Equilibrium probes have been widely used in various schemes of sensing to quantum reservoirs. Many previous studies assumed that the probe-reservoir coupling is sufficiently weak such that the equilibrium state of the probe is approximately described by a canonical Gibbs state at the same temperature of the reservoir. Such a weak-coupling approximation severely restricts the range of application for an equilibrium-probe-based quantum sensing scenario. Going beyond the weak-coupling limitation, we here investigate the noncanonical effect, which is naturally induced by strong couplings, on the performance of a quantum sensing scheme. In this scheme, a quantum two-level system is used as the probe to estimate the parameters of a dissipative bosonic reservoir, by employing the polaron transformation approach. It is found that, compared with that of the canonical-equilibrium-state case, the noncanonical effect can effectively boost the sensing precision at both zero and finite temperatures. Paving the way toward realizing high-precision quantum sensing in practice, our result reveals the positive role of noncanonicality in the studies of quantum technologies.

The collective dynamics of active particles with topological vision are investigated. The topological vision, defined as a combination of the visual field and topological neighborhoods, breaks the action-reaction symmetry, thereby indicating that active particles exhibit the nonreciprocal topological interactions. Furthermore, our model considers position-based attractive force, wherein moving particles navigate using instantaneous visual information from neighboring particles within the topological vision, distinct from conventional models based on the velocity-velocity alignment. We demonstrate that the competition between the noise and the nonreciprocal topological interactions results in the emergence of four typical phases: gas phase, ordered phase, nematic bands, and aggregate traveling polar band. Moreover, the nonreciprocal topological interactions impact both anomalous diffusion and ergodicity breaking. Specifically, the weak nonreciprocal topological interactions lead to ergodic subdiffusion, while the strong nonreciprocal topological interactions give rise to nonergodic superdiffusion. These findings provide a theoretical basis for understanding the nonequilibrium collective transport of active particles with topological vision.

The anomalous bulk-boundary correspondence in non-Hermitian systems featuring an intricate interplay between skin and boundary modes has attracted enormous theoretical and experimental attention. Still, in dimensions higher than one, this interplay remains much less understood. Here we provide insights from exact analytical solutions of a large class of models in any dimension $d$, with open boundaries in $d_c\le d$ directions, and by tracking their topological origin. Specifically, we show that amoeba theory accounting for the separation gaps of the bulk modes augmented with higher-dimensional generalizations of the biorthogonal polarization and the generalized Brillouin zone approaches accounting for the surface gaps of boundary modes provide a comprehensive understanding of these systems.

The gravity model is a mathematical model that applies Newton's universal law of gravitation to socioeconomic transport phenomena and has been widely used to describe world trade, intercity traffic flows, and business transactions for several decades. However, its strong nonlinearity and diverse network topology make a theoretical analysis difficult, and only a short history of studies on its stability exists. In this study, the stability of gravity models defined on networks with few nodes is analyzed in detail using numerical simulations. It was found that, other than the previously known transition of stationary solutions from a unique diffusion solution to multiple localized solutions, parameter regions exist where periodic solutions with the same repeated motions and chaotic solutions with no periods are realized. The smallest network with chaotic solutions was found to be a ring with seven nodes, which produced a new type of chaotic solution in the form of a mixture of right and left periodic solutions.

In recent years, distributed quantum sensing has gained interest for a range of applications requiring networks of sensors, from global-scale clock synchronization to high energy physics. In particular, a network of entangled sensors can improve not only the sensitivity beyond the shot noise limit, but also enable a Heisenberg scaling with the number of sensors. Here, using bright entangled twin beams, we theoretically and experimentally demonstrate the detection of a linear combination of two distributed phases beyond the shot noise limit with a truncated SU(1,1) interferometer. Specifically, we show a quantum noise reduction of $1.7\pm 0.3$ dB below what is possible with the corresponding classical configuration. Additionally, we theoretically extend the use of a truncated SU(1,1) interferometer to a multi-phase-distributed sensing scheme that leverages entanglement as a resource to achieve a quantum improvement in the scaling with the number of sensors in the network. Our results pave the way for developing quantum-enhanced sensor networks that can achieve an entanglement-enhanced sensitivity.

Dynamical systems can display a plethora of ergodic and ergodicity breaking behaviors, ranging from simple periodicity to ergodicity and chaos. Here we report an unusual type of nonergodic behavior in a many-body discrete-time dynamical system, specifically a multiperiodic response with multifractal distribution of equilibrium spectral weights at all rational frequencies. This phenomenon is observed in the momentum-conserving variant of the newly introduced class of the so-called parity check reversible cellular automata, which we define with respect to an arbitrary bipartite lattice. Although the models display strong fragmentation of phase space of configurations, we demonstrate that the effect qualitatively persists within individual fragmented sectors, and even individual typical many-body trajectories. We provide detailed numerical analysis of examples on 2D (honeycomb, square) and 3D (cubic) lattices.

Creating a coherent source of gamma radiation remains one of the biggest motivations in gamma-ray optics. Such a source would utilize the stimulated emission of gamma photons. However, to achieve lasing in the high-energy regime other physical principles such as the lasing without inversion are needed to be explored. One of the currently developed approaches uses coherent control of gamma radiation waveforms to induce transparency in a medium by applying ultra-acoustic vibrations. In this paper a theoretical description of the stimulated emission and coherent control of gamma rays is developed on the basis of a one-dimensional quantum mechanical formalism. The model of the gamma radiation coherent control shows a good agreement with the conventional semiclassical description of the phenomenon. The model of the stimulated emission was developed with the assumptions which enable to propose a specific experimental arrangement for simultaneous detections of pairs of gamma photons. This proposal is further discussed in the context of the experimental observation of the stimulated emission of gamma photons.

We consider the quantum magic in systems of dense neutrinos undergoing coherent flavor transformations, relevant for supernova and neutron-star binary mergers. Mapping the three-flavor-neutrino system to qutrits, the evolution of quantum magic is explored in the single scattering angle limit for a selection of initial tensor-product pure states for $N_{\nu }\le 8$ neutrinos. For $|{\nu }_e{\rangle }^{\otimes N_{\nu }}$ initial states, the magic, as measured by the $\alpha =2$ stabilizer Renyi entropy ${\mathcal{M}}_2$, is found to decrease with radial distance from the neutrino sphere, reaching a value that lies below the maximum for tensor-product qutrit states. Further, the asymptotic magic per neutrino, ${\mathcal{M}}_2/N_{\nu }$, decreases with increasing $N_{\nu }$. In contrast, the magic evolving from states containing all three flavors reaches values only possible with entanglement, with the asymptotic ${\mathcal{M}}_2/N_{\nu }$ increasing with $N_{\nu }$. These results highlight the connection between the complexity in simulating quantum physical systems and the parameters of the Standard Model.

In the era of noisy intermediate-scale quantum computers, variational quantum algorithms are promising approaches for solving optimization tasks by training parameterized quantum circuits with the aid of classical routines informed by quantum measurements. In this context, photonic platforms based on reconfigurable integrated optics are an ideal candidate for implementing these algorithms. Among various techniques to train variational circuits, the parameter shift rule enables the exact calculation of cost function derivatives efficiently, facilitating gradient descent-based optimization. In this paper, we derive a formulation of the parameter shift rule for computing derivatives and integrals tailored to reconfigurable optical linear circuits and based on the Boson Sampling paradigm. This allows us to naturally embed common types of experimental noise, such as partial distinguishability and mixedness of the states, thus obtaining a resilient approach. Finally, we employ the developed approach to experimentally test variational algorithms with single-photon states processed in a reconfigurable six-mode universal integrated interferometer. Specifically, we apply the photonic parameter shift rules to the variational implementation, on a photonic platform, of both an eigensolver and a Universal-not gate.

The rheological response and chain dynamics of thin polymer films underpin nanoscale polymer processing, yet molecular confinement alters such behavior. Using the interfacial wetting force of an immiscible liquid droplet to deform the films and linear elastic theory to describe the time evolution of the deformation profile, we demonstrated that the linear viscoelastic spectra, i.e., the frequency-dependent storage and loss moduli, of nanoscale polymer films are experimentally accessible over a wide frequency range. Our measurements on polystyrene nanofilms evidence an acceleration of polymer diffusion at a large confining length scale, i.e., at film thicknesses of hundreds of nanometers. This long-range perturbation in chain dynamics was interpreted as the fast relaxation of surface chains with reduced entanglements provoking loosening of entanglement constraints of the underlying chains, allowing the accelerated reptation mobility at the surface to extend deeply into the film interior. This suggests a surface-induced constraint release effect dominating the dynamics and rheology of polymers confined at a large length scale.

We use stochastic closure theory and generalized Green-Kubo relations to show that the velocity structure functions have two distinct scaling regimes connected by a passover. Initially, after a brief ballistic (Batchelor) scaling, the structure functions exhibit a Lagrangian scaling regime with no intermittency, and then pass over to a regime with Eulerian scaling, with intermittency. This transition time for the passover region is controlled by the second structure function, through a generalization of Green-Kubo-Obukhov relations. The ultimate time interval of decay seems to be controlled by the scaling of free eddies, analogous to the scaling in the buffer layer of boundary layer turbulence [B. Birnir, L. Angheluta, J. Kaminsky, and X. Chen, Spectral link of the Generalized Townsend-Perry constants in turbulent boundary layers, Phys. Rev. Res. 3, 043054 (2021)]. The dip observed in the log-derivatives of the structure function [L. Biferale, E. Bodenschatz, M. Cencini, A. S. Lanotte, N. T. Ouellette, F. Toschi, and H. Xu, Lagrangian structure functions in turbulence: A quantitative comparison between experiment and direct numerical simulation, Phys. Fluids 20, 065103 (2008)], with respect to the second structure function $S_2$, is caused only by the time scales probed by $S_2$. It seems better to take the log-derivative with respect to $t$, instead of $S_2$, to fully understand the different scaling regimes of Lagrangian turbulence.

In a multiqubit system, when a detector's resolution is insufficient to distinguish between qubits, individual qubit measurement becomes impractical. This limitation results in coarse-grained (CG) measurements that dilute system information and, more critically, hinder accurate assessment of qubit correlations, making quantum state tomography (QST) infeasible. To address this issue, we propose a scheme to utilize CG measurements for QST by integrating two-qubit gates and optimizing their corresponding positive operator-valued measures (POVMs) using parametrized quantum circuits. Specifically, we focus on constructing generalized symmetric informationally complete POVMs by maximizing the von Neumann entropy of the Gram matrix of these CG POVMs. Our numerical simulations demonstrate the effectiveness of this approach for QST using a two-qubit model and further verify the scalability of our scheme toward $N$-qubit systems.

We develop a hydrodynamic description of self-generated electrolyte flow in capillaries whose bounding walls feature both nonuniform distributions of charge and nonuniform active ionic fluxes. The hydrodynamic velocity arising in such a system has components that are forbidden by symmetry in the absence of charge and fluxes. However, when these two boundary mechanisms are simultaneously present, they can lead to a symmetry broken state where steady flows with both unidirectional and circulatory components emerge. We show that these flow states arise when modulated boundary patterns of charge and fluxes are offset by a flux-charge phase difference, which is associated with the separation between sites of their peak densities on the wall. Mismatch in diffusivity of cationic and anionic species can modify the flow states and becomes an enhancing factor when fluxes of both ion species are being produced together at the same site. We demonstrate that this mechanism can be realized with a microfluidic generator that is powered by enzyme-coated patches that catalyze reactants in the solution to produce fluxes of ions. The local ionic elevation or depletion, which disrupts a nonuniform double layer, promotes self-induced gradients yielding persistent body forces to generate bulk fluid motion. Our work quantifies a boundary-driven mechanism behind self-sustained electrolyte flow in confined environments that exists without any external bulk-imposed fields or gradients. It provides a theoretical framework for understanding the combined effect of active and charged boundaries that are relevant in biological or soft matter systems, and can be utilized in electrofluidic and iontronic applications.

Extracting meaningful information about unknown quantum states without performing a full tomography is an important task. Low-dimensional projections and random measurements can provide such insight but typically require careful crafting. In this paper, we present an optical scheme based on sending unknown input states through a multimode fiber and performing two-point intensity and coincidence measurements. A short multimode fiber implements effectively a random projection in the spatial domain, while a long-dispersive multimode fiber performs a spatial and spectral projection. We experimentally show that useful properties, i.e., the purity, dimensionality, and degree of indistinguishability of various states of light including spectrally entangled biphoton states, can be obtained by measuring statistical properties of single counts and their correlation between two outputs over many realizations of unknown random projections. Moreover, we show that this information can then be used for state classification.