Recent molecular photonics studies have highlighted the significant role that phase-structured light possessing orbital angular momentum (OAM) can have when interacting with matter. These studies discovered chiroptical effects sensitive to both the magnitude and sign of the optical OAM in both the absorption and scattering of twisted photons by molecules and nanoparticles. Specifically, it has been shown how a structured beam engaging with electric-quadrupole transitions in the material allows a unique sensitivity to the helical-phase structure of twisted light. In this paper we highlight experimental methodologies and systems suitable to observe and quantify the chiroptical processes of Rayleigh and Raman optical activity, and the newly discovered circular-vortex differential scattering effect with structured light—including the importance of off-axis beam alignment, input beam intensity structure, multipolar moments, and scattering-angle dependencies. It is shown that with a judicious choice of experimental setup, chiroptical effects that scale with the topological charge $\ell$ or OAM of the input beam enable optical activity signals to be enhanced and significantly exceed those based solely on circularly polarized, unstructured light. The new technique thus offers a highly useful and important spectroscopic application of structured light. The more detailed role that perfect optical vortices with high OAM will play in such optical activity effects is now highlighted, to show where there is substantial scope for experimental application, specifically in vibrational optical activity and chiral spectroscopy.

Holographic quantum error-correcting codes have been proposed as toy models that describe key aspects of the anti-de Sitter/conformal field theory (AdS/CFT) correspondence. In this work, we introduce a versatile framework of Majorana dimers capturing the intersection of stabilizer and Gaussian Majorana states. This picture allows for an efficient contraction with a simple diagrammatic interpretation and is amenable to analytical study of holographic quantum error-correcting codes. Equipped with this framework, we revisit the recently proposed hyperbolic pentagon code (HyPeC). Relating its logical code basis to Majorana dimers, we efficiently compute boundary-state properties even for the non-Gaussian case of generic logical input. The dimers characterizing these boundary states coincide with discrete bulk geodesics, leading to a geometric picture from which properties of entanglement, quantum error correction, and bulk/boundary operator mapping immediately follow. We also elaborate upon the emergence of the Ryu-Takayanagi formula from our model, which realizes many of the properties of the recent bit thread proposal. Our work thus elucidates the connection among bulk geometry, entanglement, and quantum error correction in AdS/CFT and lays the foundation for new models of holography.

Magnetization, magnetocaloric, calorimetric, neutron- and x-ray-diffraction, and inelastic-neutron-scattering measurements are performed on single crystals of $\mathrm{BaCdVO}{\left({\mathrm{PO}}_4\right)}_2$. The low-temperature crystal structure is found to be of a lower symmetry than previously assumed. The result is a more complicated model spin Hamiltonian, which we infer from measurements of the spin wave dispersion spectrum. The main finding is a spin state which emerges in high magnetic fields after antiferromagnetic order is terminated at $H_{c1}\simeq 4.0\mathrm{T}$. It is a distinct thermodynamic phase with a well-defined phase boundary at $H_{c2}\simeq 6.5\mathrm{T}$ and is clearly separate from the fully saturated phase, yet it shows no conventional (dipolar) magnetic long-range order. We argue that it is fully consistent with the expectations for a quantum bond-nematic state.

We present a far-infrared magneto-optical study of the gapped nodal-line semimetal ZrSiS in magnetic fields $B$ up to 7 T. The observed field-dependent features, which represent intra- (cyclotron resonance) and interband transitions, develop as $\sqrt{B}$ in increasing field and can be consistently explained within a simple two-dimensional Dirac band model with a gap of 26 meV and an averaged Fermi velocity of $3\times {10}^5$ m/s. This indicates a rather narrow distribution of these parameters along the in-plane portions of the nodal line in the Brillouin zone. A field-induced feature with an energy position that does not depend on $B$ is also detected in the spectra. Possible origins of this feature are discussed.

In society, mutual cooperation, defection, and exploitative relationships are common. Whereas cooperation and defection are studied extensively in the literature on game theory, exploitative relationships between players, in which one receives a larger benefit than the other while the game itself is symmetric, are little explored. In a recent seminal study, Press and Dyson demonstrated that if only one player can learn about the other, asymmetric exploitation is achieved in the prisoner's dilemma game. In their study, however, asymmetry is assumed in decision making between persons; the exploiting player one-sidedly determines and fixes the strategy and the exploited player follows it. It is unknown whether such exploitation emerges and is stably established even when both players learn about each other symmetrically and try to optimize their payoffs. Here, we first formulate a dynamical system that describes the change in a player's probabilistic strategy with reinforcement learning to obtain greater payoffs, based on the recognition of the other player. By applying this formulation to the standard prisoner's dilemma game, we numerically and analytically demonstrate that an exploitative relationship can be achieved despite symmetric strategy dynamics and symmetric rule of games. This exploitative relationship is stabilized by both the players: The exploiting player demands the other's unfair cooperation. Even though the exploited player, who receives a lower payoff than the exploiting player, has optimized the own strategy, the player accepts the other's defection to some degree. Whether the final equilibrium state is mutual cooperation, defection, or exploitation crucially depends on the initial conditions. Response to decrease the cooperation probability against a defector leads to oscillations in the probabilities of cooperation between the players and thus a complicated basin structure to the final equilibrium. In particular, any slight difference between both players' initial strategies can be amplified and fixed as a large difference in the probabilities of cooperation, leading to fixation of exploitation. In other words, symmetry breaking between the exploiting and exploited players results. Considering the generality of the result, this study provides another perspective on the origin of exploitation in society.

Band engineering in twisted bilayers of the five generic two-dimensional Bravais networks is demonstrated. We first derive constraints on the interlayer coupling that determines an effective potential for low-energy physics. The constraints are originated from symmetry and fixed without reference to microscopic details. Having the constraints on the potential helps us to predict and understand electron behavior under the influence of the moiré structure, like formation of flat bands. It is also pointed out that the generic constraints become most relevant when the typical length scale of the microscopic interlayer coupling is moderate. The concepts are numerically tested in simple tight-binding models, showing the band flattening compatible with the potential profile fixed by the generic constraints. On the basis of the generic theory, we propose a possibility of anisotropic band flattening, in which quasi-one-dimensional band dispersion is generated from relatively isotropic original band dispersion. In the strongly correlated regime, the anisotropic band flattening leads to a spin-orbital model where intertwined magnetic and orbital ordering can give rise to rich physics. Overall, our theory and demonstration give useful information for screening out interesting materials from the material database.

One of the most important tasks in modern quantum science is to coherently control and entangle many-body systems, and to subsequently use these systems to realize powerful quantum technologies such as quantum-enhanced sensors. However, many-body entangled states are difficult to prepare and preserve since internal dynamics and external noise rapidly degrade any useful entanglement. Here, we introduce a protocol that counterintuitively exploits inhomogeneities, a typical source of dephasing in a many-body system, in combination with interactions to generate metrologically useful and robust many-body entangled states. Motivated by current limitations in state-of-the-art three-dimensional (3D) optical lattice clocks (OLCs) operating at quantum degeneracy, we use local interactions in a Hubbard model with spin-orbit coupling to achieve a spin-locking effect. In addition to prolonging interparticle spin coherence, spin locking transforms the dephasing effect of spin-orbit coupling into a collective spin-squeezing process that can be further enhanced by applying a modulated drive. Our protocol is fully compatible with state-of-the-art 3D OLC interrogation schemes and may be used to improve their sensitivity, which is currently limited by the intrinsic quantum noise of independent atoms. We demonstrate that even with realistic experimental imperfections, our protocol may generate $\sim 10-14\mathrm{dB}$ of spin squeezing in $\sim 1$ second with $\sim {10}^2-{10}^4$ atoms. This capability allows OLCs to enter a new era of quantum-enhanced sensing using correlated quantum states of driven nonequilibrium systems.

We study two-dimensional spinful insulating phases of matter that are protected by time-reversal and crystalline symmetries. To characterize these phases, we employ the concept of corner charge fractionalization: corners can carry charges that are fractions of even multiples of the electric charge. The charges are quantized and topologically stable as long as all symmetries are preserved. We classify the different corner charge configurations for all point groups, and match them with the corresponding bulk topology. For this we employ symmetry indicators and (nested) Wilson loop invariants. We provide formulas that allow for a convenient calculation of the corner charge from Bloch wave functions and illustrate our results using the example of arsenic and antimony monolayers. Depending on the degree of structural buckling, these materials can exhibit two distinct obstructed atomic limits. We present density functional theory calculations for open flakes to support our findings.

In quantum information, lifting is a systematic procedure that can be used to derive—when provided with a seed Bell inequality—other Bell inequalities applicable in more complicated Bell scenarios. It is known that the procedure of lifting introduced by Pironio [J. Math. Phys. 46, 062112 (2005)] preserves the facet-defining property of a Bell inequality. Lifted Bell inequalities therefore represent a broad class of Bell inequalities that can be found in all Bell scenarios. Here, we show that the maximal value of any lifted Bell inequality is preserved for both the set of nonsignaling correlations and quantum correlations. Despite the degeneracy in the maximizers of such inequalities, we show that the ability to self-test a quantum state is preserved under these lifting operations. In addition, except for outcome lifting, local measurements that are self-testable using the original Bell inequality—despite the degeneracy—can also be self-tested using any lifted Bell inequality derived therefrom. While it is not possible to self-test all the positive-operator-valued measure elements using an outcome-lifted Bell inequality, we show that partial, but robust self-testing statements on the underlying measurements can nonetheless be made from the quantum violation of these lifted inequalities. We also highlight the implication of our observations on the usefulness of using lifted Bell-like inequalities as a device-independent witnesses for entanglement depth. The impact of the aforementioned degeneracy on the geometry of the quantum set of correlations is briefly discussed.

Twisted bilayer graphene (TBLG) has emerged as an important platform for studying correlated phenomena, including unconventional superconductivity, in two-dimensional systems. The complexity of the atomic-scale structures in TBLG has made even the study of single-particle physics at low energies around the Fermi level, quite challenging. Our goal here is to provide a convenient and physically motivated picture of single-particle physics in TBLG using reduced models with the smallest possible number of localized orbitals. The reduced models exactly reproduce the low-energy bands of ab initio tight-binding models, including the effects of atomic relaxations. Furthermore, we obtain for the first time the corresponding Wannier orbitals that incorporate all symmetries of TBLG, which are also calculated as a function of angle, a requisite first step towards incorporating electron interaction effects. We construct eight-band and five-band models for the low-energy states for twist angles between $1.3^{\circ }$ and $0.6^{\circ }$. The models are created using a multistep Wannier projection technique starting with appropriate ab initio $\mathit{k}·\mathit{p}$ continuum Hamiltonians. Our procedure can also readily capture the perturbative effects of substrates and external displacement fields while offering a significant reduction in complexity for studying electron-electron correlation phenomena in realistic situations.

We formulate a quantum theory of vorticity (hydro)dynamics on a general two-dimensional bosonic lattice. In the classical limit of a bosonic condensate, it reduces to conserved plasma-like vortex-antivortex dynamics. The nonlocal topological character of the vorticity flows is reflected in the bulk-edge correspondence dictated by the Stokes theorem. This is exploited to establish physical boundary conditions that realize, in the coarse-grained thermodynamic limit, an effective chemical-potential bias of vorticity. A Kubo formula is derived for the vorticity conductivity, which could be measured in a suggested practical device, in terms of quantum vorticity-flux correlators of the original lattice model. As an illustrative example, we discuss the superfluidity of vorticity, exploiting the particle-vortex duality at a bosonic superfluid-insulator transition.

We observe a series of unstable and dynamic behaviors of acoustic vortices propagating in stratified inhomogeneous media. These behaviors include bending, stretching, distorting, focusing, and untwisting of the vortices, migration of singular points, and reversal of energy flux and angular momentum. We gain insight into how these behaviors result from the stratification. The results will be useful for applications of acoustic vortices in communication and particle manipulations in inhomogeneous media such as oceans and biomedical tissues. Our work opens up the study of the propagation of acoustic vortices in complex media.

We study the single-particle spectrum of three-dimensional Weyl semimetals taking into account electron-phonon interactions that are the result of straining the material. We find that a well-defined fermionic excitation appears in addition to the standard peak corresponding to quasiparticle states as suggested by Landau-Fermi liquid theory. Contrary to the case of Dirac systems interacting via the Coulomb interaction, these satellite peaks appear even at lowest order in perturbation theory. The new excitations are anisotropic, as opposed to the single-particle spectrum, and their behavior is dictated by the Debye frequency, which naturally regulates the electron-phonon coupling.

It is well known that an interface created by two topologically distinct structures could host nontrivial edge states that are immune to defects. In this paper, we introduce a one-dimensional space-time phononic crystal and study the associated anomalous topological edge states when the phononic crystal's density is modulated both in space and time. While preserving the key topological feature of the system, the time modulation also duplicates the edge state mode across the spectrum, both inside and outside the band gap. It is shown that, in contrast to conventional topological edge states which are excited by frequencies in the Bragg regime, the time-modulation-induced frequency conversion can be leveraged to access topological edge states at a deep subwavelength scale where the entire phononic crystal size can be as small as 1/5.1 of the wavelength. This feature could open another route for designing miniature devices that are based on topological physics.

We investigate the generation and propagation characteristics of leaky Rayleigh waves (LRWs) caused by a spherical shock wave incident on a water-glass boundary both experimentally and numerically. The maximum tensile stress produced on the solid boundary is attributed to the dynamic interaction between the LRWs and an evanescent wave generated concomitantly along the boundary. The resultant tensile stress field drives the initiation of crack formation from pre-existing surface flaws and their subsequent extension along a circular trajectory, confirmative with the direction of the principal stress on the boundary. We further demonstrate that this unique ringlike fracture pattern, prevalent in damage produced by high-speed impact, can be best described by the Tuler-Butcher criterion for dynamic failure in brittle materials. The orientation of the ring fracture extension into the solid also follows closely with the trajectory of the local maximum tensile stress distribution.

Generic quantum many-body systems typically show a linear growth of the entanglement entropy after a quench from a product state. While entanglement is a property of the wave function, it is generated by the unitary time-evolution operator and is therefore reflected in its increasing complexity as quantified by the operator entanglement entropy. Using numerical simulations of a static and a periodically driven quantum spin chain, we show that there is a robust correspondence between the entanglement entropy growth of typical product states and the operator entanglement entropy of the unitary evolution operator, while special product states, e.g., ${\sigma }_z$ basis states, can exhibit faster entanglement production. In the presence of a disordered magnetic field in our spin chains, we show that both the wave function and operator entanglement entropies exhibit a power-law growth with the same disorder-dependent exponent and clarify the apparent discrepancy in previous results. These systems, in the absence of conserved densities, provide further evidence for slow information spreading on the ergodic side of the many-body localization transition.

We consider a Floquet triple-layer setup composed of a two-dimensional electron gas with spin-orbit interactions, proximity coupled to an $s$-wave superconductor and to a ferromagnet driven at resonance. The ferromagnetic layer generates a time-oscillating Zeeman field which competes with the induced superconducting gap and leads to a topological phase transition. The resulting Floquet states support a second-order topological superconducting phase with a pair of localized zero-energy Floquet Majorana corner states. Moreover, the phase diagram comprises a Floquet helical topological superconductor, hosting a Kramers pair of Majorana edge modes protected by an effective time-reversal symmetry, as well as a gapless Floquet Weyl phase. The topological phases are stable against disorder as well as against parameter variations and are within experimental reach.

We report a computer simulation study of the phase transitional behavior of a system of chiral Gay-Berne molecules embedded with a terminal dipole. In this Rapid Communication, coarse-grained modeling is done to study the influence of coupled chiral and dipolar interactions on the macroscopic liquid crystalline phase behavior. This $NVT$ molecular dynamics simulation study presents the formation of the smectic blue phase (${\mathrm{BP}}_{\mathrm{Sm}}$), which is a comparatively recent experimentally discovered chiral phase. Our study reveals that a gradual increment of the strength of the chiral interaction brings conventional cholesteric and blue phases, whereas the addition of a dipolar interaction can induce the smectic blue phase. Moreover, we demonstrate that a further increase of dipolar strength makes novel chiral bilayer phases feasible, yet to be realized experimentally.

Two- and three-dimensional Kitaev magnets are prototypical frustrated quantum spin systems, in which the original spin degrees of freedom fractionalize into Majorana fermions and a ${\mathbb{Z}}_2$ gauge field—a purely local phenomenon that reveals itself as a thermodynamic crossover at a temperature scale set by the strength of the bond-directional interactions. For conventional Kitaev magnets, the low-temperature thermodynamics reveals a second transition at which the ${\mathbb{Z}}_2$ gauge field orders and the system enters a spin-liquid ground state. Here, we discuss an explicit example that goes beyond this paradigmatic scenario—the ${\mathbb{Z}}_2$ gauge field is found to be subject to geometric frustration, the thermal ordering transition is suppressed, and an extensive residual entropy arises. Deep in the quantum regime, at temperatures of the order of one per mil of the interaction strength, the degeneracy in the gauge sector is lifted by a subtle interplay between the gauge field and the Majorana fermions, resulting in the formation of a Majorana metal. We discuss the thermodynamic signatures of this physics obtained from large-scale, sign-free quantum Monte Carlo simulations.

We consider an autonomous implementation of Maxwell's demon in a quantum dot architecture acting on a system without changing its number of particles or its energy. As in the original thought experiment, only the second law of thermodynamics is seemingly violated when disregarding the demon. The autonomous architecture allows us to compare descriptions in terms of information to a more traditional, thermoelectric characterization. Our detailed investigation of information-to-work conversion is based on fluctuation relations and second-law-like inequalities in addition to the average heat and charge currents. By introducing a time reversal on the level of individual electrons, we find a fluctuation relation that is not connected to any symmetry of the moment-generating function of heat and particle flows. Furthermore, we show how an effective Markovian master equation with broken detailed balance for the system alone can emerge from a full description, allowing for an investigation of the entropic cost associated with breaking detailed balance. Interestingly, while the entropic cost of performing a perfect measurement diverges, the entropic cost of breaking detailed balance does not. Our results connect various approaches and idealized scenarios found in the literature and can be tested experimentally with present-day technology.