Area laws describe how entanglement entropy scales and thus provide important necessary conditions for efficient quantum many-body simulation, but they do not, by themselves, yield a direct measure of computational complexity. Here we introduce a complementary framework based on $p$-particle positivity conditions from reduced density matrix (RDM) theory. These conditions form a hierarchy of $N$-representability constraints for an RDM to correspond to a valid $N$-particle quantum system. We prove a general complexity bound: if a quantum system is solvable with level-$p$ positivity independent of its size, then its entanglement complexity scales polynomially with order $p$. We also show that locality provides one mechanism for satisfying this complexity bound, establishing connections to area laws. Positivity laws provide a rigorous framework for understanding entanglement complexity and certifying when many-body methods—including RDM approaches—can efficiently simulate correlated quantum matter and materials.

Starting from the interaction picture in quantum mechanics it is shown that perturbation theory for a weak static coupling of two subsystems in a natural way can be reformulated through integrals over products of imaginary time cross correlation functions. This inter alia leads to an expression for the London dispersion energy contribution of intermolecular interactions offering new ways to its numerical computation. The frequency-dependent charge susceptibility functions at imaginary frequencies appearing in the Casimir-Polder expression for the dispersion energy and the imaginary time density fluctuation cross correlation functions occuring in the equivalent alternative formula turn out to be Fourier cosine transform pairs.

Dipoles in triangular optical ladders constitute a flexible platform for the study of the interplay between geometric frustration and long-range anisotropic interactions, and in particular for the observation of the spontaneous onset of chirality. Frustration magnifies the effect of the dipolar interactions in itinerant polarized dipolar bosons. As a result, the dipole-induced transition between a chiral superfluid and a nonchiral two-component superfluid may be observed for current state-of-the-art temperatures even for the weak intersite interaction characterizing magnetic atoms in standard optical lattices. On the other hand, pinned spin-$1/2$ dipoles, which we discuss in the context of polar molecules in two rotational states, realize frustrated dipolar XXZ spin models. By controlling the external electric field strength and orientation, these systems can explore a rich ground-state landscape including chiral and nematic phases, as well as intriguing chiral dynamics.

We report a normal-mode induced synchronization blockade in coupled quantum van der Pol oscillators under the influence of external drive. In this mechanism, the coupling hybridizes the oscillator modes into spectrally split normal modes. The destructive interference between the transitions to these modes blocks synchronization. We find that this blockade can be controlled simply by tuning the coupling strength and detuning allowing dynamic manipulation of quantum synchronization through collective mode dynamics. We analyze the phase-locking behavior using perturbation analysis. Further, by deriving steady-state probability amplitudes we show how the energy redistribution and spectral splitting forms the basis of the blockade. Our results might provide new insights into how synchronization can be controlled in quantum systems.

We investigate the sensitivity of gravitational acceleration estimation using squeezed probe states in a quantum metrology framework. In particular, we analyze how the squeezing phase, beyond its amplitude, affects the attainable precision. We show that probes squeezed along the canonical phase-space quadratures can surpass the shot-noise limit only in specific time regimes, whereas position-momentum correlated input states can consistently overcome this limit across all interaction times. Furthermore, we demonstrate that optimal sensitivity can be achieved by combining projective momentum measurements with a time-dependent adjustment of the squeezing phase. Our results highlight the fundamental role of phase-engineered squeezing in quantum gravimetry protocols and provide new insights into the design of optimized sensing strategies.

We explore the effect of self-orthogonality at exceptional points (EPs) in non-Hermitian parity-time-symmetric systems. Using a driven three-band lattice model, we show that the Rabi frequency diverges as the system approaches an EP due to the coalescence of eigenstates. We demonstrate that this divergence manifests in experimentally accessible power oscillations, establishing a direct observable for self-orthogonality. Our results provide a pathway for probing EP physics in various metamaterial platforms.

We address the long-standing problem of determining accurate, time-resolved ionization rates for atoms in strong laser fields, a quantity that is fundamental to attosecond science. We show that it is possible to retrieve sub-optical-cycle dynamics of strong-field ionization from ionization probabilities obtained for a set of few-cycle laser pulses that covers a sufficiently broad parameter space. To this end, we introduce the general approximator for strong-field ionization rates, a retrieval tool that uses a few adjustable parameters to accurately reconstruct ab initio data. By imposing only essential physical constraints, our model provides a versatile framework for time-domain investigations of strong-field ionization and the role of ionization dynamics in attosecond metrology and lightwave electronics.

By employing singles, doubles, and triples excitations within the relativistic coupled-cluster framework, we perform comprehensive calculations of a wide range of atomic properties for the ${\mathrm{Th}}^{3+}$ ion. These properties are essential for advancing nuclear clock technology and probing fundamental physics. Combining our isotope shift parameters with experimental data, we estimate highly accurate values of the differential nuclear charge radii for ${}^{232,229}\mathrm{Th}$ and ${}^{229m,229}\mathrm{Th}$. Additionally, we determine the nuclear magnetic dipole and electric quadrupole moments for both the ground and isomeric states of ${}^{229}\mathrm{Th}$ by combining measured hyperfine-structure constants with our theoretical calculations. Our precise evaluations of electric dipole polarizabilities and hyperfine-induced quadrupole moments are critical for assessing systematic uncertainties in ${}^{229}\mathrm{Th}^{3+}$-based nuclear clocks. Notably, we observe unexpectedly significant contributions from higher-order relativistic effects and excitations involving orbitals with higher angular momentum, which markedly influence the energies of the ground state and its fine-structure partner. These results highlight the substantial challenges in achieving highly accurate predictions for these properties.

We present a closed-form analytic solution for the propagation of an arbitrary charged scalar state in a nonuniform magnetic field. The dynamics are governed by classical beam optics parameters (Courant-Snyder parameters), the Twiss functions, and phase advance, revealing a direct map between quantum evolution and its classical counterpart. The solution decomposes into three components, exhibiting a complex rotation dependent on the sign of the orbital angular momentum projection, alongside an intrinsic distortion from interference governed by a generalized Gouy phase. For a relevant Glaser-type magnetic field and a half-blocked twisted electron, we demonstrate that asymmetry reveals interference-driven dynamics beyond rigid rotation. Our fully relativistic framework provides a practical tool for predicting beam behavior in particle accelerators and electron microscopes.

Terahertz (THz) radiation is widely utilized for its classical electromagnetic properties, while its quantum aspects are typically overlooked. In this work, we propose a scheme to generate quantum THz waves by employing bright squeezed vacuum states in strong laser-gas interactions. This approach significantly enhances both the bandwidth and yield of the emitted THz radiation. The resulting bunched THz photons exhibit super-Poissonian statistics, and their Wigner function corresponds to a thermal-like mixed state. The quantum nature of the generated THz waves paves the way for novel applications in sensing, communication, and beyond.

We demonstrate that the future and left Rindler wedges of Minkowski spacetime are entangled, leading to the Unruh effect. Similarly, the past and right Rindler wedges are also entangled. We propose a protocol to extract this entanglement using two two-state detectors located in the past and right Rindler wedges. By scaling the detector transition frequencies inversely with Minkowski time, entanglement from the quantum field is transferred to the detectors, suggesting they may support quantum teleportation via the vacuum. Our protocol can be implemented with current quantum systems, such as flux-tunable transmon qubits. This research provides new insights into the entanglement properties of spacetime and hints at practical applications for secure quantum information transfer using the vacuum state of a quantum field.

A gas of ultracold atoms probed with laser light is a nearly ideal experimental realization of a medium of resonant pointlike scatterers, a key problem from condensed matter to biology or photonics. Yet, several recent experiments have reported large discrepancies with theory. In this Letter, we measure the complex transmission through a slab of ultracold two-level atoms with an interferometric technique. Our measurements are compatible with first-principles simulations of mutually coupled, laser-driven dipoles, and provide an explanation for the discrepancies in earlier measurements.

We derive analytical results for continuous-time quantum walks from a class of initial states with tunable delocalization. The dynamics are governed by a Hamiltonian with complex hopping amplitudes. We provide closed-form equations for key observables, revealing three notable findings: (1) the emergence of directed quantum transport from completely unbiased initial conditions; (2) a quantum backfire effect, where greater initial delocalization enhances short-time spreading but counterintuitively induces a comparatively smaller long-time spreading after a crossing time $t_{\mathrm{cross}}$; and (3) an exact characterization of survival probability, showing that the transition to an enhanced $t^{-3}$ decay is a fine-tuned effect. Our work establishes a comprehensive framework for controlling quantum transport through the interplay between intermediate initial delocalization and Hamiltonian phase.

We show how a Fujita-Miyazawa-type three-body force emerges among three impurity atoms immersed in an atomic Bose-Einstein condensate near an interspecies Feshbach resonance. As a result of the thermal average over excitations in the medium and impurities as well as expansion with respect to the impurity-medium and Feshbach resonance couplings, two superfluid phonons and a closed-channel resonance play a role in producing an effective three-body force, as in the original three-nucleon case in which two pions and a $\mathrm{\Delta }$ resonance are involved. The proposed Fujita-Miyazawa-type three-body force can be enhanced by tuning the closed-channel energy level via an external magnetic field, and moreover, its strength can be confirmed experimentally by measuring the impurity equation of state. Our result gives a new insight into the analogy between atomic polarons and nuclear few-body systems.

We demonstrate characteristics of a bosonic fractional quantum Hall (FQH) state in a one-dimensional extended Bose-Hubbard model (eBHM) with a static tilt. In the large tilt limit, quenched kinetic energy leads to emergent dipole moment conservation, enabling mapping to a model generating FQH states. Using exact diagonalization, density matrix renormalization group, and an analytical transfer matrix approach, we analyze energy and entanglement properties to reveal FQH correlations. Our findings set the stage for the use of quenched kinetics in simple time-reversal invariant eBHMs to explore emergent phenomena.

In the framework of open quantum systems, we derive the dynamical equation governing two-time correlation functions in the ultrastrong-coupling (USC) regime between the system and its environment. Unlike the case of the standard weak-coupling regime, in the USC case, we find distinct relaxation behavior for two-time correlators depending on the types of the operators involved in the correlation function. Interestingly, the quantum regression theorem emerges after the fastest relaxation time scale, which is governed by the system-bath coupling strength. We exemplify our findings for the dissipative spin-boson model and further find excellent agreement with the numerically exact hierarchical equations of motion method.

Quantum channels describe the most general dynamics of open quantum systems. A quantum channel, as a linear map on vectorized quantum states, can be represented by a single matrix, whose spectrum is called the channel spectrum. Here, we propose a general method to measure the channel spectrum and apply this method to Hamiltonian parameter estimation. We first demonstrate that the channel spectrum can be measured by tracking the probability of a specific outcome in repeated application of the same channel. Then, we construct and analyze a class of concatenated channels, with each one being a unitary channel on a target quantum system followed by a weak-measurement channel induced by a Ramsey measurement on a probe qubit. We show that the spectrum measurement of such concatenated channels can be utilized for estimating the parameters in the free Hamiltonians generating the unitary channels of the target system. As practical examples, we numerically demonstrate that a probe spin qubit can accurately sense nuclear spin clusters for nanoscale nuclear magnetic resonance.

High-accuracy calculations of electric dipole polarizabilities and quadrupole moments ($\mathrm{\Theta }$) of the clock states of the singly charged calcium (${\mathrm{Ca}}^{+}$), strontium (${\mathrm{Sr}}^{+}$), and barium (${\mathrm{Ba}}^{+}$) alkaline-earth ions are estimated by employing relativistic coupled-cluster (RCC) theory. It demonstrates the importance of the triple excitations in the RCC method for precise determination of the above quantities. We also observe a different trend of correlations in the $\mathrm{\Theta }$ values than an earlier study with respect to orbitals from higher angular momenta. Reliability of the results is verified by comparing the calculated energies, magnetic dipole hyperfine structure constants, and lifetimes of the atomic states with the experimental values of the ${}^{43}\mathrm{Ca}^{+}, {}^{87}\mathrm{Sr}^{+}$, and ${}^{137}\mathrm{Ba}^{+}$ ions. Nuclear quadrupole moments of these isotopes are also estimated by combining calculations with the measured electric quadrupole hyperfine structure constants, showing large deviations from the literature values.

Inspired by investigations of Dirac, Majorana, and Weyl fermions in the context of particle, condensed-matter, and atomic physics, we propose theoretical and experimental platforms to create and detect massless helical boson modes that we call Weyl bosons, the bosonic cousin of Weyl fermions. We show that these exotic excitations arise in one-dimensional interacting Fermi gases, when spin-orbit coupling and Rabi fields are present. We obtain the phase diagram of chemical potential versus Rabi fields for given spin-orbit coupling and interactions, showing regions where zero, one, or two types of Weyl bosons exist. We find that, when two types of Weyl bosons emerge, they must propagate with different velocities. Furthermore, we show that the disappearance of any Weyl boson species is described by a topological quantum phase transition of the Lifshitz type, where the velocity of the disappearing Weyl boson vanishes and the velocity of the surviving Weyl boson develops a cusp at the transition boundary. Lastly, to detect the existence of Weyl bosons, we propose measurements of the dynamical structure factor tensor (charge-charge, charge-spin, and spin-spin), where the energy dispersions, spectral weights, and helicities of the emergent Weyl bosons can be experimentally extracted in systems such as ${}^6\mathrm{Li}, {}^{40}\mathrm{K}$, and ${}^{173}\mathrm{Yb}$.

Bell's test, initially devised to distinguish quantum theory from local hidden-variable models through violations of local bounds, is also a common tool for detecting entanglement. For this purpose, one can assume the quantum description of devices and use available information to strengthen the bound for separable states, which may go beyond the local bound, enabling more efficient entanglement detection. Here we present a systematic approach for strengthening Bell inequalities for qubit systems, using Mermin-Klyshko-Bell inequalities as examples, by considering measurement devices that are coarsely calibrated only by their ability to generate nonlocal correlations without requiring precise quantum characterization. In the case of bipartite and tripartite systems, we derive trade-offs between upper bounds for separable states and general states in terms of structure functions to optimize the entanglement detection. We then strengthen $n$-partite Bell inequalities for the detection of states exhibiting a diversity of entanglement structures such as genuine multipartite entanglement. For general Bell scenarios with some measurements characterized, we demonstrate that entanglement can also be detected with some local correlations by exploiting the Navascués-Pironio-Acín hierarchy of tests.