We use scanning gate microscopy to demonstrate the presence of localized states arising from potential inhomogeneities in a $50\mathrm{nm}$ wide, gate-defined conducting channel in encapsulated bilayer graphene. When imaging the channel conductance under the influence of a local tip-induced potential, we observe ellipses of enhanced conductance as a function of the tip position. These ellipses allow us to infer the location of the localized states and to study their dependence on the displacement field. For large displacement fields, we observe that localized states tend to occur halfway into the channel. All our observations can be well explained within the framework of stochastic Coulomb blockade.

We formulate a generalized susceptible exposed infectious recovered (SEIR) model on a graph, describing the population dynamics of an open crowded place with an arbitrary topology. As a sample calculation, we discuss three simple cases, both analytically and numerically, by means of a cellular automata simulation of the individual dynamics in the system. As a result, we provide the infection ratio in the system as a function of controllable parameters, which allows for quantifying how acting on the human behavior may effectively lower the disease spread throughout the system.

A general description to estimate optical trapping efficiencies for dielectric nanoparticles using dipole approximation is presented including the effect of optical nonlinearity. We show how optical nonlinearity can be harnessed to trap particles having a refractive index less than that of the surrounding medium. We also discuss optical trapping efficiencies of particles made of metamaterials of negative refractive indices. These results are promising in having wide-ranging applications in photonics science and technology.

We report the observation of a two-dimensional (2D) checkerboard charge density wave (CDW) in the low-dimensional superconductor ${\mathrm{Ta}}_4{\mathrm{Pd}}_3{\mathrm{Te}}_{16}$. By determining its CDW properties across the temperature-pressure ($T-P$) phase diagram and comparing with prototypical CDW materials, we conclude that ${\mathrm{Ta}}_4{\mathrm{Pd}}_3{\mathrm{Te}}_{16}$ features (a) an incommensurate CDW with a mixed character of dimensions [quasi-1D (Q1D) considering its needlelike shape along the $\mathrm{b}$ axis, Q2D as the CDW has checkerboard wave vectors, and 3D because of CDW projections along all three axes], and (b) one of the weakest CDWs compared to its superconductivity (SC), i.e., enhanced SC with respect to CDW, suggesting an interesting interplay of the two orders.

Recent theoretical investigations have indicated that rapid optical cycling should be feasible in complex polyatomic molecules with diverse constituents, geometries, and symmetries. However, as a composite molecular mass grows, so does the required number of photon scattering events necessary to decelerate and confine molecular beams using laser light. Utilizing coherent momentum exchange between light fields and molecules can suppress spontaneous emission and significantly reduce experimental complexity for slowing and trapping. Working with BaH as a test species, we have identified a robust, experimentally viable configuration to achieve large molasses-like cooling forces for molecules using polychromatic optical fields addressing both $X\text{−}A$ and $X\text{−}B$ electronic transitions, simultaneously. Using numerical solutions of the time-dependent density matrix as well as Monte Carlo simulations, we demonstrate that creation of suppressed emission rate (SupER) molasses with large capture velocities $(\sim 40 \mathrm{m}/\mathrm{s})$ is generically feasible for polyatomic molecules of increasing complexity that have an optical cycling center. Proposed SupER molasses are anticipated to not only extend quantum control to novel molecular species with abundant vibrational decay channels, but also significantly increase trapped densities for previously laser-cooled diatomic and triatomic species.

Quantum measurements and the associated state changes are properly described in the language of instruments. We investigate the properties of a time continuous family of instruments associated with the recently introduced class of general Gaussian non-Markovian stochastic Schrödinger equations. In this article we find that when the covariance matrix for the Gaussian noise satisfies a particular $\delta$-function constraint, the measurement interpretation is possible for a class of models with self-adjoint coupling operator. This class contains, for example the spin-boson and quantum Brownian motion models with colored bath correlation functions. Remarkably, due to quantum memory effects the reduced state, in general, does not obey a closed form master equation while the unraveling has a time continuous measurement interpretation.

From the spread of pollutants in the atmosphere to the transmission of nutrients across cell membranes, anomalous diffusion processes are ubiquitous in natural systems. The ability to understand and control the mechanisms guiding such processes across various scales has important application to research in materials science, finance, medicine, and energetics. Here we present a numerical study of anomalous diffusion of light through a semicrystalline polymer structure where transport is guided by random disorder and nonlocal interactions. The numerical technique examines diffusion properties in one-dimensional (1D) space via the spectrum of an Anderson-type Hamiltonian with a discrete fractional Laplacian operator ${\left(-\mathrm{\Delta }\right)}^s$, $s\in \left(0,2\right)$ and a random distribution of disorder. The results show enhanced transport for $s<1$ (superdiffusion) and enhanced localization for $s>1$ (subdiffusion) for most examined cases. An important finding of the present study is that transport can be enhanced at key spatial scales in the subdiffusive case, where all states are normally expected to be localized for a (1D) disordered system.

In isolated quantum systems that have conserved quantities, such as energy and total magnetization, the conserved quantities cannot vary their values with their own dynamics. To violate conservation laws of the system keeping the unitary nature in the system's dynamics, quantum coherence must be supplied from the outer environment. This provides a general and abstract interpretation of the underlying mechanism of unitary operations on systems of interest. In this paper, we consider the amount of quantum coherence cost to realize the desired unitary operation. We derive upper and lower bounds for the coherence cost to implement arbitrary unitary operation within the desired error. These two bounds asymptotically match each other in a small error regime, and give an asymptotic equality. We present applications of our theories to several physical situations such as quantum heat engines and entanglement erasure.

We present a model of static and dynamic properties of uniaxial nematic liquid crystals that brings together the advantages of the Oseen-Frank (OF), Landau–de Gennes (LdG), and Ericksen-Leslie (EL) models. The model is based on the introduced vector $\mathbf{N}=\sqrt{s}\widehat{\mathbf{n}}$, called nemator, which defines both the director $\widehat{\mathbf{n}}$ and the uniaxial order parameter $s$. The equilibrium nemator field is determined from minimization of the free energy, which contains the microscopic and macroscopic parts. The proposed microscopic term combines the features of the LdG and Maier-Saupe models, and its minimization provides a good fit of temperature dependence of $s$ in the entire nematic phase. We derive the macroscopic part as a complete set of elastic, magnetic, dielectric and flexoelectric terms. The dynamic equations for the nemator, flow velocity, and pressure are derived using the conservation laws of mass, linear and angular momenta, and energy. The nemator model contains no nemator gradients and thus does not create a singularity when $\mathbf{N}$ flips, allowing simulations of static and dynamic patterns with semi-integer disclinations and other defects. Comparison of the nemator model with the OF, LdG, and EL models reveals that the material parameters and viscous coefficients in the nemator model are nonzero when N → 0 and can be determined from the existing experimental data.

We develop a method that uses truncation-order-dependent reexpansions constrained by generic strong-coupling information to extrapolate perturbation series to the nonperturbative regime. The method is first benchmarked against a zero-dimensional model field theory and then applied to the dilute Fermi gas in one and three dimensions. Overall, our method significantly outperforms Padé and Borel extrapolations in these examples. The results for the ground-state energy of the three-dimensional Fermi gas are robust with respect to changes in the form of the reexpansion and compare well with quantum Monte Carlo simulations throughout the BCS regime and beyond.

Chalcogenide semiconductors and semimetals are a fertile class of efficient thermoelectric materials, which, in most cases, exhibit very low lattice thermal conductivity ${\kappa }_{\mathrm{ph}}$ despite lacking a complex crystal structure such as the tetragonal binary compound InTe. Our measurements of ${\kappa }_{\mathrm{ph}}\left(T\right)$ in single-crystalline InTe along the $c$ axis show that ${\kappa }_{\mathrm{ph}}$ exhibits a smooth temperature dependence upon cooling to about 50 K, the temperature below which a strong rise typical for dielectric compounds is observed. Using a combination of first-principles calculations, inelastic neutron scattering (INS), and low-temperature specific heat and transport properties measurements on single-crystalline InTe, we show that the phonon spectrum exhibits well-defined acoustic modes, the energy dispersions of which are constrained to low energies due to distributions of dispersionless, optical modes, which are responsible for a broad double peak structure in the low-temperature specific heat. The latter are assigned to the dynamics of ${\mathrm{In}}^{+}$ cations in tunnels formed by edge-sharing ${\left({\mathrm{In}}^{3+}{{\mathrm{Te}}_4}^{2-}\right)}^{-}$ tetrahedra chains, the atomic thermal displacement parameters of which, probed as a function of temperature by means of single-crystal x-ray diffraction, suggest the existence of a complex energy potential. Indeed, the ${\mathrm{In}}^{+}$-weighted optical modes are not observed by INS, which is ascribed to the anharmonic broadening of their energy profiles. While the low ${\kappa }_{\mathrm{ph}}$ value of $1.2\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 300 K originates from the limited energy range available for acoustic phonons, we show that the underlying mechanism is specific to InTe and argue that it is likely related to the presence of local disorder induced by the ${\mathrm{In}}^{+}$ site occupancy.

Theoretical approaches to binary-state models on complex networks are generally restricted to infinite size systems, where a set of nonlinear deterministic equations is assumed to characterize its dynamical and stationary properties. We develop in this work the stochastic formalism of the different compartmental approaches, these are the approximate master equation (AME), pair approximation (PA), and heterogeneous mean-field (HMF), in descending order of accuracy. The stochastic formalism allows us to enlarge the range of validity and applicability of compartmental approaches. This includes (i) the possibility of studying the role of the size of the system in the different phenomena reproduced by the models together with a network structure, (ii) obtaining the finite-size scaling functions and critical exponents of the macroscopic quantities, and (iii) the extension of the rate description to a more general class of models.

Molecular transport in dense, crowded media is often affected by binding and collisions with obstacles, leading to complex spatial distributions and anomalous diffusion on multiple length scales. Here, neutron spin-echo (NSE) spectroscopy and forced Rayleigh scattering (FRS) were used in tandem to study the interplay between segmental and center-of-mass chain dynamics in the presence of strong binding interactions in a model protein hydrogel. The results provide evidence for several dynamic scaling regimes of gel relaxation behavior with varying length scale, including a caging regime bridging submolecular relaxation and center-of-mass diffusion due to transient binding. On mesoscopic length scales larger than the size of the cage, chains undergo two distinct regimes of apparent superdiffusive scaling, with different power-law exponents, before the onset of terminal Fickian diffusion. The combined NSE and FRS results are interpreted in the context of prior Brownian dynamics simulations of associating star polymers, revealing insight into structural length scales and binding kinetics governing the transition from segmental relaxation to self-diffusion in the protein hydrogel. Finally, single-sticker tracer diffusion measurements were performed to directly probe sticker association/dissociation dynamics within the gel, the results suggesting that cooperative cluster motion may play a role in network relaxation on larger length scales.

A number of experimental platforms for quantum simulations of disordered quantum matter, from dipolar systems to trapped ions, involve degrees of freedom which are coupled by power-law decaying hoppings or interactions, yet the interplay of disorder and interactions in these systems is far less understood than in their short-ranged counterpart. Here, we consider a prototype model of interacting fermions with disordered long-ranged hoppings and interactions and use the flow equation approach to map out its dynamical phase diagram as a function of hopping and interaction exponents. We demonstrate that the flow equation technique is ideally suited to problems involving long-range couplings due to its ability to accurately simulate very large system sizes. We show that at large on-site disorder and for short-range interactions, a transition from a delocalized phase to a quasi-many-body localized (MBL) phase exists as the hopping range is decreased. This quasi-MBL phase is characterized by intriguing properties such as a set of emergent conserved quantities which decay algebraically with distance. Surprisingly, we find that a crossover between delocalized and quasi-MBL phases survives even in the presence of long-range interactions.

The production, exchange, and balance of entropy characterize the thermodynamics of open nonequilibrium systems, ranging from chemical reactions, cells, ecological systems, and Earth-like planets to stars. We generalize the Glansdorff-Prigogine general evolution criterion to constrain the entropy balance in volumetric open-flow chemical reaction systems. We derive a thermodynamic inequality governing the joint evolution of both the internal microreversible reactions and the matter fluxes that the system exchanges with its environment, as exemplified by the distribution of the entropy productions and exchanges over the chemical reaction pathways. We validate this evolution theorem and discuss the physical significance of this pathwise partitioning of the dissipation, for an autocatalytic model capable of spontaneous mirror symmetry breaking.

Here, we present a detailed theoretical and experimental study on the pressure induced switching of the anomalous Hall effect (AHE) in the triangular antiferromagnetic (AFM) compound ${\mathrm{Mn}}_3\mathrm{Sn}$. Our theoretical model suggests pressure driven significant splitting of the in-plane Mn bond lengths, i.e., an effective trimerization, which in turn stabilizes a helical AFM ground state by modifying the interplane exchange parameters in the system. We experimentally demonstrate that the AHE in ${\mathrm{Mn}}_3\mathrm{Sn}$ reduces from $5\mu \mathrm{\Omega }$ cm at ambient pressure to zero at an applied pressure of about 1.5 GPa. Furthermore, our pressure dependent magnetization study reveals that the conventional triangular AFM ground state of ${\mathrm{Mn}}_3\mathrm{Sn}$ systematically transforms into the helical AFM phase where the symmetry does not support a nonvanishing Berry curvature required for the realization of a finite AHE. The pressure dependent x-ray diffraction study rules out any role of structural phase transition in the observed phenomenon. In addition, the temperature dependent in-plane lattice parameter at ambient pressure is found to deviate from the monotonic behavior when the system enters into the helical AFM phase, thereby supporting the proposed impact of trimerization in controlling the AHE. We believe that the present study makes an important contribution toward understanding the stabilization mechanism of different magnetic ground states in ${\mathrm{Mn}}_3\mathrm{Sn}$ and related materials for their potential applications pertaining to AHE switching.

If one-electron observables of a many-electron system are of interest, a many-electron dynamics can be represented exactly by a one-electron dynamics with effective potentials. The formalism for this reduction is provided by the exact electron factorization (EEF). We study the time-dependent features of the EEF effective potentials for a model of an atom ionized by an ultrastrong and ultrashort laser pulse, with the aim of understanding what is needed to develop computationally feasible approximations. It is found that the simplest approximation, the so-called time-independent conditional amplitude (TICA) approximation, is complementary to single-active electron approaches as it reproduces the exact dynamics well for high-photon frequencies of the laser field or large Keldysh parameter. For relatively low frequencies of the laser field or for smaller Keldysh parameters, we find that excited-state dynamics in the core region of the atom leads to a time-dependent ionization barrier in the EEF potential. The time dependence of the barrier needs to be described accurately to correctly model many-electron effects, and we conclude that a multistate extension of the TICA approximation is a possible route as to how this can be achieved. In general, our study sheds a different light on one-electron pictures of strong-field ionization and shows that many-electron effects for such processes may be included by solving a one-electron Schrödinger equation, provided the core dynamics can be modeled successfully.

Parametrized quantum evolution is the main ingredient in variational quantum algorithms for near-term quantum devices. In digital quantum computing, it has been shown that random parametrized quantum circuits are able to express complex distributions intractable by a classical computer, leading to the demonstration of quantum supremacy. However, their chaotic nature makes parameter optimization challenging in variational approaches. Evidence of similar classically intractable expressibility has been recently demonstrated in analog quantum computing with driven many-body systems. A thorough investigation of trainability of such analog systems is yet to be performed. In this work we investigate how the interplay between external driving and disorder in the system dictates the trainability and expressibility of interacting quantum systems. We show that if the system thermalizes, the training fails at the expense of the large expressibility, while the opposite happens when the system enters the many-body localized (MBL) phase. From this observation we devise a protocol using quenched MBL dynamics which allows accurate trainability while keeping the overall dynamics in the quantum supremacy regime. Our work shows the fundamental connection between quantum many-body physics and its application in machine learning. We conclude our work with an example application in generative modeling employing a well studied analog many-body model of a driven Ising spin chain. Our approach can be implemented with a variety of available quantum platforms including cold ions, atoms, and superconducting circuits.

After more than 80 years from the seminal work of Weizsäcker and the liquid drop model of the atomic nucleus, deviations from experiments of mass models $\left(\sim \mathrm{MeV}\right)$ are orders of magnitude larger than experimental errors $\left(\lesssim \mathrm{keV}\right)$. Predicting the mass of atomic nuclei with precision is extremely challenging. This is due to the nontrivial many-body interplay of protons and neutrons in nuclei, and the complex nature of the nuclear strong force. Statistical theory of learning will be used to provide the bounds to prediction errors of a model trained with a finite data set. These bounds are validated with neural network models and compared with state of the art mass models. It will be argued that nuclear structure mass models explore a system on the limit of the precision bounds, as defined by the statistical theory of learning.

Event occurrence is not only subject to the environmental changes, but is also facilitated by the events that have occurred in a system. Here, we develop a method for estimating such extrinsic and intrinsic factors from a single series of event-occurrence times. The analysis is performed using a model that combines the inhomogeneous Poisson process and the Hawkes process, which represent exogenous fluctuations and endogenous chain-reaction mechanisms, respectively. The model is fit to a given dataset by minimizing the free energy, for which statistical physics and a path-integral method are utilized. Because the process of event occurrence is stochastic, parameter estimation is inevitably accompanied by errors, and it can ultimately occur that exogenous and endogenous factors cannot be captured even with the best estimator. We obtained four regimes categorized according to whether respective factors are detected. By applying the analytical method to real time series of debate in a social-networking service, we have observed that the estimated exogenous and endogenous factors are close to the first comments and the follow-up comments, respectively. This method is general and applicable to a variety of data, and we have provided an application program, by which anyone can analyze any series of event times.