A Kerr-nonlinear parametric oscillator (KPO) can generate a quantum superposition of two oscillating states, known as a Schrödinger cat state, via quantum adiabatic evolution and can be used as a qubit for gate-based quantum computing and quantum annealing. In this work, we investigate complex dynamics, i.e., chaos, in two coupled nondissipative KPOs at a few-photon level. After showing that a classical model for this system is nonintegrable and consequently exhibits chaotic behavior, we provide quantum counterparts for the classical results, which are quantum versions of the Poincaré surface of section and its lower-dimensional version defined with time integrals of the Wigner and Husimi functions and also the initial and long-term behavior of out-of-time-ordered correlators. We conclude that some of them can be regarded as quantum signatures of chaos, together with energy-level spacing statistics (conventional signature). Thus, the system of coupled KPOs is expected to offer not only an alternative approach to quantum computing but also a promising platform for the study on quantum chaos.

Directed transport of proteins and other molecules in a crowded living cell is often carried out by diffusion at short distances and by motor-driven cargo transport over long distances. Here we demonstrate, by both experiments and theory, that anchored proteins inside the cell can generate a spatially varying and temporally stable potential (free-energy) landscape for intracellular or membrane transport in the mesoscale. By using a micropatterned substrate, we introduce a periodic array of anchored integrins on the basal membrane of cultured Xenopus muscle cells. This patterned array of anchored integrins imposes a periodic potential $U\left(x\right)$ to the lateral motion of nicotinic acetylcholine receptors (AChRs) on the cell membrane. From a thorough analysis of a large volume of AChR trajectories obtained over a wide range of sampling conditions and long durations from 385 cells, we find the trapping potential $U\left(x\right)$ and its effects on the drift velocity $V_x\left(x\right)$ and diffusion coefficient $D_x\left(x\right)$ of AChRs. Our findings suggest that anchored proteins may play an essential role in generating an effective potential landscape to guide molecular motion in the mesoscale ranging from protein trapping and directed motion to enhanced protein-protein interactions over a long range.

Extreme states of matter exist throughout the universe, e.g., inside planetary cores, stars, or astrophysical jets. Such conditions can be generated in the laboratory in the interaction of powerful lasers with solids. Yet, the measurement of the subsequent plasma dynamics with regard to density, temperature, and ionization is a major experimental challenge. However, ultrashort x-ray pulses provided by x-ray free electron lasers (XFELs) allow for dedicated studies, which are highly relevant to study laboratory astrophysics, laser-fusion research, or laser-plasma-based particle acceleration. Here we report on experiments that employ a novel ultrafast method, which allows us to simultaneously access temperature, ionization state, and nanometer scale expansion dynamics in high-intensity, laser-driven, solid-density plasmas with a single x-ray detector. Using this method, we gain access to the expansion dynamics of a buried layer in compound samples, and we measure opacity changes arising from bound-bound resonance transitions in highly ionized copper. The presence of highly ionized copper leads to a temperature estimate of at least 2 million Kelvin already after the first 100 fs following the high-intensity laser irradiation. More specifically, we make use of asymmetries in small-angle x-ray scattering (SAXS) patterns, which arise from different spatial distributions of absorption and scattering cross sections in nanostructured grating samples when we tune an XFEL to atomic resonant energies of copper. Thereby, changes in asymmetry can be connected with the evolution of the plasma expansion and ionization dynamics. The potential of XFEL-based resonant SAXS to obtain three-dimensional ultrafast, nanoscopic information on density and opacity may offer a unique path for the characterization of dynamic processes in high energy density plasmas.

Collective behavior plays a key role in the function of a wide range of physical, biological, and neurological systems where empirical evidence has recently uncovered the prevalence of higher-order interactions, i.e., structures that represent interactions between more than just two individual units, in complex network structures. Here, we study the optimization of collective behavior in networks with higher-order interactions encoded in clique complexes. Our approach involves adapting the synchrony alignment function framework to a composite Laplacian matrix that encodes multiorder interactions including, e.g., both dyadic and triadic couplings. We show that as higher-order coupling interactions are equitably strengthened, so that overall coupling is conserved, the optimal collective behavior improves. We find that this phenomenon stems from the broadening of a composite Laplacian's eigenvalue spectrum, which improves the optimal collective behavior and widens the range of possible behaviors. Moreover, we find in constrained optimization scenarios that a nontrivial, ideal balance between the relative strengths of pairwise and higher-order interactions leads to the strongest collective behavior supported by a network. This work provides insight into how systems balance interactions of different types to optimize or broaden their dynamical range of behavior, especially for self-regulating systems like the brain.

The disjointness of a stabilizer code is a quantity used to constrain the level of the logical Clifford hierarchy attainable by transversal gates and constant-depth quantum circuits. We show that for any positive integer constant $c$, the problem of calculating the $c$-disjointness, or even approximating it to within a constant multiplicative factor, is NP-complete. We provide bounds on the disjointness for various code families, including the Calderbank-Shor-Steane codes, concatenated codes, and hypergraph product codes. We also describe numerical methods of finding the disjointness, which can be readily used to rule out the existence of any transversal gate implementing some non-Clifford logical operation in small stabilizer codes. Our results indicate that finding fault-tolerant logical gates for generic quantum error-correcting codes is a computationally challenging task.

Magnetic materials with competing magnetocrystalline anisotropy and dipolar energies can develop a wide range of domain patterns, including classical stripe domains, domain branching, and topologically trivial and nontrivial (skyrmionic) bubbles. We image the magnetic domain pattern of ${\mathrm{Fe}}_3{\mathrm{Sn}}_2$ by magnetic force microscopy and study its evolution due to geometrical confinement, magnetic fields, and their combination. In ${\mathrm{Fe}}_3{\mathrm{Sn}}_2$ lamellae thinner than 3 $\mu \mathrm{m}$, we observe stripe domains whose size scales with the square root of the lamella thickness, exhibiting classical Kittel scaling. Magnetic fields turn these stripes into a highly disordered bubble lattice. Complementary micromagnetic simulations quantitatively capture the magnetic field and thickness dependence of the magnetic patterns, reveal strong reconstructions of the patterns between the surface and the core of the lamellae, and identify the observed bubbles as skyrmionic bubbles. Our results imply that geometrical confinement together with competing magnetic interactions can provide a path to fine-tune and stabilize different types of topologically trivial and nontrivial spin structures in centrosymmetric magnets.

We present results on the evolution of jets (electrons-positrons and photons) formed in colliding two ultraintense laser pulses with varying frequencies and amplitudes. We focus on the nonlinear dynamics of the seeded electrons in the superposition of the two counterpropagating laser pulses and its implications for the experimentally measurable properties of jets, e.g., angular spectra and widths of the emitted jets, by changing the intensity and frequency of the two colliding laser pulses. We verify our analytical results by doing both Monte Carlo and two-dimensional particle-in-cell simulations.

Random walks serve as important tools for studying complex network structures, yet their dynamics in cases where transition probabilities are not static remain under explored and poorly understood. Here we study nonlinear random walks that occur when transition probabilities depend on the state of the system. We show that when these transition probabilities are nonmonotonic, i.e., are not uniformly biased towards the most densely or sparsely populated nodes, but rather direct random walkers with more nuance, chaotic dynamics emerge. Using multiple transition probability functions and a range of networks with different connectivity properties, we demonstrate that this phenomenon is generic. Thus, when such nonmonotonic properties are key ingredients in nonlinear transport applications complicated and unpredictable behaviors may result.

We experimentally demonstrate a multimode interferometer comprising a Bose-Einstein condensate of ${}^{39}\mathrm{K}$ atoms trapped in a harmonic potential, where the interatomic interaction can be canceled exploiting Feshbach resonances. Kapitza-Dirac diffraction from an optical lattice coherently splits the BEC in multiple momentum components equally spaced that form different interferometric paths, with trajectories closed by the trapping harmonic potential. We investigate two different interferometric schemes, where the recombination pulse is applied after a full or half oscillation in the confining potential. We find that the relative amplitudes of the momentum components at the interferometer output are sensitive to external forces, through the induced displacement of the harmonic potential with respect to the optical lattice. We show how to calibrate the interferometer, fully characterize its output, and discuss perspective improvements.

We report how higher harmonics of collective excitations emerge in a two-dimensional layer of strongly correlated charged microparticles in a complex plasma with a periodically alternating screening. The simulation results of the radio frequency discharge and the charged microparticles are obtained using a highly accurate multiscale and multiphysics approach based on the particle-in-cell technique, Monte Carlo collision calculations, and molecular dynamics simulations. We also devise a simple phenomenological expression for the dispersion relation of higher harmonics. Furthermore, our analysis reveals that the periodically alternating screening causes a self-conjugate state with negative refraction. In doing so, we demonstrate how complex plasmas can serve as a test bed for studying the fundamental physics of a self-conjugate state in strongly correlated systems.

Low-energy dynamics of many-body fracton excitations necessary to describe topological defects should be governed by a novel type of hydrodynamic theory. We use a Poisson bracket approach to systematically derive hydrodynamic equations from conservation laws of scalar theories with fracton excitations. We study three classes of theories. In the first class we introduce a general action for a scalar with a shift symmetry linear in the spatial coordinates, whereas the second one corresponds with a complex scalar, while the third class serves as a toy model for disclinations and dislocations propagating along the Burgers vector. We apply our construction to study hydrodynamic fluctuations around equilibrium states and derive the dispersion relations of hydrodynamic modes.

Electron paramagnetic resonance (EPR) performed with a scanning tunneling microscope (STM) allows for probing the spin excitation of single atomic species with MHz energy resolution. One of the basic applications of conventional EPR is the precise determination of magnetic moments. However, in an STM, the local magnetic fields of the spin-polarized tip can introduce systematic errors in the measurement of the magnetic moments by EPR. We propose to solve this issue by finding tip-sample distances at which the EPR resonance shift caused by the magnetic field of the tip is minimized. To this end, we measure the dependence of the resonance field on the tip-sample distance at different radiofrequencies and identify specific distances for which the true magnetic moment is found. Additionally, we show that the tip's influence can be averaged out by using magnetically bistable tips, which provides a complementary method to accurately measure the magnetic moment of surface atoms using EPR STM.

One of the most promising applications of quantum computing is simulating quantum many-body systems. However, there is still a need for methods to efficiently investigate these systems in a native way, capturing their full complexity. Here we propose variational quantum anomaly detection, an unsupervised quantum machine learning algorithm to analyze quantum data from quantum simulation. The algorithm is used to extract the phase diagram of a system with no prior physical knowledge and can be performed end-to-end on the same quantum device where the system is simulated on. We showcase its capabilities by mapping out the phase diagram of the one-dimensional extended Bose–Hubbard model with dimerized hoppings, which exhibit a symmetry protected topological phase. Further, we show that it can be used with readily accessible devices today by performing the algorithm on a real quantum computer.

Transition-metal oxides provide an excellent platform to generate ground states by tuning the various degrees of freedom via stimuli such as chemical doping. By investigating the electrical, magnetic, and thermodynamic properties of several compositions of the bilayered ${\mathrm{Sr}}_3{\left({\mathrm{Ru}}_{1-x}{\mathrm{Mn}}_x\right)}_2{\mathrm{O}}_7$ with $x$ ≥ 0.36, we complete its $x$-T phase diagram and unveil a spin-glass regime. Upon Mn doping, the ground state of the system changes from the short-range antiferromagnetically (AFM) coupled metal $(0\le x\le 0.05)$ to the E-type AFM-ordered insulator $(0.05<x\le 0.20)$ to the spin-glass insulator $(0.20<x\le 0.66)$ to the canted AFM-ordered insulator $(x\sim 1.0)$. The complex evolution of the magnetic ground state results from the competition between AFM and ferromagnetic (FM) interactions. The peculiar spin-glass state between two long-range magnetically ordered states implies the significance of spin disorder induced by the intermixing of Mn and Ru ions with the lowest transition temperature for Ru : Mn ∼ 1:1 ($x\sim 0.5$).

Gaussian states and measurements collectively are not powerful-enough resources for quantum computing, as any Gaussian dynamics can be simulated efficiently, classically. However, it is known that any one non-Gaussian resource—a state, a unitary operation, or a measurement—together with Gaussian unitaries, makes for universal quantum resources. Photon number resolving (PNR) detection, a readily realizable non-Gaussian measurement, has been a popular tool to try and engineer non-Gaussian states for universal quantum processing. In this paper, we consider PNR detection of a subset of the modes of a zero-mean pure multimode Gaussian state as a means to herald a target non-Gaussian state on the undetected modes. This is motivated from the ease of scalable preparation of Gaussian states that have zero mean, using squeezed vacuum and passive linear optics. We calculate upper bounds on the fidelity between the actual heralded state and the target state. We find that this fidelity upper bound is $1/2$ when the target state is a multimode coherent cat-basis cluster state, a resource sufficient for universal quantum computing. This proves that there exist non-Gaussian states that are not producible by this method. Our fidelity upper bound is a simple expression that depends only on the target state represented in the photon-number basis, which could be applied to other non-Gaussian states of interest.

Laser irradiation of deuterated polyethylene nanowire arrays at intensities of $5\times {10}^{19}\mathrm{W}\mathrm{c}{\mathrm{m}}^{\text{–}2}$ was recently reported to accelerate deuterons to multi-MeV energies, resulting in microscale fusion. Here we show that irradiation of deuterated nanowire targets at intensities of $\sim 3\times {10}^{21}\mathrm{W}\mathrm{c}{\mathrm{m}}^{\text{–}2}$ with high contrast $\lambda =400\mathrm{nm}$ laser pulses of 45 fs duration leads to different plasma dynamics in which the tip of the nanowires rapidly explodes to form an overdense plasma, but the onset of relativistic transparency allows the ultrashort laser pulse to penetrate deep into the nanowire array, enhancing particle acceleration. Experiments and particle-in-cell simulations show that ions are accelerated in the laser beam backward direction to energies up to 13 MeV by a target normal sheath acceleration (TNSA) field that develops in the front of the target, forming collimated beams characterized by full wave at half maximum divergence as low as 7.5°. The simulations also show that deeper within the nanowire array ions are accelerated radially to MeV energies by an internal TNSA field normal to the nanowire surfaces. These radially accelerated deuterons collide with other D atoms, as do those directed toward the $\mathrm{C}{\mathrm{D}}_2$ substrate, leading to D-D fusion reactions. Irradiation with 8 J laser pulses is measured to generate up to $1.2\times {10}^7$ D-D fusion neutrons per shot. The simulations suggest the use of a thinner substrate would also accelerate ions originating from a small area in the back of the target in the laser forward direction.