Optical cycling refers to repeated excitation and spontaneous emission on an electronic transition in an atom or molecule. Optical cycling in molecules can enable a wide range of quantum control and readout techniques, but unfortunately it has only been demonstrated on a small class of alkalilike or alkaline-earth-like molecules. Thorium monoxide (ThO), a molecule used in one of the most precise permanent electron electric dipole moment (eEDM) searches (ACME†) [Andreev et al., Nature (London) 562, 355 (2018)], does not fall into this category. In this work, we demonstrate the first optical cycling on this nonconventional class over a range of experimental parameter space, including laser intensity, polarization switching rate, and interaction time. We show that both the $J=1$ and $J=2$ rotational levels of ThO molecule are capable of cycling an average of 11(2) photons with a single laser, at scattering rates of $1.9\left(6\right)\times {10}^6$ and $2.3\left(7\right)\times {10}^6 {\mathrm{s}}^{-1}$, respectively, before population is lost to other vibronic levels. We outline a scheme to apply this demonstrated optical cycling in an ACME-style eEDM measurement, improving the detection efficiency by over fourfold compared to noncycling fluorescence detection. This would lead to over a twofold enhancement in the statistical sensitivity of the eEDM search. This optical-cycling scheme can be further extended to scatter $\sim 100$ photons, which would enable a wider range of quantum control and sensing using ThO molecules.

We demonstrate a model-free data analysis framework that leverages escort-weighted Shannon entropy and several divergence matrices to detect phase transitions in scattering and imaging datasets. By establishing a connection between physical entropy and informational entropy, this approach provides a sensitive method for identifying phase transitions without a physical model or order parameter. We further show that pairwise divergence matrices, in particular, Kullback-Leibler divergence, Jeffrey divergence, Jensen-Shannon divergence, and difference Kullback-Leibler divergence, provide more comprehensive measures of statistical changes than scalar entropy alone. Our approach successfully detects the onset of both long- and short-range order in neutron and x-ray scattering data, as well as a nontrivial phase transition in magnetic skyrmion lattices observed through Lorentz-transition electron microscopy. These results establish a framework for fast, automated, model-free detection of physical order in experimental data with broad applications in materials science and condensed matter physics.

We present an ab initio framework for computing inelastic electron scattering (IES) on isolated molecules and in condensed phases, focusing on liquid water as a prototypical target. Our method employs a pseudocontinuum treatment for electron-impact ionization. The scattered projectile is described by a plane wave, while the final states of the target, including the excited or ejected electron, are expanded in a square-integrable basis. This approach naturally describes the transition between the excitation and ionization regimes and enables molecular-hole-resolved IES cross sections to be extracted within a standard quantum-chemistry framework. For isolated water molecules, the computed IES cross sections agree with available experimental data. For liquid water, our calculations show that solvation has a small effect on the total IES cross section. We see, however, that the liquid environment leads to a substantial enhancement of electron-impact-induced ionization and a corresponding reduction of electron-impact-induced excitation. We discuss the total and hole-resolved single differential cross sections, offering a complete molecular picture of IES and paving the way toward a detailed simulation of radiation-damage formation in water.

Spin amplification is the process that ideally increases the number of excited spins when one of them is excited initially. We show that by applying optimal control techniques to design classical drive pulse shapes, spin amplification can be achieved in a previously unexplored fast regime, with amplification times comparable to the intrinsic interaction timescale. This is an order of magnitude faster than the previous protocols and makes spin amplification possible even with significant decoherence and inhomogeneity in the spin system. The initial spin excitation can be delocalized over the entire ensemble, which is a more typical situation when a photon is collectively absorbed by the spins. We focus on the superconducting persistent-current artificial atoms and the Rydberg atoms as spins.

We study the thermodynamic performance of a periodic quantum Otto cycle operating on the single-impurity Anderson model. Using a decomposition of the time-evolution generator based on the principle of minimal dissipation, combined with the numerically exact hierarchical equations of motion method, we analyze the operating regimes of the quantum thermal machine and investigate effects of Coulomb interactions, strong system-reservoir coupling, and energy level alignments. Our results show that Coulomb interaction can change the operating regimes and may lead to an enhancement of the efficiency.

Understanding how frustration and symmetry breaking shape collective behavior is a central problem in quantum many-body systems. In this work, we investigate this problem in large one- and two-dimensional arrays of coupled Dicke models on a periodic lattice, where strong light-matter coupling gives rise to a superradiant phase and competition between neighboring order parameters induces spontaneous translational symmetry breaking. Such Dicke lattice models constitute a fundamentally new class of quantum many-body systems, as they simultaneously realize the thermodynamic limit associated with the lattice size and an intrinsic thermodynamic limit arising from collective on-site interactions with quantum emitters. We show that frustration drives photonic density-wave ordering, and that the resulting broken periodicity can be predicted from the excitation spectrum of the symmetric phase, without requiring computationally prohibitive thermodynamic energy minimization. Furthermore, we demonstrate that an emergent Nambu-Goldstone mode arises near the critical point in a one-dimensional chain despite the presence of only discrete symmetry, and uncover the mechanism that enables this otherwise forbidden gapless excitation. We also find quasiperiodic ordering in the superradiant phase, reminiscent of quasicrystals, and demonstrate that synthetic magnetic flux provides a powerful knob to control the nature of translational symmetry breaking. Our results establish a direction in quantum many-body physics where the coexistence of local and global thermodynamic limits gives rise to unconventional symmetry breaking and emergent collective behavior.

We introduce the concept of a global effective fluctuation-dissipation relation for thermal particle motion in heterogeneous and disordered systems. The relation connects two effective quantities: the diffusivity, determined from the long-time scaling of the particle mean-square displacement at thermal equilibrium, and the effective friction factor, associated with the linear scaling of the particle terminal velocity in the presence of a constant external force with the intensity of the force itself. The global effective fluctuation-dissipation relation is identically fulfilled by hydromechanic models of fluid-particle interactions in heterogeneous media, i.e., whenever the friction factor either is a function of the particle position or represents a stochastic process. Conversely, models in which heterogeneity is described via a potential landscape do not fulfill this property in general but solely in the limit of small external forces or small intensities of the equilibrium potential.

Distinct strong-field fragmentation pathways can converge to identical final products in polyatomic molecules, making the underlying reaction dynamics difficult to identify. In methane, Jahn-Teller symmetry breaking after ionization creates distinct intermediate geometries that lead to different three-body routes within the same final fragments. Using delay-dependent, coincidence-resolved momentum correlations in pump-probe Coulomb-explosion imaging, we discriminate fragmentation pathways within the ${\mathrm{CH}}_2^{+}+{\mathrm{H}}^{+}+{\mathrm{H}}^{+}$ channel. We discover a delay-dependent sequential pathway with a transient ${\mathrm{H}}_2$ fragment, characterized by symmetric proton-proton correlations, and separate it from an asymmetric sequential route and concerted fragmentation. Our results establish that delay-resolved coincidence mapping can disentangle intermediate-mediated fragmentation pathways even within an identical three-body final state, and show that in methane such pathways are seeded by Jahn-Teller-driven symmetry breaking.

A classical particle under spatial constraints is strictly confined to live on a specific space manifold or path, but this assumption is incompatible with the zero-point fluctuations of a quantum particle. One way to treat quantum mechanics under constraints is the confinement potential approach (CPA). For a nonrelativistic particle, the CPA maps the problem onto the solution of a Schrödinger-type equation in an isometrically embedded Riemannian submanifold of Euclidean space while the motion along orthogonal directions is decoupled and spatially confined. This approach respects quantum uncertainty, and one of its key results is the appearance of geometry- and metric-induced potentials that affect the stationary states and the dynamics of the particle. For particles constrained to different spaces, such as structures hosting sharp bends, vertices, wedges, conical apices, tips, or self-intersections, a formalism beyond the CPA is needed. Here, a step toward a CPA extension for irregular spaces is presented. After classifying the possible geometric irregularities concerning the CPA formalism, the presentation is focused on a sharply bent quantum wire modeled as an embedded curve with singular (but absolutely integrable) curvature. For a subclass fulfilling the additional requirement that the geometric potential is a distribution of first order, a solution scheme for the confined Schrödinger equation is presented based on singular Sturm-Liouville theory and operator theoretic methods. The analytical considerations and numerical simulations evidence the existence of curvature-induced bound states with nondifferentiable wave functions localized around the singular point, with an extension well beyond the singularity. Furthermore, a multitude of scattering states appear that may affect the transport and optical properties of the system.

We report that optical quasisymmetry groups emerge from the commutation between mirror operation and spin-orbit interaction (SOI) of light. Contrary to the principle of symmetry inheritance in free-space optics—where the symmetry of any structured field is strictly constrained by that of its source—we show that strong SOI enables quasi-symmetry-protected formation of topological lattices even when the underlying optical sources violate the nominal rotational symmetry. By analyzing the Hermiticity of the electric-dipole radiation amplitude in a circular polarization basis, we derive an effective mirror operator acting only on a subset of $C_3$ polarized dipole emitters, forming a quasisymmetry group that commutes with SOI. This quasisymmetry guarantees exact $C_3$ merons and gives rise to a robust polarization zone within which continuously varying input polarizations generate identical topological textures. Our work establishes quasisymmetry as a fundamental principle in optical physics and opens pathways to engineered topological structures of light beyond conventional symmetry constraints.

We study the correlated ground states of twisted mono-bilayer graphene with and without proximity-induced spin-orbit coupling (SOC) from a transition-metal dichalcogenide layer placed on top. We perform self-consistent Hartree-Fock calculations that allow the variational space to include multi-$Q$ translational-symmetry-broken states for all integer and half-integer fillings of the conduction bands, where signatures of correlated, topological states have been reported experimentally. We find interaction-induced insulators that retain moiré translational symmetry at integer fillings, but that break this symmetry at half-integer fillings. We argue that translational symmetry breaking arises from half-filled polarized bands, even when SOC is present. Yet, we find that small SOC can already crucially affect the spin nature of correlated states. Generally, Ising SOC favors out-of-plane spin polarization and spin-valley locking, while Rashba SOC favors in-plane spin order. If only one of these two terms is present, we find that, depending on the type of SOC, it drives a transition from a tetrahedal antiferromagnet to either a coplanar, noncoplanar, or collinear spin-density wave state for half-integer fillings. The frustration associated with the simultaneous presence of both types of SOC can induce chiral, noncoplanar order in parameter ranges where the ground state in the absence of SOC is collinear.

Secure, repeatable access to information stored in deep electron traps remains the central barrier to realizing the full potential of electron-trapping phosphors in next-generation optical memory. Existing readout methods typically rely on destructive thermal or nonselective optical stimulation, which limits repeated access and compromises data integrity. Here, we introduce photonically engineered trap transfer (PETT), a heat-free, nonvolatile approach enabling selective data extraction from deep traps. A specially designed garnet phosphor, $\mathrm{G}{\mathrm{d}}_3\mathrm{G}{\mathrm{a}}_5{\mathrm{O}}_{12}$ codoped with $\mathrm{C}{\mathrm{r}}^{3+}$ and $\mathrm{E}{\mathrm{u}}^{3+}$, serves as the storage medium, with $\mathrm{C}{\mathrm{r}}^{3+}$ acting as the luminescent center and $\mathrm{E}{\mathrm{u}}^{3+}$ engineering a hierarchical trap landscape. Data writing is achieved through an up-conversion charging process that embeds data within 0.01 s. In the PETT readout, visible light transfers electrons from deep to shallow traps; subsequent infrared stimulation releases them, producing a detectable luminescence signal. Kinetic modeling of the PETT process describes the time evolution of the shallow-trap population and reveals its characteristic rise-and-decay behavior. This method provides a reliable, selective, and repeatable route to data retrieval and establishes a robust physical framework for secure, multilevel, rewritable optical memory.

Altermagnetism has emerged as a promising ingredient for realizing nontrivial Josephson phases but so far explored in single Josephson junctions. In this work, we consider the coherent coupling of two Josephson junctions with spin-singlet $s$-wave superconductivity and demonstrate that $d$-wave altermagnetism gives rise to spin-polarized Andreev molecules due to the hybridization of Andreev bound states of each junction when the coupling is weak. Interestingly, these spin-polarized Andreev molecules induce anomalous nonlocal Josephson effect, where the current flow across one Josephson junction due to phase changes across the other junction develops $0-\pi$ and ${\varphi }_0$ transitions originating from altermagnetism. Furthermore, the nonlocal Josephson current carried by spin-polarized Andreev molecules exhibits nonreciprocal critical currents, enabling a nonlocal Josephson diode effect whose polarity is tunable by the altermagnetic strength and right phase. Our findings put forward altermagnetism as a promising arena for designing nonlocal spin Josephson phenomena.

Characterizing the ultimate rates of entanglement distribution is essential for both foundational research and the practical deployment of quantum technologies. To investigate these limits, we introduce an erasure-Pauli channel model describing the distribution of polarization entanglement in optical fiber. For this channel, we derive bounds on the rates of entanglement distribution and related quantum resources under optimal local operations and two-way classical communication (two-way assisted capacities). This framework allows us to determine the optimal repeaterless performance achievable over realistic optical fibers affected by polarization mode dispersion, thereby providing a rigorous benchmark for long-distance polarization-based quantum communication. Finally, we show that both our model and capacity bounds remain robust under the inclusion of detector dark counts.

We explore the interplay between security and key rate of a quantum key distribution (QKD) protocol. This fundamental trade-off is investigated both at the link layer, i.e., for a QKD protocol implemented on a channel, and at the network layer, i.e., within the context of a multiuser multihop communication network. In the former scenario, we consider both discrete- and continuous-variable protocols in the composable finite-size framework, showing how their epsilon security restricts the key rate achievable on a single fiber link under various assumptions for the process of parameter estimation. In the latter scenario, we analyze the impact of composable security in the network setting, studying the interplay between end-to-end (ETE) epsilon security and ETE key rate for arbitrarily chosen remote end points. Starting from basic topologies to more complex ones, such as perturbed lattices, we analyze this trade-off under different types of routing strategies. In multipath routing, a greater number of paths can improve key rates, but this enhancement is accompanied by a reduction in the ETE security level. In the setting of single-path routing, we introduce a modified Dijkstra algorithm, which we call “lambda protocol,” able to optimize route construction depending on the joint ETE demand for security and rate. Our results are first derived for specific network instances (i.e., fixed topologies within a given network class) and subsequently extended to ensemble averages over entire network classes, where phase transitions are revealed with respect to node connectivity.

It is generally argued that Mermin-Wagner theorem excludes the possibility of long-range order in two-dimensional bosonic systems at nonzero temperatures. In contrast, we show here that generic bilayer semiconductors could demonstrate true Bose-Einstein condensation of interlayer excitons. We find that the key requirements include (1) reduction of the interlayer band gap using an applied electric field so that excitons spontaneously appear in the ground state, (2) band structure that allows for long-range electron-hole exchange interaction, and (3) a finite magnetic field. When these conditions are fulfilled, superfluidity and ferroelectric order can coexist in two-dimensional excitonic insulators. Our results provide an example where coupling to the vacuum electromagnetic near field leads to a finite temperature second-order phase transition.

Laser-driven proton acceleration provides a powerful route for generating ultrashort, high-charge proton beams. Many applications, including secondary neutron sources and inertial fusion, benefit from tight proton beam focusing. Concave targets offer a robust solution, yet the scaling of proton focusing with laser and target parameters remains poorly understood. Here, we present a numerical study of laser-driven proton acceleration and focusing from hemispherical targets using the fully kinetic, relativistic Particle-In-Cell code EPOCH. We focus on the subpicosecond laser-pulse regime (duration $\lesssim {10}^2$ fs), centering on the laser parameters of our recent experiment at the Colorado State University ALEPH laser facility. We investigate the proton acceleration mechanisms, characterize proton focusing, and assess how focal spot parameters scale with laser and target parameters. We identify Target Normal Sheath Acceleration as the dominant mechanism, supplemented by a secondary postacceleration stage near the geometrical center of the hemisphere. We demonstrate that both the proton focal spot size and focal plane position scale approximately linearly with the hemisphere radius, with the focal plane consistently located downstream of the geometrical center. The opening angle of the concave target mainly affects the proton beam waist. Energy-dependent proton focusing can be understood, in part, as arising from the evolving curvature of the accelerating structure, which departs from the target curvature. Evidence for self-similar proton focusing is found in the regime of nearly uniform target irradiation.