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.

The van der Waals transition metal dichalcogenide ${\mathrm{NiTe}}_2$ is investigated through soft x-ray photoelectron and absorption spectroscopy combined with density functional plus dynamical mean-field theory. We derive an electronic configuration of $d^9$ for the Ni ions with some admixture of $d^8$ and $d^{10}$, yielding an average $3d$ occupation of about 8.9. Despite the $d$ shell being open with non-negligible hole concentrations, calculations reveal the absence of local moments, thereby explaining the Pauli paramagnetic behavior as observed in magnetic susceptibility measurements. This behavior is unusual, particularly given that many Ni-based compounds exhibit strong electron correlations. We ascribe the silencing of correlation effects in this material to the fact that without the Ni–Te hybridization, the Ni would have the nonmagnetic full $d^{10}$ configuration, and that the Ni bands that get partially unfilled due to hybridization are extremely broad, making the holes “bandlike” or “highly delocalized”. The large Hubbard $U$ interaction does not become operative in this material.

Elastic electron scattering is one of the primary means of investigating materials on the atomic scale. It is usually described in a one-particle approach (the probe electron's evolution in a perturbative static potential), whereas we are dealing here with a two-body interaction between the probe and the sample, both described by separate quantum states, inducing entanglement. In this work, we present a quantum treatment of elastic electron scattering. We find that the entanglement between probe and scatterer can have far-reaching consequences, particularly on coherence and image contrast. As a timely example, we discuss decoherence in Bragg scattering on nanoparticles. We find that conventional scattering theory is recovered in most cases. The situation changes dramatically for freely evolving nanoparticles as, e.g., levitated motional ground states, an active field of research.

We rigorously analyze the nonequilibrium thermodynamic behavior of various formulations of quantum Brownian motion using the framework of stochastic thermodynamics. While the widely used Caldeira-Leggett master equation exhibits desirable thermodynamic features—such as the fulfillment of a detailed balance—it fails to ensure complete positivity. In contrast, several completely positive and trace-preserving extensions turn out to be thermodynamically controversial. We show that such extensions introduce anomalous phase-space structures that violate detailed balance at the steady state, leading to nonvanishing entropy production and spurious nonequilibrium currents lacking a clear physical interpretation. Our results highlight a fundamental tension between quantum consistency and thermodynamic equilibration in open quantum systems.

Photon entanglement is a fundamental resource for quantum technologies, yet it is extremely fragile especially in large quantum circuitry, which is necessary for quantum information processing and computing. We propose an integrated scheme for direct topological protection of entanglement, enabling robust transport of entangled photonic states, even when the photon dynamically evolves during propagation. Our platform relies on a two-dimensional discrete-time quantum walks in synthetic dimensions, supporting topological edge states at the interface between distinct domains. Thus far, in all previous approaches for exploiting topology to protect entanglement, the protection was linked to the position of the photon in the actual structure. In contrast, our scheme relies on a synthetic temporal dimension (time bins) where the entangled state is always reproduced, despite fluctuations or variations that may emerge in the system. Thus, our scheme provides precise temporal control important for synchronization and timing in quantum computation. By suppressing phase-sensitive errors—the most critical noise source in photonic platforms—our approach can lower the physical error rate below fault-tolerance thresholds and reduce the overhead typically required for scalable quantum information processing. The robustness to errors arises from the fact that the entangled state is preserved through correlations in the synthetic (temporal) dimension. As a result, we ensure that at specific designated times, the emergent state faithfully reproduces the initial entangled state, despite the photon having taken any dynamically evolving paths. This approach establishes a robust framework for directly protecting entanglement.