mathbb{Z}$ chiral symmetry in four dimensions.

Photoinduced phase transitions (PIPTs) allow complex interactions to be distinguished within the constraints of atomic motion. Here, using real-time time-dependent density functional theory (rt-TDDFT) simulations combined with occupation-constrained density functional theory (DFT) methods, we reveal the ultrafast dynamics of ${\mathrm{ReS}}_2$ monolayer driven by photoexcitation at varying levels of electronic occupancy. The results show that the phase transition from diamond-shaped to zigzag-shaped to quasi-diamond-shaped (DS-ZS-${\mathrm{DS}}^{\prime }$) is effectively induced by $4\%$ excitation manually, resulting in the formation of new quasidiamond chains along the direction of the original diamond chains rotated by $\pi /3$. Notably, under pulse excitation, the entire dynamic process also includes subsequent recovery, during which the quasidiamond chains rotate back to their original direction. The phase transition is mediated by the atomic force caused by photoexcited electrons occupying the antibonding state of the Re-Re bonds between the ${\mathrm{Re}}_4$ diamonds, accompanied by the modulation of the potential energy surface. The thermal phonon vibration can effectively reduce the optical excitation fluency required to drive the bond dissociation and rearrangement. These findings provide an important guiding significance for nonequilibrium phase regulation.

Detecting the topological Kosterlitz-Thouless (KT) transition in the prototypical two-dimensional (2D) XY model using unsupervised machine learning methods has long been a challenging problem due to the lack of suitable order parameters. To address this issue, we begin with a conventional real-valued restricted Boltzmann machine (RBM) (RBM-xy), which uses exponential conditional probabilities to generate visible units. We then develop a novel real-valued RBM (RBM-CosSin) featuring nonlinear $cos/sin$ activation, whose visible units follow the von Mises distribution. Our findings reveal that RBM-CosSin effectively learns the underlying Boltzmann distribution of 2D XY systems and generates authentic XY configurations that accurately capture both thermodynamics and topological order (vortex). Furthermore, we demonstrate that it is possible to extract phase transition information, including the KT transition, from the weight matrices without relying on prior physics knowledge.

In this paper, we construct two-dimensional bipartite cluster states and perform single-qubit measurements on the bulk qubits. We explore the entanglement scaling of the unmeasured one-dimensional boundary state and show that under certain conditions, the boundary state can undergo a volume-law to an area-law entanglement transition driven by variations in the measurement angle. We bridge this boundary state entanglement transition and the measurement-induced phase transition in the nonunitary ($1+1$)D circuit via the transfer matrix method. We also explore the application of this entanglement transition on the computational complexity problems. Specifically, we establish a relation between the boundary state entanglement transition and the sampling complexity of the bipartite 2D cluster state, which is directly related to the computational complexity of the corresponding Ising partition function with complex parameters. By examining the boundary state entanglement scaling, we numerically identify the parameter regime for which the 2D quantum state can be efficiently sampled, which indicates that the Ising partition function can be evaluated efficiently in such a region.

This study investigates the electronic structure of the kagome metal ${\mathrm{YbTi}}_3{\mathrm{Bi}}_4$ using high-field torque magnetometry. The torque signal measured at a maximum field of 41.5 T reveals clear de Haas–van Alphen (dHvA) oscillations with a major frequency peak at $F_{\delta }\sim$ 130 T. By rotating the sample at various tilt angles $\theta$, we observed that $F_{\delta }$ exhibits a nearly 1/$\cos \theta$ dependence, indicating the presence of a quasi-two-dimensional (2D) Fermi surface (FS) in ${\mathrm{YbTi}}_3{\mathrm{Bi}}_4$. This argument is further supported by the detection of a forward-leaning, sawtoothlike waveform in the dHvA effect, a hallmark of 2D FS characteristics. Notably, we identified two high-frequency peaks near $F_{\chi }\sim$ 1900 T and $F_{\lambda }\sim$ 5600 T; however, these peaks quickly disappear at $\theta$ greater than ${21}^{\circ }$. To better understand experimental observations, we computed the electronic band structure and FS using ab initio density-functional theory (DFT). The electronic bands reveal the presence of several Dirac points, flat bands, and van Hove singularities near the Fermi level. Five bands cross the Fermi level and contribute to the FS of this material. The FS comprises cylindrical sheets, with theoretical frequencies from the FS pockets aligning well with the experimental dHvA frequencies. Several FS parameters characterizing $F_{\delta }$ were determined by analyzing the temperature and field dependence of the dHvA oscillations using the Lifshitz-Kosevich theory. The detailed electronic properties presented in this work provide critical insights into the electronic structure of ${\mathrm{YbTi}}_3{\mathrm{Bi}}_4$ and other titanium-based kagome compounds.

We analyze heat transfer and Casimir forces involving a nonreciprocal nanoparticle. By dissecting the resulting expressions into reciprocal and nonreciprocal contributions, we find that the particle's self-emission contains $++$ and $--$ terms, i.e., the particle's reciprocal ($+$) and nonreciprocal ($-$) parts couple to the respective parts of its surrounding. In contrast, the heat transfer to the nanoparticle from the surrounding contains $-+$ and $+-$ contributions, which we find to persist at equal temperatures. For two nanoparticles, such persistent transfer is found to require one particle to be nonreciprocal and the other to be anisotropic. The propulsion force for the nanoparticle, for which our results agree with previous work, is dominated by $\pm \mp$ terms, making it distinct from forces found for reciprocal particles. The amplitude of the propulsion force can be orders of magnitude larger than gravitational forces. Despite being distinct, we find the $\pm \mp$ terms to be bound by $\pm \pm$ terms, a consequence of the passivity of the objects. For the force, this bound limits the efficiency in a heat engine setup, as observed for parallel plates before.

The effect of a magnetic scanning tunneling microscopy (STM) tip on electronic, magnetic, and electronic transport properties through the molecular junction STM-tip-Co/CoPc/Co(111) was investigated by mean of ab initio electronic structure calculations. The spin transition was studied by varying the distance (passing from the tunneling regime to the contact regime) between the tip and the CoPc molecule in both parallel and antiparallel configurations. Our calculation shows that the transition of spin of the Co atom of a CoPc molecule has led to a change of the sign of the magnetoresistance. It is also shown that the characteristic I-V has been influenced by this spin transition of the central atom of the CoPc molecule.

We carry out highly accurate ab initio path integral Monte Carlo simulations to directly estimate the free energy of various warm dense matter systems including the uniform electron gas and hydrogen without any nodal restrictions or other approximations. Since our approach is based on an effective ensemble in a bosonic configuration space, it does not increase the computational complexity beyond the usual fermion sign problem. Its application to inhomogeneous cases such as an electronic system in a fixed external ion potential is straightforward and opens up the enticing possibility to benchmark density functional theory and other existing methods. Finally, it is not limited to warm dense matter and can be applied to a gamut of other systems such as ultracold atoms and electrons in quantum dots.

Nonlinear responses in transport experiments may unveil information and generate new phenomena in materials that are not accessible at linear order due to symmetry constraints. While the linear anomalous Hall response strictly requires the absence of time-reversal symmetry, the second-order, thus nonlinear, Hall response needs broken inversion symmetry. Recently, much effort has been made to obtain a second-order Hall voltage in response to a longitudinal ac driving current, both to obtain information about band geometric quantities and for its useful technological applications, including rectification and frequency doubling. Typically, additional material engineering is required in noncentrosymmetric systems to obtain second-order responses since it obeys a stringent crystallographic symmetry constraint. To circumvent this, an alternative route is to apply a dc electric field. In this Letter, we uncover an electric field induced second-order anomalous Hall effect in inversion-broken systems possessing experimentally accessible unconventional Rashba bands. We establish that the quantum metric, a geometrical feature of electronic wave functions providing information on the nontrivial structure of Bloch bands, is responsible for providing the nonlinear Hall response.

In lattice models with quadratic finite-range Hermitian Hamiltonians, the inherently non-Hermitian transfer matrix (TM) governs the band dispersion. The van Hove singularities (VHSs) are special points in the band dispersion where the density of states (DOS) diverge. Considering a lattice chain with hopping of a finite range $n$, we find a direct fundamental connection between VHSs and exceptional points (EPs) of TM, both of arbitrary order. In particular, we show that VHSs are EPs of TM of the same order, thereby connecting two different types of critical points usually studied in widely different branches of physics. Consequently, several properties of band dispersion and VHSs can be analyzed in terms of spectral properties of TM. We further provide a general prescription to generate any order EP of the TM and therefore corresponding VHS. For a given range of hopping $n$, our analysis provides restrictions on allowed orders of EPs of TM. Finally, we exemplify all our results for the case $n=3$. Our results point to an intriguing connection between Hermitian and non-Hermitian systems.

We investigate details of the chaotic dynamics of dual-unitary quantum circuits by evaluating all $2k$-point out-of-time-ordered correlators. For the generic class of circuits, by writing the correlators as contractions of a class of quantum channels, we prove their exponential decay. This implies that local operators separated in time approach free independence. Along the way, we develop a replica trick for dual-unitary circuits, which may be useful and of interest in its own right. We classify the relevant eigenstates of the replica transfer matrix by paths in the lattice of noncrossing partitions, combinatorial objects central to free probability theory. Interestingly, the noncrossing lattice emerges even for systems without randomness and with small on-site Hilbert space dimension.

We investigate magnetic properties of the ferromagnetic Ising model on square-triangle tilings to explore how the hyperuniformity, which characterizes long-range behavior of the point pattern, influences critical phenomena where long-range correlations play a crucial role. The square-triangle tilings are spatially random structures in two dimensions constructed by densely packing the plane with squares and triangles. The growth rule with a parameter $p$ proposed in our previous paper enables systematic generations of hyperuniform, nonhyperuniform, and antihyperuniform tilings. Classical Monte Carlo simulations of the Ising model on these tilings show that critical behavior always belongs to the two-dimensional Ising universality class. It is clarified that the critical temperature is higher for the tiling with higher regularity in terms of hyperuniformity. Critical phenomena in the Ising models on the periodic and quasiperiodic tilings composed of the square and triangle tiles are also addressed.

Rare earth chalcogenides provide a great platform to study exotic quantum phenomena such as superconductivity and charge density waves. Among various interesting properties, the coupling between magnetism and electronic transport has attracted significant attention. Here, we report the investigation of such coupling in α-$\mathrm{G}{\mathrm{d}}_2\mathrm{S}{\mathrm{e}}_3$ single crystals through magnetic, calorimetric, and transport property measurements. α-$\mathrm{G}{\mathrm{d}}_2\mathrm{S}{\mathrm{e}}_3$ is found to display an antiferromagnetic ground state below 11 K with metamagnetic spin-flop transitions. The magnetic fluctuations remain strong above the transition temperature. Transport measurements reveal an overall metallic transport behavior with a large negative magnetoresistance of approximately 65% near the magnetic transition temperature, together with positive magnetoresistance near the field-induced spin-flop transitions, which can be understood in terms of the suppression of spin scattering by the magnetic field.

The critical non-Hermitian skin effect (cNHSE), first proposed in two coupled Hatano-Nelson chains, heralds a whole class of size-dependent transitions with rich anomalous scaling behaviors. Up to now, it remains unknown whether the cNHSE exists in a superconductor. This work uncovers the cNHSE in a superconducting nanowire with spin-dependent nonreciprocal hoppings. An arbitrarily small magnetic field, which couples different spins, plays a crucial role in the emergence of the cNHSE, marked by a discontinuous jump in eigenenergies and eigenstates. In finite-sized systems, the cNHSE is manifested by pronounced size-induced effects and remarkable scaling behaviors. Furthermore, applying a single strong magnetic perturbation at one end of the system can also induce the cNHSE. We observe a critical-conventional-critical NHSE transition, a direction reversal of NHSE, and the presence/absence of a Majorana zero mode by shifting the single magnetic perturbation from the left to right end of the chain. By introducing a class of quasiperiodic disorder, we investigate the interplay between cNHSE, magnetic field, and Anderson localization. This exploration reveals a rich array of localization phenomena, including distinctive localization transitions, mobility edges, and fascinating reentrant localization. Our study offers a significant proposal for realizing cNHSE in superconductors and enhances the understanding of its interplay with magnetic fields and Anderson localization.