We introduce a framework to distinguish long-range quantum entanglement from long-range classical correlations close to a finite temperature critical point in a quantum system. In particular, we employ “tripartite entanglement negativity,” a mixed-state entanglement measure, to cancel out critical correlations that are purely classical in origin. As an application, we study an exactly solvable model, and find that the tripartite negativity does not exhibit any singularity in the thermodynamic limit across the transition. This indicates that the long-distance critical fluctuations are completely classical, and it allows one to define a “quantum correlation length” that remains finite at the transition despite a divergent physical correlation length. Motivated by our model, we also study mixed-state entanglement in tight-binding models of bosons with $\text{U}\left(1\right)$ and time-reversal symmetries. By employing Glauber-Sudarshan representation, we find a surprising result that such states have zero entanglement.

We analyze the robustness of corner modes in topological photonic crystals, taking a $C_6$-symmetric breathing honeycomb photonic crystal as an example. First, we employ topological quantum chemistry and Wilson loop calculations to demonstrate that the topological properties of the bulk crystal stem from an obstructed atomic limit phase. We then characterize the topological corner modes emerging within the gapped edge modes employing a semianalytical model, determining the appropriate real-space topological invariants. We provide a detailed account of the effect of long-range interactions on the topological modes in photonic crystals, and we quantify their robustness to perturbations. We conclude that, while photonic long-range interactions inevitably break chiral symmetry, the system is reducible to a chirally symmetric limit and the corner modes are protected by this together with lattice symmetries.

The evolution of magnetic polarons in Sr doped $\mathrm{La}\mathrm{Co}{\mathrm{O}}_3$ (${\mathrm{La}}_{1\text{−}x}{\mathrm{Sr}}_x\mathrm{Co}{\mathrm{O}}_3$) single crystal and polycrystalline samples are investigated by employing dc and ac magnetic measurement and small angle neutron scattering (SANS) techniques. The effect of magnetic field and temperature on magnetic polarons is experimentally studied for ${\mathrm{La}}_{0.875}{\mathrm{Sr}}_{0.125}\mathrm{Co}{\mathrm{O}}_3$ and ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}\mathrm{Co}{\mathrm{O}}_3$ compounds that belong to the spin glass insulating regime of the broader compositional phase diagram of this system. Langevin analyses of the isothermal magnetization curves in the notional paramagnetic regime prove the existence of magnetic polarons with large moments. The dc field superimposed ac susceptibility data and the analysis of the glassy dynamics prove that the size of polarons in 15% Sr doped crystal increase as the field is increased while the field effect is not visible in the 12.5% Sr doped crystal. A polycrystalline sample of ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}\mathrm{Co}{\mathrm{O}}_3$ is analyzed by SANS experiments, which confirm nonzero correlation length at temperatures far above the macroscopic ordering temperature and hence the presence of magnetic polarons.

We study how translationally invariant couplings between many-particle systems and nonequilibrium baths can be used to rectify particle currents, for which we consider minimal setups to realize bath-induced currents in nonequilibrium steady states of one-dimensional open fermionic systems. We first analyze dissipative dynamics associated with a nonreciprocal Lindblad operator and identify a class of Lindblad operators that are sufficient to acquire a unidirectional current. We show that unidirectional particle transport can, in general, occur when a Lindblad operator is reciprocal provided that the inversion symmetry and the time-reversal symmetry of the microscopic Hamiltonian are broken. We demonstrate this mechanism on the basis of both analytical and numerical approaches, including the Rashba spin-orbit coupling and the Zeeman magnetic field.

The connection between fundamental nucleon-nucleon forces and the observed many-body structure of nuclei is a main question of modern nuclear physics. Evolution of the mean field, inversion of traditional shell structures, and structure of high spin states in nuclei with extreme proton-to-neutron ratios are at the center of numerous recent experimental investigations targeting the matrix elements of the effective nuclear Hamiltonian that is responsible for these phenomena. The FSU $spsdfp$ cross-shell interaction for the shell model was successfully fitted to a wide range of mostly intruder negative parity states of the $sd$ shell nuclei. In this paper, we explore the evolution of nuclear structure in and around the island of inversion (IoI), where low-lying states involve cross-shell particle-hole excitations. We apply the FSU interaction to systematically trace out the relative positions of the effective single-particle energies of the $0f_{7/2}$ and $1p_{3/2}$ orbitals forming the $N=20$ and 28 shell gaps. We find that above a proton number of about 13, the $0f_{7/2}$ neutron orbital lies below that of $1p_{3/2}$, which is considered normal ordering but, systematically, for more exotic nuclei with lower $Z=12$ and 10 the order of orbitals reversed. The crossing of the neutron orbitals happens right near the neutron separation threshold. Our Hamiltonian reproduces remarkably well the absolute binding energies for a broad range of nuclei and the inversion in the configurations of nuclei inside the IoI. The effective interaction accounts well for the energies and variations with mass number $A$ of aligned high-spin states that involve nucleon pairs prompted across the shell gap. This paper puts forward an empirically determined effective Hamiltonian where data from many recent experiments allowed us to significantly improve our knowledge about cross-shell nuclear interaction matrix elements. The quality with which this Hamiltonian describes the two-particle, two-hole cross-shell excitations, binding energies, and the physics of aligned states that were not a part of the fit, is remarkable, making the FSU interaction an important tool for the future exploration of exotic nuclei.

The emission of high-energy photons is one of the major effects of relativistic laser-plasma interactions, which underpins a wide range of applications, from plasma diagnostics to radiography to nuclear physics and quantum electrodynamics studies. In the case of solid targets, such emission is usually dominated by Bremsstrahlung and radiative transitions of excited ions, yet one expects prolific synchrotron emission to kick in and eventually prevail at high enough laser intensities, such as those contemplated at various facilities under construction worldwide. In this paper, by means of advanced, self-consistent particle-in-cell numerical simulations, we present a detailed analysis of x-ray and $\gamma$-ray radiation under previously unexplored interaction conditions, involving ultrathin targets partially transparent to the laser light, yet accessible to multipetawatt laser systems during their early operation phase. We first examine the characteristics of synchrotron radiation from laser-driven plasmas of varying density and size. In particular, we show and explain the dependence of the angular distribution of the radiated photons on the transparency or opacity of the plasma. We then study the competition of the synchrotron and Bremsstrahlung emissions in copper foil targets irradiated with ${10}^{22}\mathrm{W}{\mathrm{cm}}^{-2}$, 50-fs laser pulses. Synchrotron emission is observed to be maximized for target thicknesses of a few tens of nanometers, close to the relativistic transparency threshold, and to be superseded by Bremsstrahlung in targets a few microns thick. At their best efficiency, both mechanisms are found to radiate about 1% of the laser energy into photons with energies above 10 keV. Their energy and angular spectra are thoroughly analyzed in light of the ultrafast target expansion, the influence of which has been overlooked so far. Our results demonstrate that even using solid materials of relatively high atomic number and not-so-extreme laser pulse intensities, synchrotron radiation can be a strongly dominant and efficient source of energetic photons provided the targets are thin enough.

Activating transitions between a set of atomic internal states has emerged as an elegant scheme by which lattice models can be designed in ultracold atomic gases. In this approach, the internal states can be viewed as fictitious lattice sites defined along a synthetic dimension, hence offering a powerful method by which the spatial dimensionality of the system can be extended. Interparticle collisions generically lead to infinite-range interactions along the synthetic dimensions, which a priori precludes the design of Bose-Hubbard-type models featuring on-site interactions. In this paper, we solve this obstacle by introducing a protocol that realizes strong and tunable “on-site” interactions along an atomic synthetic dimension. Our scheme is based on pulsing strong intraspin interactions in a fast and periodic manner, hence realizing the desired on-site interactions in a digital (Trotterized) manner. We explore the viability of this protocol by means of numerical calculations, which we perform on various examples that are relevant to ultracold-atom experiments. This general method, which could be applied to various atomic species by means of fast-response protocols based on Fano-Feshbach resonances, opens the route for exploration of strongly correlated matter in synthetic dimensions.

We experimentally investigate the collective decay of a single Rydberg superatom, formed by an ensemble of thousands of individual atoms supporting only a single excitation due to the Rydberg blockade. Instead of observing a constant decay rate determined by the collective coupling strength to the driving field, we show that the enhanced emission of the single stored photon into the forward direction of the coupled optical mode depends on the dynamics of the superatom before the decay. We find that the observed decay rates are reproduced by an expanded model of the superatom which includes coherent coupling between the collective bright state and subradiant states.

Optomechanical systems are promising platforms for controlled light-matter interactions. They are capable of providing several fundamental and practical novel features when the mechanical oscillator is cooled down to nearly reach its ground state. In this framework, measuring the effective temperature of the oscillator is perhaps the most relevant step in the characterization of those systems. In conventional schemes, the cavity is driven strongly, and the overall system is well-described by a linear (Gaussian preserving) Hamiltonian. Here, we depart from this regime by considering an undriven optomechanical system via non-Gaussian radiation-pressure interaction. To measure the temperature of the mechanical oscillator, initially in a thermal state, we use light as a probe to coherently interact with it and create an entangled state. We show that the optical probe gets a nonlinear phase, resulting from the non-Gaussian interaction, and undergoes an incoherent phase diffusion process. To efficiently infer the temperature from the entangled light-matter state, we propose using a nonlinear Kerr medium before a homodyne detector. Remarkably, placing the Kerr medium enhances the precision to nearly saturate the ultimate quantum bound given by the quantum Fisher information. Furthermore, it also simplifies the thermometry procedure as it makes the choice of the homodyne local phase independent of the temperature.

Topological phases and edge-state topological protection are explicitly related by the bulk-edge correspondence which assumes the existence a real space boundary in one-dimensional (1D), 2D, or 3D systems. Extensions of this picture to systems where the boundary is present in the domain of generalized coordinates may generate unusual topological behavior in real space. In this paper, we discuss topological radial states in molecules with rotational symmetry and staggered hopping amplitudes in the radial direction. In the absence of the central site, the model is characterized as a weak topological insulator supporting radial edge states in the topological phase. When the central site is considered, we show that it behaves as an effective perturbation coupled in different ways to the radial inner edge, depending on the type of orbital considered at this central site. Tuning the parameters of the central orbital allows for a precise control over the radial inner edge physics of the model. We further break rotational symmetry by studying sliced molecules, which creates open boundaries in the azimuthal direction also, and show that higher-order boundary (corner) modes are present and how they can be driven into an energy gap through coupling with the central orbital. The results are corroborated by numerical conductance studies.

We derive generalized Kronig identities expressing quadratic fermionic terms including momentum transfer to bosonic operators and use them to obtain the exact solution for one-dimensional fermionic models with linear dispersion in the presence of position-dependent local interactions and scattering potential. In these Luttinger droplets, which correspond to Luttinger liquids with spatial variations or constraints, the position dependencies of the couplings break the translational invariance of correlation functions and modify the Luttinger-liquid interrelations between excitation velocities.

In recent years there has been a growing interest in the physical implementation of classical spin models through networks of optical oscillators. However, a key missing step in this mapping is to formally prove that the dynamics of such a nonlinear dynamical system is toward minimizing a global cost function which is equivalent with the spin model Hamiltonian. Here we introduce a minimal dynamical model for a network of dissipatively coupled optical oscillators and prove that the dynamics of such a system is governed by a Lyapunov function that serves as a cost function for the system. This cost function is in general a function of both phases and intensities of the oscillators and depends strongly on the pump parameter. In the case of bipartite network topologies, the amplitudes of the oscillators become identical in the steady state and the cost function reduces to the $XY$ Hamiltonian. In the general case for nontrivial network topologies, however, the cost function approaches the $XY$ Hamiltonian only in the strong pump limit. We show that by adiabatically tuning the pump parameter, the network can largely avoid trapping into the local minima of the governing cost function and stabilize into the ground state of the associated $XY$ Hamiltonian. These results show the great potential of laser networks for unconventional computing.

We analyze the disorder-driven localization of the two-dimensional Bose-Hubbard model by evaluating the full low-energy quasiparticle spectrum via a recently developed fluctuation operator expansion method. For any strength of the local interaction we find a mobility edge that displays an approximately exponential decay with increasing disorder strength. We determine the finite-size scaling collapse and exponents at this critical line finding that the localization of excitations is characterized by weak multifractality and a thermal-like critical gap ratio. A direct comparison to a recent experiment yields an excellent match of the predicted finite-size transition point and scaling of single particle correlations.

We develop a minimal model to describe growing dense active matter such as biological tissues, bacterial colonies, and biofilms, which are driven by a competition between particle division and steric repulsion. We provide a detailed numerical analysis of collective and single-particle dynamics. We show that the microscopic dynamics can be understood as the superposition of an affine radial component due to the global growth, and of a more complex nonaffine component that displays features typical of driven soft glassy materials, such as aging, compressed exponential decay of time correlation functions, and a crossover from superdiffusive behavior at short scales to subdiffusive behavior at larger scales. This analogy emerges because particle division at the microscale leads to a global expansion, which then plays a role analogous to shear flow in soft driven glasses. We conclude that growing dense active matter and sheared dense suspensions can generically be described by the same underlying physics.

Cross-correlation between magnetism and dielectric is expected to offer distinct emergent phenomena. Here, magnetic excitations in the organic donor-acceptor spin-chain system, tetrathiafulvalene-bromanil (TTF-BA), with a ferroelectric ground state is investigated by ${}^1\mathrm{H}$-NMR spectroscopy. A nonmagnetic transition with a ferroelectric order is marked by sharp drops in the NMR shift and the nuclear spin relaxation rate $T_1^{-1}$ at 53 K. Remarkably, the analyses of the NMR shift and $T_1^{-1}$ dictate that the paramagnetic spin susceptibility in TTF-BA is substantially suppressed from that expected for the one-dimensional Heisenberg spins. We propose that the spin-lattice coupling and the ferroelectric instability cooperate to promote precursory polar singlet formation in the ionic spin system with a nonmagnetic ferroelectric instability.

We propose to characterize Lévy-distributed stochastic fluctuations through the measurement of the average voltage drop across a current-biased Josephson junction. We show that the noise induced switching process in the Josephson washboard potential can be exploited to reveal and characterize Lévy fluctuations, also if embedded in a thermal noisy background. The measurement of the average voltage drop as a function of the noise intensity allows to infer the value of the stability index that characterizes Lévy-distributed fluctuations. An analytical estimate of the average velocity in the case of a Lévy-driven escape process from a metastable state well agrees with the numerical calculation of the average voltage drop across the junction. The best performances are reached at small bias currents and low temperatures, i.e., when both thermally activated and quantum tunneling switching processes can be neglected. The effects discussed in this work pave the way toward an effective and reliable method to characterize Lévy components eventually present in an unknown noisy signal.

As biochemical systems may frequently suffer from limited energy resources, so that internal molecular fluctuation has to be utilized to induce random rhythm, it is still a great theoretical challenge to understand the elementary principles for biochemical systems with limited energy resources to maintain phase accuracy and phase sensitivity. Here, we address the issue by deriving the energy-accuracy and the sensitivity-accuracy trade-off relations for a general biochemical model, analytically and numerically. We find that biochemical systems have a much lower energy cost by using noise-induced oscillations to keep almost equal efficiency to maintain precise processes compared with the energy cost using normal oscillations, clearly elucidating a survival mechanism when energy resources are limited. Moreover, an optimal system size is predicted where both the highest sensitivity and highest accuracy can be reached at the same time, providing a new strategy for the design of biological networks with limited energy sources.

Wearable thermoelectric conversion devices are one of the key technologies for future sustainable society, and flexible conducting polymer films are strong candidates for these applications. However, the thermoelectric transport mechanism of these materials is still unclear due to their unique disordered nature, in particular the poor interconnectivity between crystalline domains. Here, to overcome this limit, donor-acceptor (D-A) copolymer films are selected because of the efficient connection between domains via rigid tie molecules. We investigated their thermoelectric and carrier transport properties using the electrolyte-gating technique and perfectly described both of them based on the two-dimensional variable range hopping model with a linear density of states around the Fermi level energy. The present results provide a fundamental understanding of the thermoelectric physics in D-A copolymer films towards application in wearable devices.

Quantum entanglement is a quantum-mechanical phenomenon where the quantum state of a many-body system with many degrees of freedom cannot be described independently of the state of each body with a given degree of freedom, no matter how far apart in space each body is. Entanglement is not only considered a resource in quantum information but is also believed to affect complex condensed-matter systems. Detecting and quantifying multiparticle entanglement in a many-body system is thus of fundamental significance for both quantum information science and condensed-matter physics. Here, we detect and quantify multipartite entanglement in a spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain in a bulk solid. Multipartite entanglement was detected by using quantum Fisher information which was obtained using dynamic susceptibility measured via inelastic neutron scattering. The scaling behavior of quantum Fisher information was found to identify the spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain to belong to a class of strongly entangled quantum phase transitions with divergent multipartite entanglement.

Scalable quantum systems require deterministic entangled photon pair sources. Here, we demonstrate a scheme that uses a dipole-coupled emitter pair to deterministically emit polarization-entangled photon pairs. Based on this scheme, we predict spectroscopic signatures and quantify the entanglement with realistic material parameters. In addition, we describe how the Bell state fidelity and efficiency can be optimized by precisely tuning transition frequencies. Finally, we discuss how defect emitters are natural candidates for the proposed scheme, offering numerous advantages including flexible on-chip photonic integration and tunable emission properties via external fields, electromagnetic environments, and defect selection.