The decoherence of superpositions of classically distinguishable states (cat states) is crucial for understanding quantum-to-classical transitions and quantum measurements. So far, irreversible decoherence processes of mesoscopic cat states have been demonstrated in several experiments. We here report on an experimental demonstration of the dynamics of such states in a reservoir with controllable degrees of freedom, which allows observation of the transition from reversible to irreversible mesoscopic decoherence. The experiment is performed with a circuit quantum electrodynamics device, where a bus microwave resonator storing a photonic cat state is connected to many nonlinear electronic oscillators. Each of the oscillators that are effectively coupled to the bus resonator serves as one degree of freedom of the reservoir. We characterize the which-path information about the resonator’s state with the distinguishability. The experimental results reveal that the amount of spontaneously erasable which-path information progressively decreases with the increase in the number of the reservoir’s degrees of freedom. When the reservoir contains sufficiently many oscillators, the which-path information acquired by the reservoir cannot be erased by the system-reservoir interaction at later times, which makes the decoherence irreversible. We further characterize the non-Markovianity of such a controllable open mesoscopic system.

Large lepton flavor asymmetries at the QCD epoch could generate a pion condensation phase in the early Universe. For large enough tau lepton flavor asymmetries, the speed of sound can exceed the conformal value, leaving a distinctive imprint on the low-frequency gravitational wave (GW) spectrum from causal sources. Beyond probing the formation of a pion condensation phase, the detection or nondetection of this signature in future pulsar timing arrays (PTAs) datasets would provide a novel constraint on lepton asymmetries in the early Universe. We determine the corresponding GW spectrum and its tilt, comparing them with the standard case of vanishing lepton asymmetry. Finally, we discuss the implications for the stochastic GW background reported by PTAs, using the NANOGrav 15-year dataset.

Nuclear polarization plays an essential role in precision measurements, symmetry tests, and emerging quantum technologies, yet efficient polarization of heavy nuclei remains a major challenge. We propose an efficient, intense-laser-based approach that achieves high-efficiency polarization of heavy nuclei through the nonlinear interaction of circularly polarized femtosecond laser pulses with hydrogenlike ions. This scheme enables rapid transfer of angular momentum from light to the nucleus. Numerical simulations show that a single pulse can generate polarization exceeding 10%, while a pulse sequence can drive the system to near-unity polarization. The method is broadly applicable to heavy ions with large hyperfine splittings, as demonstrated for ${}^{229}\mathrm{Th}$, ${}^{205}\mathrm{Pb}$, and ${}^{209}\mathrm{Bi}$. The ability to produce near-complete polarization of large-spin nuclei and heavy ions opens new avenues for nuclear physics and nucleus-based quantum technologies.

Driven Floquet systems can realize topological phases with no static counterparts. This so-called anomalous Floquet topology breaks the bulk-boundary correspondence based on the Chern number. The number of edge modes in each band gap is instead determined by another integer index, a winding number, which is calculated from the time evolution operator of the bulk states within one driving period. While topological Chern numbers can be inferred from real-space measurements, it is not straightforward to obtain information about the anomalous Floquet topological phase from bulk measurements. Here we consider two-band models and show that the area enclosed during a Floquet period by an initially localized particle signals the presence of an anomalous phase when it approaches half the unit cell area. In general, we show that for dispersionless dynamics during the micromotion, the enclosed area is quantized and an exact proportionality relation exists between the area and the winding number. Direct detection of anomalous topology in real space could be realized in several quantum simulation platforms, and could be useful for systems with disorder or interactions. Building on the connection between area and winding number, we also show a way to realize arbitrarily high winding numbers.

The pair density wave state with eight-unit-cell ($8a_0$) periodicity has been widely regarded as the primary order in cuprates, yet its existence and origin remain subjects of intense debate. Using spectroscopic imaging scanning tunneling microscopy, we observe spatial modulations of the electronic states with approximately $8a_0$ periodicity in both the superconducting and insulating regimes of hole-doped ${\mathrm{Ca}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$ cuprate. We find that the $8a_0$ spatial patterns are generated by the formation of molecular orbitals by doped holes, which organize into $4a_0\times 4a_0$ plaquettes as the basic unit. Our results identify the $4a_0$ molecular-orbital plaquette as the fundamental electronic building block in cuprates, while the $8a_0$ pair density wave represents a spatial subharmonic that emerges at sufficiently high doping.

Antiferromagnet-superconductor (AFM-SC) hybrids offer a rich but largely unexplored platform for realizing spin-triplet Cooper pairing and chiral topological superconductivity, yet experimental demonstrations remain scarce. Here, we report the modification of superconductivity in ${\mathrm{NbSe}}_2/{\text{MnPS}}_3$ heterostructures via the AFM proximity effect. The Néel order of ${\mathrm{MnPS}}_3$ effectively suppresses the Ising superconductivity of ${\mathrm{NbSe}}_2$ and induces a spatially inhomogeneous superconducting state with an inherent junction network. Leveraging this intrinsic Josephson coupling, we observe a finite phase offset in the critical-current interference pattern and a zero-field supercurrent diode effect—two independent signatures of spontaneous time-reversal symmetry breaking. Supported by theoretical modeling, we attribute these emergent phenomena to the proximity-induced stabilization of a subdominant in-plane triplet pairing channel, which is distinct from the intrinsic Ising channel of ${\mathrm{NbSe}}_2$. Our findings establish AFM-SC heterostructures as a versatile platform for exploring nonreciprocal transport and open promising avenues for superconducting spintronics.

At a quantum critical point, the universal scaling behavior of Rényi entanglement entropy is controlled by the universality class of the codimension-two Rényi (or conical) defects in the infrared theory. In this Letter we perform a systematic study of critical correlations along Rényi defect lines in $(2+1)\mathrm{D}$ quantum spin models realizing quantum phase transitions described by the O(3) Wilson-Fisher universality class, using large-scale quantum Monte Carlo simulations. We present numerical evidence that, for a fixed Rényi index $n$, there exist multiple Rényi defect universality classes, with distinct critical exponents for the O(3) order parameter on the defect. These universality classes are realized by choosing microscopically different entanglement cuts in lattice models, which we classify as ordinary, special, and extraordinary according to their relation to surface criticality. For the extraordinary entanglement cut, we further find evidence for a phase transition on the defect as a function of the Rényi index. Our results highlight the key role of defect universality classes in determining the universal scaling of Rényi entanglement entropy, and provide a framework for understanding the previously observed dependence of Rényi entanglement entropy scaling on microscopic lattice details.

Chiral edge states in Chern insulators are theoretically predicted to propagate unidirectionally along the sample boundary with inherent robustness against local perturbations, which manifests as the immunity to impurity-induced backscattering, a key factor for the development of robust, high-performance quantum devices. However, the direct experimental verification of the robustness of chiral edge states remains scarce. Here, we experimentally validate the robustness of the chiral edge states in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ devices by introducing engineered geometric defects via atomic force microscopy (AFM) nanomachining. Specifically, under a moderate perpendicular magnetic field, the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ devices exhibit the Chern insulator state, characterized by a quantized Hall plateau and simultaneously vanishing longitudinal resistance. To verify the robustness of this topological state, we modify the device geometry by creating a structural cut that reaches the substrate using AFM nanomachining. Remarkably, the quantization behavior survives this drastic modification. The robust nature of the chiral edge transport is further confirmed by two-terminal, three-terminal, and nonlocal measurements, demonstrating that the edge currents can survive the engineered cut. Our results provide strong evidence for the robustness of chiral edge states against geometric disruption and establish AFM nanomachining as a promising technique for topological quantum devices engineering.

Ultrathin superconducting (SC) films embedded between two ferromagnetic insulators (FI) experience magnetic-exchange coupling, enabling the switching of the superconducting state by controlling the relative FI magnetization alignment. We investigate micrometer-scale devices patterned from such thin-film heterostructures and demonstrate their reproducible operation as nonreciprocal superconducting memory elements. Single-cell writing is realized using current-pulse-induced, heat-assisted magnetic switching. Furthermore, at a lower temperature, symmetry breaking gives the memory elements a marked nonreciprocity, with zero magnetic field superconducting diode efficiencies exceeding $\pm 60\%$. These results present highly scalable FI/SC/FI hybrid structures as a contender for state-of-the art robust superconducting memories for neuromorphic superconducting computing and new data guiding schemes.

Local molecular orientation and conformation within nanostructures is central to their behavior in devices, emergent quantum states, and biological processes. X-ray microscopy and scattering at the carbon absorption edge is uniquely sensitive to these phenomena, through transition dipole moments encoded with photon energy and polarization. However, quantitative analysis is precluded due to the lack of accurate optical models with bond and orientation specificity. We generate such a model through an unsupervised machine learning algorithm that clusters density functional theory calculations into principle electronic transitions, quantitatively refined with angle-resolved absorbance measurements. The resulting optical tensor reproduces data from samples with domains of different orientation and crystalline packing. This refinement method connects spectral features to chemical moieties and resolves measurement-inaccessible dipole moments, establishing a new paradigm for label-free orientation analyses of bonds within molecular nanostructures.

Microwave-induced resistance oscillations (MIROs) occur when a two-dimensional electron gas is subjected to radiation of frequency $\omega =2\pi f$ and varying magnetic field $B$. MIROs are periodic in $1/B$, with the period determined by the radiation frequency $\omega$, and their amplitude scales with the radiation power. Stepping from single-photon transitions between Landau levels, MIROs are found on the low-field side of the cyclotron resonance, ${\omega }_c\lesssim \omega$, where ${\omega }_{\mathrm{c}}$ is the cyclotron frequency. Here, we report on another class of magneto resistance oscillations, which are induced by high-intensity radiation in the radio frequency range and occur at ${\omega }_c\gg \omega$. These oscillations are independent of frequency $\omega$, they can be either $1/B$ or $1/B^2$ periodic, and their period is controlled by the radiation electric field. We further show that by using a displacement model in the limit of short-range (“sharp”) disorder we can extract the radiation field and the width of the cyclotron resonance.

A measurement of the ratio of semileptonic branching fractions $\mathcal{R}(J/\psi )$, defined as $\mathcal{R}(J/\psi )\equiv \mathcal{B}(B_c^{+}\to J/\psi {\tau }^{+}{\nu }_{\tau })/\mathcal{B}(B_c^{+}\to J/\psi {\mu }^{+}{\nu }_{\mu })$, is reported using a sample of proton-proton collision data corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ recorded by the LHCb experiment in 2016–2018 at a center-of-mass energy of 13 TeV. The measured value is found to be $\mathcal{R}(J/\psi )=0.51\pm 0.12(\mathrm{stat})\pm 0.08(\mathrm{syst})$, which is within 1.8 standard deviations of the predictions from the standard model assuming lepton flavor universality.

Cooperative emission is well understood for idealized symmetric systems, but its fundamental limits in spatially extended, free-space ensembles remain an open question. Here, we derive a universal law for the scaling of the maximum photon emission rate with system size that unifies both ordered arrays and disordered atomic clouds in arbitrary dimensions at fixed density. We demonstrate that, for a fixed atomic density, the maximum emission rate scales universally as the product of the atom number and the system’s geometric optical depth. The geometric optical depth differs from the result of the Beer-Lambert law at high density and encodes the dimensional scaling across all regimes from independent emission to the Dicke limit. Furthermore, we establish a scaling law for directional detection, revealing that the observed rate depends on the detector’s numerical aperture: small apertures yield Dicke-like quadratic scaling, whereas large apertures recover our integrated universal bound. Our results establish optical depth as the parameter governing many-body cooperative emission in both ordered and disordered ensembles, and reveal that directional and total-emission scalings must be carefully distinguished in experimental settings.