Three modified sine-Hilbert (sH)-type equations, i.e., the modified sH equation, the modified damped sH equation, and the modified nonlinear dissipative system, are proposed, and their bilinear forms are provided. Based on these bilinear equations, some exact solutions to the three modified equations are derived.

Adiabatic time-optimal quantum controls are extensively used in quantum technologies to break the constraints imposed by short coherence times. However, practically it is crucial to consider the trade-off between the quantum evolution speed and instantaneous energy cost of process because of the constraints in the available control Hamiltonian. Here, we experimentally show that using a transmon qubit that, even in the presence of vanishing energy gaps, it is possible to reach a highly time-optimal adiabatic quantum driving at low energy cost in the whole evolution process. This validates the recently derived general solution of the quantum Zermelo navigation problem, paving the way for energy-efficient quantum control which is usually overlooked in conventional speed-up schemes, including the well-known counter-diabatic driving. By designing the control Hamiltonian based on the quantum speed limit bound quantified by the changing rate of phase in the interaction picture, we reveal the relationship between the quantum speed limit and instantaneous energy cost. Consequently, we demonstrate fast and high-fidelity quantum adiabatic processes by employing energy-efficient driving strengths, indicating a promising strategy for expanding the applications of time-optimal quantum controls in superconducting quantum circuits.

Non-Hermitian Hamiltonians are widely used in describing open systems with gain and loss, among which a key phenomenon is the non-Hermitian skin effect. Here we report an experimental scheme to realize a two-dimensional (2D) discrete-time quantum walk with non-Hermitian skin effect in a single trapped ion. It is shown that the coin and 2D walker states can be labeled in the spin of the ion and the coherent-state lattice of the ion motion, respectively. We numerically observe a directional bulk flow, whose orientations are controlled by dissipative parameters, showing the emergence of the non-Hermitian skin effect. We then discuss an experimental implementation of our scheme in a laser-controlled trapped Ca$^{+}$ ion. Our experimental proposal may be applicable to research of dissipative quantum walk systems and may be able to generalize to other platforms, such as superconducting circuits and atoms in cavity.

Quantum gates are crucial for quantum computation and quantum information processing. However, their effectiveness is often hindered by systematic errors and decoherence. Therefore, achieving resilient quantum gates to these factors is of great significance. We present a method to construct nonadiabatic holonomic single- and two-qubit gates in a Rydberg ground-state-blockade regime. Our approach utilizes a far-off-resonant technique for the single-qubit gate and a modified Rydberg antiblockade for the two-qubit gate. The reduction of the population of single- and two-excitation Rydberg states and the nonadiabatic holonomic process during the construction of the gates ensure robustness to decoherence and systematic errors, respectively. Numerical results demonstrate the fidelity and robustness of our scheme. The proposed scheme holds promise for future applications in quantum computation and quantum information processing tasks.

We study dark localized waves within a nonlinear system based on the Boussinesq approximation, describing the dynamics of shallow water waves. Employing symbolic calculus, we apply the Hirota bilinear method to transform an extended Boussinesq system into a bilinear form, and then use the multiple rogue wave method to obtain its dark rational solutions. Exploring the first- and second-order dark solutions, we examine the conditions under which these localized solutions exist and their spatiotemporal distributions. Through the selection of various parameters and by utilizing different visualization techniques (intensity distributions and contour plots), we explore the dynamical properties of dark solutions found: in particular, the first- and second-order dark rogue waves. We also explore the methods of their control. The findings presented here not only deepen the understanding of physical phenomena described by the (1$+$1)-dimensional Boussinesq equation, but also expand avenues for further research. Our method can be extended to other nonlinear systems, to conceivably obtain higher-order dark rogue waves.

A high-performance adaptive radiative cooler comprising a multilayer-filter VO$_{2}$-based Fabry–Pérot (FP) cavity is proposed. The bottom FP cavity has four layers, VO$_{2}$/NaCl/PVC/Ag. Based on the phase transition of VO$_{2}$, the average emissivity in the transparent window can be switched from 3.7% to 96.3%. Additionally, the average emissivity can also be adjusted with external strain to the PVC layer, providing another way to attain the desired cooling effect. An upper filter is included to block most of the solar radiation and provide a transmittance of 96.7% in the atmospheric window. At high temperature, the adaptive emitter automatically activates radiative cooling. The net cooling power is up to 156.4 W$\cdot $m$^{-2}$ at an ambient temperature of 303 K. Our adaptive emitter still exhibits stable selective emissivity at different incident angles and heat transfer coefficients. At low temperature, the radiative cooling automatically deactivates, and the average emissivity decreases to only 3.8%. Therefore, our work not only provides new insights into the design of high-performance adaptive radiative coolers but also advances the development of intelligent thermal management.

Using THz emission spectroscopy, we investigate the elementary spin dynamics in ferromagnetic single-layer Fe on a sub-picosecond timescale. We demonstrate that THz radiation changes its polarity with reversal of the magnetization applied by the external magnetic field. In addition, it is found that the sign of THz polarity excited from different sides is defined by the thickness of the Fe layer and Fe/dielectric interface. Based on the thickness and symmetry dependences of THz emission, we experimentally distinguish between the two major contributions: ultrafast demagnetization and the anomalous Hall effect. Our experimental results not only enrich understanding of THz electromagnetic generation induced by femtosecond laser pulses but also provide a practical way to access laser-induced ultrafast spin dynamics in magnetic structures.

As a key component in all-optical networks, all-optical switches play a role in constructing all-optical switching. Due to the absence of photoelectric conversion, all-optical networks can overcome the constraints of electronic bottlenecks, thereby improving communication speed and expanding their communication bandwidth. We study all-optical switches based on the interactions among three optical solitons. By analytically solving the coupled nonlinear Schrödinger equation, we obtain the three-soliton solution to the equation. We discuss the nonlinear dynamic characteristics of various optical solitons under different initial conditions. Meanwhile, we analyze the influence of relevant physical parameters on the realization of all-optical switching function during the process of three-soliton interactions. The relevant conclusions will be beneficial for expanding network bandwidth and reducing power consumption to meet the growing demand for bandwidth and traffic.

Nonreciprocal optical devices are essential for laser protection, modern optical communication and quantum information processing by enforcing one-way light propagation. The conventional Faraday magneto-optical nonreciprocal devices rely on a strong magnetic field, which is provided by a permanent magnet. As a result, the isolation direction of such devices is fixed and severely restricts their applications in quantum networks. In this work, we experimentally demonstrate the simultaneous one-way transmission and unidirectional reflection by using a magneto-optical Fabry–Pérot cavity and a magnetic field strength of 50 mT. An optical isolator and a three-port quasi-circulator are realized based on this nonreciprocal cavity system. The isolator achieves an isolation ratio of up to 22 dB and an averaged insertion loss down to 0.97 dB. The quasi-circulator is realized with a fidelity exceeding $99\%$ and an overall survival probability of $89.9\%$, corresponding to an insertion loss of $\sim$ $0.46$ dB. The magnetic field is provided by an electromagnetic coil, thereby allowing for reversing the light circulating path. The reversible quasi-circulator paves the way for building reconfigurable quantum networks.

A Moiré system is formed when two periodic structures have a slightly mismatched period, resulting in unusual strongly correlated states in the presence of particle-particle interactions. The periodic structures can arise from the intrinsic crystalline order and periodic external field. We investigate a one-dimensional Hubbard model with periodic on-site potential of period $n_{0}$, which is commensurate to the lattice constant. For large $n_{0}$, the exact solution demonstrates that there is a midgap flat band with zero energy in the absence of Hubbard interaction. Each Moiré unit cell contributes two zero energy levels to the flat band. In the presence of Hubbard interaction, the midgap physics is demonstrated to be well described by a uniform Hubbard chain in which the effective hopping and on-site interaction strength can be controlled by the amplitude and period of the external field. Numerical simulations are performed to demonstrate the correlated behaviors in the finite-sized Moiré Hubbard system, including the existence of an $\eta $-pairing state and bound pair oscillation. This finding provides a method to enhance the correlated effect by a spatially periodic external field.

Floquet engineering has attracted considerable attention as a promising approach for tuning topological phase transitions. We investigate the effects of high-frequency time-periodic driving in a four-dimensional (4D) topological insulator, focusing on topological phase transitions at the off-resonant quasienergy gap. The 4D topological insulator hosts gapless three-dimensional boundary states, characterized by the second Chern number $C_{2}$. We demonstrate that the second Chern number of 4D topological insulators can be modulated by tuning the amplitude of time-periodic driving. This includes transitions from a topological phase with $C_{2}=\pm3$ to another topological phase with $C_{2}=\pm1$, or to a topological phase with an even second Chern number $C_{2}=\pm2$, which is absent in the 4D static system. Finally, the approximation theory in the high-frequency limit further confirms the numerical conclusions.

We theoretically study the charge order and orbital magnetic properties of a new type of antiferromagnetic kagome metal FeGe. Based on first-principles density functional theory calculations, we study the electronic structures, Fermi-surface quantum fluctuations, as well as phonon properties of the antiferromagnetic kagome metal FeGe. It is found that charge density wave emerges in such a system due to a subtle cooperation between electron–electron interactions and electron–phonon couplings, which gives rise to an unusual scenario of interaction-triggered phonon instabilities, and eventually yields a charge density wave (CDW) state. We further show that, in the CDW phase, the ground-state current density distribution exhibits an intriguing star-of-David pattern, leading to flux density modulation. The orbital fluxes (or current loops) in this system emerge as a result of the subtle interplay between magnetism, lattice geometries, charge order, and spin-orbit coupling (SOC), which can be described by a simple, yet universal, tight-binding theory including a Kane–Mele-type SOC term and a magnetic exchange interaction. We further study the origin of the peculiar step-edge states in FeGe, which sheds light on the topological properties and correlation effects in this new type of kagome antiferromagnetic material.

Surface acoustic wave (SAW) is a powerful technique for investigating quantum phases appearing in two-dimensional electron systems. The electrons respond to the piezoelectric field of SAW through screening, attenuating its amplitude, and shifting its velocity, which is described by the relaxation model. In this work, we systematically study this interaction using orders of magnitude lower SAW amplitude than those in previous studies. At high magnetic fields, when electrons form highly correlated states such as the quantum Hall effect, we observe an anomalously large attenuation of SAW, while the acoustic speed remains considerably high, inconsistent with the conventional relaxation model. This anomaly exists only when the SAW power is sufficiently low.

What factors fundamentally determine the value of superconducting transition temperature $T_{\rm c}$ in high temperature superconductors has been the subject of intense debate. Following the establishment of an empirical law known as Homes' law, there is a growing consensus in the community that the $T_{\rm c}$ value of the cuprate superconductors is closely linked to the superfluid density ($\rho_{\rm s}$) of its ground state and the conductivity ($\sigma $) of its normal state. However, all the data supporting this empirical law ($\rho_{\rm s} = A\sigma T_{\rm c}$) have been obtained from the ambient-pressure superconductors. In this study, we present the first high-pressure results about the connection of the quantities of $\rho_{\rm s}$ and $\sigma $ with $T_{\rm c}$, through the studies on the Bi$_{1.74}$Pb$_{0.38}$Sr$_{1.88}$CuO$_{6+\delta }$ and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$, in which the value of their high-pressure resistivity ($\rho =1/\sigma $) is achieved by adopting our newly established method, while the quantity of $\rho_{\rm s}$ is extracted using Homes' law. We highlight that the $T_{\rm c}$ values are strongly linked to the joint response factors of magnetic field and electric field, i.e., $\rho_{\rm s}$ and $\sigma $, respectively, implying that the physics determining $T_{\rm c} $ is governed by the intrinsic electromagnetic fields of the system.

We report on soft $c$-axis point-contact Andreev reflection (PCAR) spectroscopy combining with resistivity measurements on BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$, to elucidate the superconducting gap structure in the vicinity of the quantum critical point. A double peak at the gap edge plus a dip feature at zero-bias has been observed on the PCAR spectra, indicative of the presence of a nodeless gap in BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$. Detailed analysis within a sophisticated theoretical model reveals an anisotropic gap with deep gap minima. The PCARs also feature additional structures related to the electron–bosonic coupling mode. Using the extracted superconducting energy gap value, a characteristic bosonic energy $\varOmega_{\rm b}$ and its temperature dependence are obtained, comparable with the spin-resonance energy observed in neutron scattering experiment. These results indicate a magnetism-driven quantum critical point in the BaFe$_2$(As$_{1-x}$P$_x$)$_2$ system.

Two-dimensional (2D) van der Waals magnetic materials have promising and versatile electronic and magnetic properties in the 2D limit, indicating a considerable potential to advance spintronic applications. Theoretical predictions thus far have not ascertained whether monolayer VCl$_{3}$ is a ferromagnetic (FM) or anti-FM monolayer; this also remains to be experimentally verified. We theoretically investigate the influence of potential factors, including $C_{3}$ symmetry breaking, orbital ordering, epitaxial strain, and charge doping, on the magnetic ground state. Utilizing first-principles calculations, we predict a collinear type-III FM ground state in monolayer VCl$_{3}$ with a broken $C_{3}$ symmetry, wherein only the former two of three $t_{\rm 2g}$ orbitals ($a_{\rm 1g}$, $e^{\pi}_{\rm g2}$ and $e^{\pi}_{\rm g1}$) are occupied. The atomic layer thickness and bond angles of monolayer VCl$_{3}$ undergo abrupt changes driven by an orbital ordering switch, resulting in concomitant structural and magnetic phase transitions. Introducing doping to the underlying Cl atoms of monolayer VCl$_{3}$ without $C_{3}$ symmetry simultaneously induces in- and out-of-plane polarizations. This can achieve a multiferroic phase transition if combined with the discovered adjustments of magnetic ground state and polarization magnitude under strain. The establishment of an orbital-ordering driven regulatory mechanism can facilitate deeper exploration and comprehension of magnetic properties of strongly correlated systems in monolayer VCl$_{3}$.

In comparison to ferromagnets, antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices, including fast spin dynamics, vanishing stray fields and robust against external magnetic field, etc. However, unlike ferromagnetic orders, which could be detected through tunneling magnetoresistance effect in magnetic tunnel junctions, the antiferromagnetic order (i.e., Néel vector) cannot be effectively detected by the similar mechanism due to the spin degeneracy of conventional antiferromagnets. Recently discovered spin-splitting noncollinear antiferromagnets, such as Mn$_{3}$Pt with momentum-dependent spin polarization due to their special magnetic space group, make it possible to achieve remarkable tunneling magnetoresistance effects in noncollinear antiferromagnetic tunnel junctions. Through first-principles calculations, we demonstrate that the tunneling magnetoresistance ratio can reach more than 800% in Mn$_{3}$Pt/perovskite oxides/Mn$_{3}$Pt antiferromagnetic tunnel junctions. We also reveal the switching dynamics of Mn$_{3}$Pt thin film under magnetic fields using atomistic spin dynamic simulation. Our study provides a reliable method for detecting Néel vector of noncollinear antiferromagnets through the tunnel magnetoresistance effect and may pave its way for potential applications in antiferromagnetic memory devices.

Exploration of exotic phenomena in magnetic topological systems is at the frontier of condensed matter physics, holding a significant promise for applications in topological spintronics. However, complex magnetic structures carrying nontrivial topological properties hinder its progresses. Here, we investigate the pressure effect on the novel topological kagome magnets GdV$_{6}$Sn$_{6}$ and TbV$_{6}$Sn$_{6}$ to dig out the interplay between magnetic Gd/Tb layers and nonmagnetic V-based kagome sublattice. The pressure-tuned magnetic transition temperature $T_{\rm m}$ in both the compounds exhibit a turning point at the critical pressure $P_{\rm c}$, accompanied with a sign reversal in anomalous Hall effect (AHE). The separation of intrinsic and extrinsic contributions using the Tian–Ye–Jin scaling model suggests that the intrinsic mechanism originating from the electronic Berry curvature holds the priority in the competition with extrinsic mechanism in AHE. The above-mentioned findings can be attributed to the combined effect of pressure-tuned band topology and magnetic interaction in segregated layers. Our results provide a practical route to design and manipulate the intrinsic AHE in magnetic topological materials.

Phase transitions involving oxygen ion extraction within the framework of the crystallographic relevance have been widely exploited for sake of superconductivity, ferromagnetism, and ion conductivity in perovskite-related oxides. However, atomic-scale pathways of phase transitions and ion extraction threshold are inadequately understood. Here we investigate the atomic structure evolution of LaCoO$_{3}$ films upon oxygen extraction and subsequent Co migration, focusing on the key role of epitaxial strain. The brownmillerite to Ruddlesden–Popper phase transitions are discovered to stabilize at distinct crystal orientations in compressive- and tensile-strained cobaltites, which could be attributed to in-plane and out-of-plane Ruddlesden–Popper stacking faults, respectively. A two-stage process from exterior to interior phase transition is evidenced in compressive-strained LaCoO$_{2.5}$, while a single-step nucleation process leaving bottom layer unchanged in tensile-strained situation. Strain analyses reveal that the former process is initiated by an expansion in Co layer at boundary, whereas the latter one is associated with an edge dislocation combined with antiphase boundary. These findings provide a chemo-mechanical perspective on the structure regulation of perovskite oxides and enrich insights into strain-dependent phase diagram in epitaxial oxides films.

Novel electron states stabilized by Coulomb interactions attract tremendous interests in condensed matter physics. These states are studied by corresponding phase transitions occurring at extreme conditions such as mK temperatures and high magnetic field. In this work, we introduce a magneto-optical Kerr effect measurement system to comprehensively explore these phases in addition to conventional transport measurement. This system, composed of an all-fiber zero-loop Sagnac interferometer and in situ piezo-scanner inside a dilution refrigerator, operates below 100 mK, with a maximum field of 12 Tesla and has a resolution as small as 0.2 µrad. As a demonstration, we investigate TbMn$_6{\rm Sn}_6$, where the manganese atoms form Kagome lattice that hosts topological non-trivial Dirac cones. We observed two types of Kerr signals, stemming from its fully polarized ferromagnetic ground state and positive charged carriers within the Dirac-like dispersion.

Ba$_{6}$Cr$_{2}$S$_{10}$ is a recently discovered magnetic material, in which the spins are aligned ferromagnetically in the ab-plane and anti-parallelly in a paired form along the $c$-axis. It is characterized as a quasi-one dimensional (1D) dimerized structure with a ferrotoroidic order, forming the simplest candidate toroidal magnetic (TM) order and exhibiting an anti-ferromagnetic-like transition at around 10 K. Time-resolved ultrafast dynamics investigation of the novel A–Cr–S (A: metal elements) family of quantum materials has rarely been reported. Here, we investigate the time-resolved pump-probe ultrafast dynamics of a Ba$_{6}$Cr$_{2}$S$_{10}$ single crystal. A prominent change in the photo-excited carrier dynamics is observed at $T_{\rm c}=10$ K, corresponding to the reported TM-paramagnetic phase transition. A potential unknown magnetic transition is also found at $T^{*}=29$ K. Our results provide new evidence for the TM magnetic transition in Ba$_{6}$Cr$_{2}$S$_{10}$, and shed light on phase transitions in TM quantum materials.

Probing the energy band gap of solid nitrogen at high pressures is of importance for understanding pressure-driven changes in electronic structures and insulator-to-metal transitions under high pressure. The $\lambda $-N$_{2}$ formed by cold compression is known to be the most stable one in all solid nitrogen phases observed so far. By optimizing the optical system, we successfully measured the high-pressure absorption spectra of $\lambda $-N$_{2}$ covering the polymeric-nitrogen synthetic pressures (124 GPa–165 GPa). The measured optical band gap decreases with increasing pressure, from 2.23 eV at 124 GPa to 1.55 eV at 165 GPa, with a negative pressure coefficient of $-18.4$ meV/GPa, which is consistent with the result from our ab initio total-energy calculations ($-22.6 $ meV/GPa). The extrapolative metallization pressure for the $\lambda $-N$_{2}$ is around 288(18) GPa, which is close to the metallization pressure (280 GPa) for the $\eta $-N$_{2}$ expected by previous absorption edge and direct electrical measurements. Our results provide a direct spectroscopic evidence for the pressure-driven band gap narrowing of solid nitrogen.