We theoretically investigate the resonant and higher order magnetic responses of a collinear antiferromagnet induced by Néel spin-orbit torques (NSOTs). By deriving the dynamical susceptibilities up to the third harmonic, we find remarkable NSOT-induced amplifications of the linear and nonlinear magnetic dynamics by orders of magnitude compared to conventional spin-orbit torques, enabling highly efficient frequency conversion in the terahertz frequency range. From the effective dynamics, we uncover the strong coupling between the Néel vector and the driving field of NSOTs, providing a physical explanation of the gigantic responses at all orders. We then propose a multilayer antiferromagnetic nanodevice leveraging the gigantic harmonic generation to achieve unprecedented frequency amplifiers and converters. Our Letter uncovers a previously overlooked role of the NSOTs in nonlinear dynamics.

Tensor network machine learning models have shown remarkable versatility in tackling complex data-driven tasks. Despite their promising performance, a comprehensive understanding of the underlying assumptions and limitations of these models is still lacking. Here we focus on the rigorous formulation of their no-free-lunch theorem, which is essential yet notoriously challenging to formalize for specific tensor network learning models. In particular, we rigorously analyze the generalization risks of learning target output functions from input data encoded in tensor network states. We first prove a no-free-lunch theorem for machine learning models based on matrix product states. Then we circumvent the challenging issue of calculating the partition function for a two-dimensional Ising model, and prove the no-free-lunch theorem for the case of two-dimensional projected entangled-pair states, by introducing the combinatorial method associated to the “puzzle of polyominoes.” In addition, we rigorously establish an adversarial theorem that emerges naturally as a practical consequence of our no-free-lunch theorem. Our findings reveal the intrinsic limitations of tensor-network-based learning models in a rigorous fashion, and open up an avenue for future analytical exploration of both the strengths and limitations of quantum-inspired machine learning frameworks.

The correlations of certain entangled states can be perfectly simulated classically via a local model. Hence such states are termed Bell local, as they cannot lead to Bell inequality violation. Here, we show that Bell nonlocality can nevertheless be activated for certain Bell-local states via a catalytic process. Specifically, we present a protocol where a Bell-local state, combined with a catalyst, is transformed into a Bell-nonlocal state while the catalyst is returned exactly in its initial state. Importantly, this transformation is deterministic and based only on local operations. Moreover, this procedure is possible even when the state of the catalyst is itself Bell local, demonstrating a new form of superactivation of Bell nonlocality, as well as an interesting form of quantum catalysis. On the technical level, our main tool is a formal connection between catalytic activation and many-copy activation.

Quantum state complexity metrics, such as anticoncentration and nonstabilizerness, offer key insights into many-body physics, information scrambling, and quantum computing. Anticoncentration and equilibration of magic resources under dynamics of random quantum circuits occur at times scaling logarithmically with system size. Here, we examine these phenomena in one-dimensional ergodic Floquet models and thermalizing Hamiltonian systems. Using participation and stabilizer entropies to probe anticoncentration and magic resources, we reveal significant differences between the two settings. Floquet systems align with random circuit predictions, exhibiting anticoncentration and magic saturation at timescales logarithmic in system size. In contrast, Hamiltonian dynamics deviate from the random circuit predictions and require times scaling approximately linearly with system size to achieve saturation of participation and stabilizer entropies, which remain smaller than that of the typical quantum states even in the long-time limit. Our findings establish the phenomenology of participation and stabilizer entropy growth in generic many-body systems and emphasize the role of conservation laws in constraining anticoncentration and magic dynamics.

Quantum error correction (QEC) protects quantum systems against inevitable noises and control inaccuracies, providing a pathway toward fault-tolerant (FT) quantum computation. Stabilizer codes, including surface code and color code, have long been the focus of research and have seen significant experimental progress in recent years. Recently proposed time-dynamical QEC, including Floquet codes and generalized time-dynamical code implementations, opens up new opportunities for FT quantum computation. By employing a periodic schedule of low-weight parity checks, Floquet codes can generate additional dynamical logical qubits, offering enhanced error correction capabilities and, potentially, higher code performance. Here, we experimentally implement the Floquet-Bacon-Shor code on a superconducting quantum processor. We encode a dynamical logical qubit within a $3\times 3$ lattice of data qubits alongside a conventional static logical qubit. We demonstrate FT encoding and measurement of the two-qubit logical states and stabilize these states using repeated error detection. We showcase universal single-qubit logical gates on the dynamical qubit. Furthermore, by implementing a logical controlled-not (cnot) gate, we entangle the dynamical and static logical qubits, generating an error-detected logical Bell state with a fidelity of 75.9%. Our results highlight the potential of Floquet codes for resource-efficient FT quantum computation.

We numerically study ${\mathbb{Z}}_N$ lattice gauge theories in 4D as prototypical models of systems with ${\mathbb{Z}}_N$ 1-form symmetry. For $N\ge 3$, we provide evidence that such systems exhibit not only the expected phases with spontaneously broken/restored symmetry but also a third photon phase. When present, the 1-form symmetry provides a precise notion of confinement, and it is commonly believed that confinement ensues due to the proliferation of extended, stringlike objects known as center vortices, which carry a ${\mathbb{Z}}_N$ flux. However, this picture is challenged by the three-phase scenario investigated here. We show that both the confined and the photon phases are associated with the proliferation of center vortices and that the key difference between them lies in whether or not vortex junctions—the monopoles— proliferate.

We report nuclear charge radii for the isotopes ${}^{104–134}\mathrm{Sn}$, measured using two different collinear laser spectroscopy techniques at ISOLDE-CERN. These measurements clarify the archlike trend in charge radii along the isotopic chain and reveal an odd-even staggering that is more pronounced near the $N=50$ and $N=82$ shell closures. The observed local trends are well described by both nuclear density functional theory and valence space in-medium similarity renormalization group calculations. Both theories predict appreciable contributions from beyond-mean-field correlations to the charge radii of the neutron-deficient tin isotopes. The models, however, fall short of reproducing the magnitude of the known $B(E2)$ transition probabilities, highlighting the remaining challenges in achieving a unified description of both ground-state properties and collective phenomena.

The Sn isotopic chain, exhibiting double shell closures at ${}^{100}\mathrm{Sn}$ and ${}^{132}\mathrm{Sn}$, is a key testing ground for theoretical models of the atomic nucleus. It was originally predicted that the transitional matrix elements between the first $2^{+}$ state and the $0^{+}$ ground state for the even-even isotopes in this chain should show a simple dependence on the neutron number. This prediction was, however, disproven experimentally in some of the first experiments with postaccelerated radioactive beams, a situation that has remained unresolved ever since. Subsequent theoretical work has suggested that the explanation can be found in proton excitations across the $Z=50$ shell gap, with an accompanying experimental signature that the first excited $2^{+}$ state in ${}^{110}\mathrm{Sn}$ should have a distinct oblate shape. In this Letter, we present the first measurements of the spectroscopic quadrupole moment of the $2_1^{+}$ state, $B(E2;4_1^{+}\to 2_1^{+})$ and $B(E2;4_2^{+}\to 2_1^{+})$ values for ${}^{110}\mathrm{Sn}$, as well as the $B(E2;2_1^{+}\to 0_1^{+})$ value with significantly improved precision compared to previous results. From the same experiment, half-lives of the $2_1^{+}$ and $4_1^{+}$ states were measured using the Doppler shift attenuation method. Our combined result, $Q(2_1^{+})=20(8){\mathrm{efm}}^2$ for ${}^{110}\mathrm{Sn}$, is the largest positive value known among the Sn isotopes, indicating an oblate shape of the state by more than $2\sigma$. Comparison of the $E2$ transition strengths and quadrupole moments with recent shell model calculations are presented.

Excited states in the proton drip line nucleus ${}^{61}\mathrm{Ga}$ were populated via the fusion-evaporation reaction ${}^{24}\mathrm{Mg}({}^{40}\mathrm{Ca},p2n){}^{61}\mathrm{Ga}$. The experimental setup at Argonne National Laboratory comprised a novel combination of the Gammasphere array with two CD-shaped double-sided Si-strip detectors inside the Microball CsI(Tl) charged-particle detection array, as well as the Neutron-Shell liquid scintillators and the Fragment Mass Analyzer. Owing to the setup’s unprecedented in-beam proton spectroscopy and tracking capabilities, a coincidence between a 957.6(5)-keV $\gamma$ ray and a 1.876(24)-MeV proton line was observed, which identifies the quasibound proton $\pi g_{9/2}$ single-particle state in ${}^{61}\mathrm{Ga}$ at $E_x=2150(34)\mathrm{keV}$. This probes isospin symmetry at the limit of nuclear binding by providing a unique challenge for the shell-model interpretation of mirror nuclei beyond doubly magic ${}^{56}\mathrm{Ni}$.

We clarify how the weak-interaction-driven bulk viscosity $\zeta$ and the bulk relaxation time ${\tau }_{\mathrm{\Pi }}$ of neutrino-transparent $npe$ matter depend on the nuclear symmetry energy. We show that, at saturation density, the equation-of-state dependence of these transport quantities is fully determined by the experimentally constrained nuclear symmetry energy $S$ and its slope $L$. Variations of $L$ can change the bulk viscosity by orders of magnitude, which can affect both the dissipative and the conservative tidal response of neutron stars. This suggests that both conservative and dissipative effects encoded in the gravitational-wave signatures of binary neutron star inspirals may help constrain nuclear symmetry-energy properties.

We demonstrate Doppler broadening thermometry (DBT) with all-frequency-domain measurements. Using the R(10) transition of CO at 1567 nm in a high-finesse optical cavity (mode width 0.6 kHz), we resolve Doppler profiles with high signal-to-noise ratios across 2–17 Pa pressures. A global Voigt-profile analysis yields temperatures deviating by only $-2.0\pm 3.6\mathrm{mK}$ from calibrated thermometers, with systematic errors suppressed below 9 ppm. The results show negligible dependence on line-shape models when accounting for pressure effects, resolving a long-standing challenge in DBT. This approach establishes a new paradigm for quantum-based thermometry and provides a precision platform for testing molecular collision physics.

Ultraintense pulses from x-ray free-electron lasers can drive, within femtoseconds, multiple processes in the inner shells of atoms and molecules in all phases of matter. The ensuing complex ionization pathways of outer-shell electrons from the neutral to the final highly charged states make a comparison with theory enormously difficult. We resolve these pathways by preparing highly charged ions in an electron beam ion trap before exposing them to the pulsed radiation. This reveals how relativistic fine-structure effects shift electronic energies, largely compensate the core-screening potential, and enable the consecutive, resonant absorption of two quasi-monochromatic x-ray photons that would generally be unfeasible. This doubly resonant channel enhances the efficiency of two-photon ionization by more than two orders of magnitude, dominating in this regime the nonlinear interaction of light and matter with possible application for future precision x-ray metrology.

We experimentally demonstrate background-free, hyperfine-level-selective measurements of individual Cs atoms by simultaneous cooling to $5.3\mathrm{\mu }\mathrm{K}$ and imaging on the $6s_{1/2}\to 5d_{5/2}$ electric-quadrupole transition. We achieve hyperfine-resolved detection with fidelity 0.9993(4) and atom retention of 0.9954(5), limited primarily by vacuum lifetime. Performing state measurements in a 3D cooling configuration enables repeated low loss measurements. A theoretical analysis of an extension of the demonstrated approach, based on quenching of the excited state with an auxiliary field, identifies parameters for hyperfine-resolved measurements with a projected fidelity of $\sim 0.9995$ in $\sim 60\mathrm{\mu }\mathrm{s}$.

We introduce the concept of giant superatoms (GSAs), where two or more interacting atoms are nonlocally coupled to a waveguide through one of them, and explore their unconventional quantum dynamics. For braided GSAs, this setup enables decoherence-free transfer and swapping of their internal entangled states. For separate GSAs, engineering coupling phases leads to state-dependent chiral emission, which enables selective, directional quantum information transfer. This mechanism further facilitates remote generation of $W$-class entangled states. Our results thereby open exciting possibilities for quantum networks and quantum information processing.

Entangled photons carry nontrivial quantum correlations that defy classical physics and provide new tools for monitoring quantum dynamics in molecules. The use of low-flux entangled photons in molecular spectroscopy has been proposed in the past to probe excited-state dynamics with enhanced temporal and spectral resolutions. However, these techniques have been challenging to implement experimentally since the resulting signal has a low signal-to-noise ratio. The signal strength can be boosted by using intense entangled-photon beams, where multiple pairs of entangled photons are present in the environment. This allows the molecule under study to interact with both entangled and unentangled photons, where the classical component of the spectroscopic signal stemming from the latter can mask the spectral features associated with the former. In this Letter, we show how the signal arising from unentangled photons can be eliminated when intense entangled-photon beams are used in two-dimensional electronic spectroscopy (2DES), and demonstrate the advantage of photonic entanglement.