Reservoir computing (RC) is a simple and efficient model-free framework for forecasting the behavior of nonlinear dynamical systems from data. Here, we show that there exist commonly-studied systems for which leading RC frameworks struggle to learn the dynamics unless key information about the underlying system is already known. We focus on the important problem of basin prediction—determining which attractor a system will converge to from its initial conditions. First, we show that the predictions of standard RC models (echo state networks) depend critically on warm-up time, requiring a warm-up trajectory containing almost the entire transient in order to identify the correct attractor. Accordingly, we turn to next-generation reservoir computing (NGRC), an attractive variant of RC that requires negligible warm-up time. By incorporating the exact nonlinearities in the original equations, we show that NGRC can accurately reconstruct intricate and high-dimensional basins of attraction, even with sparse training data (e.g., a single transient trajectory). Yet, a tiny uncertainty in the exact nonlinearity can render prediction accuracy no better than chance. Our results highlight the challenges faced by data-driven methods in learning the dynamics of multistable systems and suggest potential avenues to make these approaches more robust.

Strong correlation and topology are two main pillars of modern physics, which can be bridged by fractional quantum Hall states and their lattice analogs known as fractional Chern insulators. A particularly pressing question for fractional Chern insulators is if there exists a lattice analog of the Laughlin state in the 1/3-filled Chern flat band dubbed the Chern-Laughlin state, and if so, how to detect it experimentally. The exact ground state in the 1/3-filled Chern flat band depends on the form of the electron-electron interaction, which can generate various competing ground states derived from, for example, the Laughlin, parafermion, parton, and stripe/nematic states in the 1/3-filled Landau level. In this context, it is of critical importance to precisely identify the exact ground state for a given electron-electron interaction. Here, we propose that the existence of an adiabatic path from the 1/3-filled fractional Chern insulator to the Tao-Thouless state, i.e., the root partition state of the Laughlin state in the thin torus limit, can serve as an effective order parameter for the precise identification of the Chern-Laughlin state. Specifically, by devising a hybrid adiabatic path of first deforming the electron-electron interaction and then taking the thin torus limit, we show that two-dimensional bulk Chern flat bands can host the Chern-Laughlin state at 1/3 filling. More importantly, our results suggest that, unless the electron-electron interaction is strictly of the nearest-neighbor form, the Tao-Thouless state can actually be detected in experiments, for example by using an incommensurate double-walled carbon nanotube made out of the magic-angle twisted bilayer graphene, which allows charge-sensitive surface measurements such as scanning tunneling microscopy. This method can be extended to various other fractional Chern insulators corresponding to both Abelian and non-Abelian fractional quantum Hall states.

Earthquakes are complex physical processes driven by stick-slip motion on a sliding fault. After the main event, a series of aftershocks is usually observed. The latter are loosely defined as earthquakes that follow a parent event and occur within a prescribed space-time window. In seismology, it is currently not possible to establish an unambiguous causal relation between events, and the nearest-neighbor metric is commonly used to distinguish aftershocks from independent events. Here, we employ a soft-glass model as a proxy for earthquake dynamics, previously shown to be able to correctly reproduce the phenomenology of earthquakes, together with a technique that allows us to clearly separate independent and triggered events. We show that aftershocks in our plastic event catalog follow Omori's law with slopes depending on the triggering mode, an observation possibly useful for seismology. Finally, we confirm that the nearest-neighbor metric is indeed effective in separating independent events from aftershocks.

We investigate, using experiments and numerical simulations, the distortions and the alignment of skyrmions in liquid crystal under external flows for a range of average flow velocities. The simulations are based on the Landau-de Gennes $Q$ tensor theory both for isolated as well as for systems with many skyrmions. We found striking flow-driven elongation of an isolated skyrmion and flow alignment of skyrmions in the many-skyrmion system, both of which are also observed in the experiments. In the simulations, particular attention was given to the dissipation rate and to the various dissipation channels for a single skyrmion under external flow. This analysis provides insight on the observed scaling regime of the elongation of isolated flowing skyrmions and revealed a surprising plastic response at very short times, which may be relevant in applications based on the alignment of soft structures such as liquid crystal skyrmions.

Synchronizing a few-level quantum system is of fundamental importance to the understanding of synchronization in the deep quantum regime. Whether a two-level system, the smallest quantum system, can be synchronized has been theoretically debated for the past several years. Here, for the first time, we demonstrate that a qubit can indeed be synchronized to an external driving signal by using a trapped-ion system. By engineering fully controllable gain and damping processes, an ion qubit is locked to the driving signal and oscillates in phase. Moreover, upon tuning the parameters of the driving signal, we observe characteristic features of the Arnold tongue as well. Our measurements agree remarkably well with numerical simulations based on recent theory on qubit synchronization. By synchronizing the basic unit of quantum information, our study opens up the possibility of exploring the application of quantum synchronization to quantum information processing in the near future.

A recent experiment demonstrated that a colloidal heat engine immersed in an active bath can outperform those subject to equilibrium or passive baths. Although it has motivated several theoretical studies to clarify the possible origins of such high efficiency, the discussed noise effects are often intertwined and hard to distinguish in nature. In this paper, we used the optical feedback trap to mimic a colloidal heat engine in various active baths in a precisely controllable setting to analyze the impacts of individual noise properties in real systems. Our experiment, together with theoretical calculations, show that the efficiency of the active engine can be greatly increased when the magnitude of the active-bath noise with a nonzero correlation time is modulated according to the variation of the confining potential in the quasistatic limit. This result reveals how to tune the noise properties of an active bath to enhance the efficiency of a microscopic machine, which could be used to manipulate the functions of stochastic systems under complex active backgrounds.

A chain of magnetic impurities deposited on the surface of a superconductor can form a topological Shiba band that supports Majorana zero modes and holds a promise for topological quantum computing. Yet, most experiments scrutinizing these zero modes rely on transport measurements, which only capture local properties. Here we propose to leverage the intrinsic dynamics of the magnetic impurities to access their nonlocal character. We use linear response theory to determine the dynamics of the uniform magnonic mode in the presence of external ac magnetic fields and coupling to Shiba electrons. We demonstrate that this mode, which spreads over the entire chain of atoms, becomes imprinted with the parity of the ground state and, moreover, can discriminate between Majorana and trivial zero modes located at the ends of the chain. Our approach offers a noninvasive alternative to the scanning tunneling microscopy techniques used to probe Majorana zero modes. Conversely, the magnons could facilitate the manipulation of Majorana zero modes in topological Shiba chains.

Programmable photonic circuits performing universal linear-optical transformations underpin vital functions in photonic quantum information processing, quantum-enhanced sensor networks, machine learning, and many other intriguing applications. Recent advances in photonic integrated circuits facilitate monolithic integration of externally controlled Mach-Zehnder interferometers (MZIs) which can implement arbitrary unitary transformation on a large number of input/output modes. In this work, we demonstrate a $4\times 4$ programmable linear photonic circuit on lithium niobate on an insulator platform employing fast, power-efficient, and low-loss electro-optical phase shifters, showing enormous advantages in terms of configuration rate and power consumption. Our device composed of cascaded MZIs possesses a total on-chip power dissipation of only 1.5 mW when operating at 100 MHz modulation rate. Our MZIs exhibit high bandwidth of 22.5 GHz, fast switching with 160-ps rise time and 120-ps fall time, low insertion loss of 0.15 dB, and on-chip extinction ratio of −34 dB for both cross and bar routes.

Highly polarized, multi-kiloampere-current electron bunches from compact laser-plasma accelerators are desired for numerous applications. Current proposals to produce these beams suffer from intrinsic limitations to the reproducibility, charge, beam shape, and final polarization degree. In this paper, we propose colliding pulse injection (CPI) as a technique for the generation of highly polarized electron bunches from prepolarized plasma sources. Using particle-in-cell simulations, we show that colliding pulse injection enables trapping and precise control over electron spin evolution, resulting in the generation of high-current (multi-kA) electron bunches with high degrees of polarization (up to 95% for $>2\mathrm{kA})$. Bayesian optimization is employed to optimize the multidimensional parameter space associated with CPI to obtain a percent-level energy spread, submicron normalized emittance electron bunches with 90% polarization using 100-TW class laser systems.

Spin-orbit coupling driven by broken inversion symmetry ($I$) is known to lead to unusual magnetic response of superconductors, including extremely large critical fields for spin-singlet superconductors. This unusual response is also known to appear in materials that have $I$, provided there is local $I$-breaking: fermions participating in superconductivity reside on crystal sites that lack $I$. Here we show that this unusual response exists even when the crystal sites preserve $I$. Indeed, we argue that the symmetry of Kramers degenerate fermionic pseudospin is more relevant than the local crystal site symmetry. We examine and classify nonsymmorphic materials with momentum space spin-textures that exhibit an anomalous pseudospin with different symmetry properties from usual spin-1/2. Since this anomalous pseudospin does not depend on the existence of local $I$-breaking crystal sites, and since it optimizes the unusual magnetic response traditionally associated with locally noncentrosymmetric superconductors, it dramatically extends the range of relevant materials. We further show that this anomalous pseudospin leads to fully gapped “nodal” superconductors and provides additional insight into the breakdown of Blount's theorem for pseudospin triplet superconductors. We apply our results to ${\mathrm{UPt}}_3, {\mathrm{BiS}}_2$-based superconductors, Fe-based superconductors, and paramagnetic UCoGe.

The observation, design, and analysis of meshlike networks in bionics, polymer physics, and biological systems has brought forward an extensive catalog of fascinating structures of which a subgroup share a particular, yet critically under appreciated attribute: being embedded in space such that one would not be able to pull them apart without prior removal of a subset of edges, a state which we here call ensnarled. In this study we elaborate on a graph-theoretical method to analyze ensnarled finite, 2-component nets on the basis of Hopf-link identification. Doing so we are able to construct an edge priority operator $\mathit{\Lambda }$, derived from the linking numbers of the spatial graphs' cycle bases, which highlights critical edges. On its basis we developed a greedy algorithm which identifies optimal edge removals to achieve unlinking, allowing for the establishment of a topological metric characterizing the state of ensnarled network pairs.

An open challenge in physics is to expand the frontiers of the validity of quantum mechanics by evidencing nonclassicality of the center of mass state of a macroscopic object. Yet another equally important task is to evidence the essential nonclassicality of the interactions which act between macroscopic objects. Here we introduce a new tool to meet these challenges: massive spatial qubits. In particular, we show that if two distinct localized states of a mass are used as the $|0\rangle$ and $|1\rangle$ states of a qubit, then we can measure this encoded spatial qubit with a high fidelity in the ${\sigma }_x,{\sigma }_y$, and ${\sigma }_z$ bases simply by measuring its position after different duration of free evolution. This technique can be used reveal the irreducible nonclassicality of the spin and center of mass entangled state of a nanocrystal implying macrocontextuality. Further, in the context of Casimir interaction, this offers a powerful method to create and certify non-Gaussian entanglement between two neutral nano-objects. The entanglement such produced provides an empirical demonstration of the Casimir interaction being inherently quantum.

Multiply quantized vortices (MQVs) within single-component Bose-Einstein condensates are unstable and decay rapidly. We show that MQVs can be stabilized by adding a small number of atoms of a second species to the vortex cores, and that these atoms remain in the vortex core as the system evolves. A consequence of the stabilization is that nearby corotating vortices can orbit in the opposite sense to their individual rotations when enough of the second species is present. This has implications concerning the imaging of vortices, as well as quantum turbulence and vortex nucleation in two-component condensates, such as those involving mixtures of ${}^{87}\mathrm{Rb}$ and ${}^{133}\mathrm{Cs}$.

Artificial nanostructures, fabricated by placing atoms or molecules as building blocks in well-defined positions, are a powerful platform in which quantum effects can be studied and exploited. In particular, they offer the opportunity to reduce the electronic interaction between large aromatic molecules and the underlying metallic substrate, if the manipulation capabilities of scanning tunneling microscopy to lift the molecule into an upright geometry on a pedestal of two metal atoms are used. Here, we report a strategy to study this interaction by investigating the Kondo effect. Measurements at millikelvin temperatures and in magnetic fields reveal that this bottom-up assembled standing metal-molecule nanostructure has an $S=1/2$ spin which is screened by substrate electrons, resulting in a Kondo temperature of only $291\pm 13$ mK. We extract its Landé $g$ factor and its exchange coupling $J\rho$ to the substrate, using a third-order perturbation theory in the weak-coupling and high-field regimes. We also show that the interaction between the scanning tunneling microscope tip and the molecule can tune the exchange coupling.

We propose a platform for observing the Josephson diode effect: the Andreev molecule. This nonlocal electronic state is hosted in circuits made of two closely spaced Josephson junctions, through the hybridization of the Andreev states. The Josephson diode effect occurs at the level of one individual junction while the other one generates the required time-reversal and spatial-inversion symmetry breaking. We present a microscopic description of this phenomenon based on fermionic Andreev states, focusing on single channels in the short limit, and we compute both supercurrent and energy spectra. We demonstrate that the diode efficiency can be tuned by magnetic flux and the junctions' transmissions and can reach $45\%$. Going further, by analyzing the Andreev spectra, we demonstrate the key role played by the continuum, which consists of leaky Andreev states and is largely responsible for the critical current asymmetry. On top of proposing an experimentally accessible platform, this work elucidates the microscopic origin of the Josephson diode effect at the level of the fermionic Andreev states.

Quantum theory allows the traversing of multiple channels in a superposition of different orders. When the order in which the channels are traversed is controlled by an auxiliary quantum system, various unknown parameters of the channels can be estimated by measuring only the control system, even when the state of the probe alone would be insensitive. Moreover, increasing the dimension of the control system increases the number of simultaneously estimable parameters, which has important metrological ramifications. We demonstrate this capability for simultaneously estimating both unitary and noise parameters, including multiple parameters from the same unitary such as rotation angles and axes and from noise channels such as depolarization, dephasing, and amplitude damping in arbitrary dimensions. We identify regimes of unlimited advantages, taking the form of $p^2$ smaller variances in estimation when the noise probability is $1-p$, for both single and multiparameter estimations when using our schemes relative to any comparable scheme whose causal order is definite.