We study the interaction of emitters with a composite waveguide formed from two parallel optical nanofibers in regimes of experimental importance for atomic gases or solid-state emitters. Using the exact dyadic Green's function we comprehensively investigate the coupling efficiency and the fiber-induced Lamb shift accounting for variations in emitter positions and fiber configurations. This reveals coupling efficiencies and Purcell factors that are enhanced considerably beyond those using a single fiber waveguide, and robustness in the figures of merit. We finally investigate resonant dipole-dipole interactions and the generation of entanglement between two emitters mediated through the composite waveguide under excitation. We show that the concurrence can be enhanced for two fiber systems, such that entanglement may be present even in cases where it is zero for a single fiber. All-fiber systems are simple in construction and benefit from a wealth of existing telecommunications technologies, while enjoying strong couplings to emitters and offering interesting light-matter functionalities specific to slot waveguides.

Estimating properties of quantum states via randomized measurements has become a significant part of quantum information science. In this paper, we design an innovative approach leveraging metasurfaces to perform randomized measurements on photonic qubits, together with error mitigation techniques that suppress realistic metasurface measurement noise. Through fidelity and purity estimation, we confirm the capability of metasurfaces to implement randomized measurements and the unbiased nature of our error-mitigated estimator. Our findings show the potential of metasurface-based randomized measurement schemes in achieving robust and resource-efficient estimation of quantum state properties.

Multi-product formulas (MPFs) are linear combinations of Trotter circuits offering high-quality simulation of Hamiltonian time evolution with fewer Trotter steps. Here we report two contributions aimed at making multi-product formulas more viable for near-term quantum simulations. First, we extend the theory of Trotter error with commutator scaling developed by Childs et al. [A. M. Childs et al., Phys. Rev. X 11, 011020 (2021)] to multi-product formulas. Our result implies that multi-product formulas can achieve a quadratic reduction of Trotter error in 1-norm (nuclear norm) on arbitrary time intervals compared with the regular product formulas without increasing the required circuit depth or qubit connectivity. The number of circuit repetitions grows only by a constant factor. Second, we introduce dynamic multi-product formulas with time-dependent coefficients chosen to minimize a certain efficiently computable proxy for the Trotter error. We use a minimax estimation method to make dynamic multi-product formulas robust to uncertainty from algorithmic errors, sampling, and hardware noise. We call this method the minimax MPF and we provide a rigorous bound on its error.

Physical systems transition between states with finite speed that is limited by energetic costs. In this work, we derive bounds on transition times for general Langevin systems that admit a decomposition into reversible and irreversible dynamics, in terms of the Wasserstein distance between states and the energetic costs associated with respective reversible and irreversible currents. For illustration we discuss Brownian particles subject to arbitrary forcing and an RLC circuit with time-varying inductor.

In this study, we investigate the discrepancy between the estimate of Q. He et al. [Phys. Rev. Res. 3, L032074 (2021)], who observed a remarkable collapse of the exciton gap in ${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$ due to the electrostatic field between the scanning tunneling microscope (STM) tip and the sample, and that of a recent angle-resolved photoemission spectroscopy investigation [C. Chen et al., Phys. Rev. Res. 5, 043089 (2023)]. It is proposed that a critical factor contributing to this discrepancy is due to He et al.'s assumption of a constant work function of the STM tip. This assumption led to an underestimation of the tip-induced electric field. Using a literature value for the sample work function, a more substantial electric field strength is obtained, which resolves the apparent conflict between the doping estimates of these two techniques. Furthermore, our findings highlight the importance of the STM tip condition, which can significantly impact the tip work function and, consequently, influence the doping estimation in experiments involving tip-induced electric fields.

A common method for delineating urban and suburban boundaries is to identify clusters of spatial units that are highly interconnected in a network of mobility flows, each cluster signaling a cohesive economic submarket. It is critical that the methods employed for this task are principled and free of unnecessary tunable parameters to avoid unwanted inductive biases while remaining scalable for high-resolution mobility data. Here, we systematically assess the benefits and limitations of a wide array of stochastic block models (SBMs)—a family of principled, nonparametric models for identifying clusters in networks—for regionalization with mobility data. We find that the data compression capability and relative performance of different SBM variants heavily depend on the spatial extent of the mobility network, its aggregation scale, and the method used for weighting network edges. By constructing a measure to assess the degree to which a network partition violates spatial contiguity, we find that traditional SBMs may produce substantial spatial discontiguities that require extensive postprocessing to make them suitable for regionalization. We propose a fast nonparametric agglomerative algorithm to alleviate this issue, achieving data compression close to that of unconstrained SBM models while ensuring spatial contiguity, benefiting from a deterministic optimization procedure, and being generalizable to wide range of community detection objective functions.

Simulations of lattice gauge theories on noisy quantum hardware inherently suffer from violations of the gauge symmetry due to coherent and incoherent errors of the underlying physical system that implements the simulation. These gauge violations cause the simulations to become unphysical requiring the result of the simulation to be discarded. We investigate an active correction scheme that relies on detecting gauge violations locally and subsequently correcting them by dissipatively driving the system back into the physical gauge sector. We show that the correction scheme not only ensures the protection of the gauge symmetry, but it also leads to a longer validity of the simulation results even within the gauge-invariant sector. Finally, we discuss further applications of the scheme such as preparation of the many-body ground state of the simulated system.

The vision of deploying miniature vehicles within the human body for intricate tasks holds tremendous promise across engineering and medical domains. Herein, optimal navigation of a cargo-towing swimmer under an applied zig-zag flow is studied by employing direct numerical simulations coupled with a deep reinforcement learning algorithm. Tasks include navigation in flow and shear-gradient directions. We initially explore combinations of state inputs, finding that optimal navigation necessitates swimmers to perceive hydrodynamics and alignment, surpassing reliance solely on hydrodynamic signals while considering their memories. Next, we study combinations of action spaces, allowing dynamic changes in swimming and/or rotational velocities by tuning $B_1$ and $C_1$ parameters of the squirmer model, respectively. By keeping both parameters fixed, cargo-towing swimmers demonstrate superior performance in the flow direction compared to swimmers without load due to tumbling movements influenced by shear flow. In the shear-gradient direction, swimmers without load outperform cargo-towing swimmers, with performance decreasing as load length increases. Across the combination of allowing $B_1$ and $C_1$ to change, the policies from solely dynamic $B_1$ actions demonstrate superior navigation. The policies are then used as a showcase against naive cargo-towing and inert colloidal chains. A t-distributed stochastic neighbor embedding analysis reveals the complex interplay between perceived hydrodynamic signals and swimmer position. In the flow direction, swimmers align effectively with regions of maximum velocity, while in the shear-gradient direction, periodic transitions from minimum to maximum state values occur. Comparing pullers, pushers, and neutral swimmers, cargo-towing swimmers show a reversal in swimming velocity trends, with pullers outpacing neutral and pusher swimmers, irrespective of load lengths.

Microswimmers often use chirality to generate translational movement from rotation motion, exhibiting distinct behaviors in complex fluids compared to simple Newtonian fluids. However, the underlying mechanism remains incompletely understood. In this study, we elucidate the precise mechanisms underlying the distinct behaviors of microswimmers in Newtonian and non-Newtonian fluids. We show that the enhanced speed of chiral swimmers is attributed to the Weissenberg effect induced by normal stress differences resulting from chiral flows. Additionally, we identify swimmer-specific normal stress differences in a viscoelastic fluid and demonstrate that swimming speed varies depending on whether the swimmer acts as a pusher or a puller. Moreover, we investigate the hydrodynamic interactions between a pair of chiral squirmers. When the squirmers are aligned parallel (perpendicular) to their swimming axis, they tend to separate (approach). These findings deepen our comprehension of the rheological properties of viscoelastic fluids containing microswimmers, promising advancements in various applications.

In a paramagnetic state of a hyperkagome lattice antiferromagnet ${\mathrm{Mn}}_3\mathrm{RhSi}$, magnetic diffuse scattering by magnetic short-range order is observed over a wide temperature range of approximately 500 K above the Néel temperature of 190 K. We have studied the magnetic excitation with a single crystal in a wide energy range from 0.3 to 140 meV by inelastic neutron scattering, where the prominent inelastic neutron-scattering signal is observed at $\mathbf{Q}=(2,0,0)$. The inelastic scattering intensity integrated for two of twelve magnon modes leads to a localized magnetic moment of about 5 ${\mu }_{\mathrm{B}}$ per Mn site, although the long-range ordered magnetic moment is only 2.61 ${\mu }_{\mathrm{B}}$ at 4 K. The result suggests that a large part of the magnetic moment does not order in ${\mathrm{Mn}}_3\mathrm{RhSi}$, possibly due to the geometrical spin frustration of the hyperkagome lattice.

Harnessing entanglement and quantum coherence plays a central role in advancing quantum technologies. In quantum optical light-atom platforms, these two fundamental resources are often associated with a Jaynes-Cummings model description describing the coherent exchange of a photon between an optical resonator mode and a two-level spin. In a generic nonlinear spin-boson system, more photons and more modes will take part in the interactions. Here we consider such a generalization: the two-mode multiphoton Jaynes-Cummings (MPJC) model. We demonstrate how entanglement and quantum coherence can be optimally generated and subsequently manipulated in experimentally accessible parameter regimes. A detailed comparative analysis of this model reveals that nonlinearities within the MPJC interactions produce genuinely non-Gaussian entanglement, devoid of Gaussian contributions, from noisy resources. More specifically, strong coherent sources may be replaced by weaker, incoherent ones, significantly reducing the resource overhead, though at the expense of reduced efficiency. At the same time, increasing the multiphoton order of the MPJC interactions expedites the entanglement generation process, thus rendering the whole generation scheme again more efficient and robust. We further explore the use of additional dispersive spin-boson interactions and Kerr nonlinearities in order to create spin coherence solely from incoherent sources and to enhance the quantum correlations, respectively. As for the latter, somewhat unexpectedly, there is not necessarily an increase in quantum correlations due to the augmented nonlinearity. Towards possible applications of the MPJC model, we show how, with appropriately chosen experimental parameters, we can engineer arbitrary NOON states as well as the tripartite W state.

In quantum information theory, the accurate estimation of observables is pivotal for quantum information processing, playing a crucial role in computational and communication protocols. This work introduces a technique for estimating such objects, leveraging an underutilized resource in the inversion map of classical shadows that greatly refines the estimation cost of target observables without incurring any additional overhead. A generalized framework for computing and optimizing additional degrees of freedom in the homogeneous space of the shadow inversion is given that may be adapted to a variety of near-term problems. In the special case of local measurement strategies, we show feasible optimization leading to an exponential separation in sample complexity versus the standard approach and, in an exceptional case, we give nontrivial examples of optimized postprocessing for local measurements, achieving the same efficiency as the global Cliffords shadows.

We investigate the topological superconductor candidate ${\mathrm{UTe}}_2$ using high-resolution valence-band resonant inelastic x-ray scattering at the U $M_{4,5}$ edges. We observe atomiclike low-energy excitations that support the correlated nature of this unconventional superconductor. These excitations originate from the U $5f^2$ configuration, which is unexpected since the short Te2-Te2 distances exclude Te2 being $2-$. By utilizing the photoionization cross-section dependence of the photoemission spectra in combination with band structure calculations, we infer that the stabilization of the U $5f^2$ configuration is due to the U $6d$ bonding states in the U dimers acting as a charge reservoir. Our results emphasize that the description of the physical properties should commence with a $5f^2$ ansatz.

Light with a complex structure has become a powerful tool in many studies in classical and quantum optics. Here, we introduce a visual representation of light that is structured simultaneously in space, frequency, and polarization in the form of a higher-order Poincaré sphere and describe interesting links to its fundamental counterpart. We leverage the description to show and experimentally generate light possessing all possible polarization states across its spatiospectral shape, which we term spatiospectral Poincaré beams. By extending the powerful description of higher-order Poincaré spheres to the spatiospectral domain, our work will help to gain a deeper understanding and to develop beneficial applications of structured light.

In slowly driven classical systems, work is a stochastic quantity and its probability distribution is known to satisfy the work fluctuation-dissipation relation, which states that the mean and variance of the dissipated work are linearly related. Recently, it was shown that generation of quantum coherence in the instantaneous energy eigenbasis leads to a correction to this linear relation in the slow-driving regime. Here, we go even further by investigating nonclassical features of work fluctuations in setups with more than one system. To do this, we first generalize slow control protocols to encompass multipartite systems, allowing for the generation of quantum correlations during the driving process. Then, focusing on two-qubit systems, we show that entanglement generation leads to a positive contribution to the dissipated work, which is distinct from the quantum correction due to local coherence generation known from previous work. Our results show that entanglement generated during slow control protocols, e.g., as an unavoidable consequence of qubit crosstalk, comes at the cost of increased dissipation.