We consider a mobile impurity coupled to an ideal Fermi gas in one spatial dimension through an attractive contact interaction. We calculate the quasiparticle residue $Z$ exactly, based on Bethe Ansatz and diagrammatic Monte Carlo methods, and with a varational Ansatz up to one particle-hole excitation of the Fermi sea. We find that the exact quasiparticle residue vanishes in the thermodynamic limit as a power law in the number of particles, consistent with the Luttinger-liquid paradigm and the breakdown of Fermi-liquid theory. The variational Ansatz, however, predicts a finite value of $Z$, even in the thermodynamic limit. We also study how the presence of the impurity affects the density of the spin-up sea by calculating the pair correlation function. Subtracting the homogeneous background and integrating over all distances gives the charge $Q$. This charge turns out to grow continuously from 0 at zero coupling to 1 in the strong-coupling limit. The varational Ansatz predicts $Q=0$ at all couplings. So, although the variational Ansatz has been shown to be remarkably accurate for the energy and the effective mass, it fails even qualitatively when predicting $Z$ and the pair correlation function in the thermodynamic limit.

The electric-field distributions and space-time singularity curves are computed for ultrashort pulsed Laguerre-Gaussian laser beams having spatial chirp. Due to the breaking of cylindrical symmetry by the spatial chirp, the singularities trace complicated curves in space-time, which also vary for different combinations of radial and vortical orders. Analytical solutions are mostly presented along with a recipe for numerically calculating higher orders. The behavior of the singularities upon propagation is also shown, along with a discussion of the extension toward few-cycle pulses. These results are an example of how a simple physical scenario can result in highly complicated singular behavior in space-time.

We extend the celebrated Keldysh approach to obtain closed analytical expressions for the ionization rate in strong optical fields to the case of the driving field, containing the fundamental frequency and its second harmonic, which are orthogonaly polarized to each other. In this situation, the separation of the tunnel and multiphoton regions is governed by two Keldysh parameters. Interference of the inter-frequency cross-terms contributing to the ionizationm is discussed. Whereas in the multiphoton regime the ratio of intensities of the fundamental and second harmonics plays an important role, in the tunneling limit, the ionization rate becomes nearly independent of this ratio and therefore of the driving wave shape.

Multipartite non-Gaussian entanglement serves as a key physical resource for realizing universal continuous-variable quantum computation. Recently, three-mode spontaneous parametric down-conversion (SPDC), which enables the deterministic generation of non-Gaussian Greenberger-Horne-Zeilinger (GHZ) states, was observed in superconducting circuits, and the non-Gaussian entanglement properties of these states were characterized. However, to date, no criterion capable of detecting genuine $N$-partite non-Gaussian entanglement has been proposed. In this work, we put forward a set of necessary and sufficient conditions for the separability of $N$-mode non-Gaussian GHZ states generated by $N$-mode SPDC. Building on these separability conditions, we further derive a set of genuine $N$-partite non-Gaussian entanglement criteria. Through numerical modeling, we demonstrate that quantum states generated by four-mode SPDC exhibit full inseparability and genuine quadripartite non-Gaussian entanglement. Our results hold significant applications for the characterization and certification of multipartite non-Gaussian entanglement.

Multipartite quantum systems are subject to monogamy relations that impose fundamental constraints on the distribution of quantum correlations between subsystems. These constraints can be studied quantitatively through sector lengths, defined as the average value of $m$-body correlations, which have applications in quantum information theory and coding theory. In this work, we derive a set of monogamy inequalities that complement the shadow inequalities, enabling a complete characterization of the numerical range of sector lengths for systems with $N⩽5$ qubits in a pure state. This range forms a convex polytope, facilitating the efficient extremization of key physical quantities, such as the linear entropy of entanglement and the quantum shadow enumerators, by a simple evaluation at the polytope vertices. For larger systems ($N⩾6$), we highlight a significant increase in complexity that neither our inequalities nor the shadow inequalities can fully capture.

Nonstabilizerness (colloquially “magic”) characterizes genuinely quantum (beyond-Clifford) operations necessary for preparation of quantum states and can be measured by stabilizer Rényi entropy (SRE). For permutationally symmetric states, we show that the SRE depends, for sufficiently large systems, only on a constant number of expectation values of collective spin operators. This compact description is leveraged for analysis of spin-squeezing protocols, which inherently generate nonstabilizerness. Under one-axis twisting (OAT), the generation of optimal squeezing is accompanied by a logarithmic divergence of SRE with system size. Continued time evolution under OAT produces metrologically useful so-called kitten states, that is, superpositions of rotated Greenberger-Horne-Zeilinger states, that feature many-body Bell correlations but exhibit a smaller, system-size-independent SRE that decreases with increasing Bell-correlation strength. Our results reveal connections between nonstabilizerness, multipartite correlations, and quantum metrology and provide a practical route to quantify nonstabilizerness in experiments for precision sensing.

A particularly useful tool for characterizing multiqubit systems is the correlation tensor, providing an experimentally friendly and theoretically concise representation of quantum states. In this work, we analyze the evolution of the correlation tensor elements of quantum systems composed of $\frac{1}{2}$-spins, generated by mutual interactions and the influence of the external field. We focus on two-body interactions in the form of anisotropic Heisenberg as well as antisymmetric exchange interaction models. The evolution of the system is visualized in the form of a trajectory in a suitable correlation space, which, depending on the system's frequencies, exhibits periodic or quasiperiodic behavior. In the case of two $\frac{1}{2}$-spins we study the stationary correlations for several classes of Hamiltonians, which allows a full characterization of the families of density matrices invariant under the evolution generated by the Hamiltonians. We discuss some common properties shared by the two- and three-qubit systems and show how a strong external field can play a stabilizing factor with respect to certain correlation characteristics.

In this paper, we propose a method to probe entanglement in a theoretically inaccessible quantum system with either a discrete or continuous basis. Our approach leverages insights into the entanglement distribution within a four-partite quantum system, comprising two qubit-oscillator subsystems with dephasing interactions between each qubit-oscillator pair. The method involves measurements applied only to the accessible two-qubit subsystem, enabling a qualitative detection and characterization of quantum correlations in the inaccessible two-oscillator subsystem. This approach provides a framework for probing entanglement in continuous-basis systems where traditional measures are often inapplicable due to their complexity. Our findings also reveal an intriguing conservative flowlike behavior in the redistribution of entanglement among subsystems, suggesting that entanglement may exhibit conservative properties in pure composite quantum systems.

Quantum networks with independent sources allow observing quantum nonlocality or steering with just a single measurement per node of the network or without any inputs. Inspired by the recently introduced notion of swap steering, we consider here the triangle network scenario without inputs, where one of the parties is trusted to perform a well-calibrated measurement. In this scenario, we first propose a linear witness to detect triangle network swap steering. Then, by using the correlations that achieve the maximum value of this inequality and assuming that all the sources are the same, we can self-test the state generated by the sources and the measurements of the untrusted party. We then extend this framework to ring networks with an arbitrary number of nodes, with one of them being trusted. Interestingly, this is an example of a topologically robust quantum advantage, that is, one can observe steerability without assuming the network structure of the network, as well as noise-robust quantum advantage in a network. Additionally, by allowing the trusted party to perform tomography of their subsystems, we demonstrate that every bipartite entangled state will result in swap-steerable correlations in the ring network. For this purpose, we construct linear witnesses to detect ring network swap steering corresponding to every bipartite entangled state.

It has been shown that shared entanglement between two telescope sites can, in principle, be used to localize a point source by mimicking the standard phase-scanning interferometer, but without physically bringing the light from the distant telescopes together. In this paper, we show that a receiver that employs spatial-mode sorting at each telescope site, combined with preshared entanglement and local quantum operations, can be used to mimic the most general multimode interferometer acting on light collected from the telescopes. As an example application to a quantitative passive-imaging problem, we show that the quantum-limited precision of estimating the angular separation between two stars can be attained by an instantiation of the aforesaid entanglement-based receiver. We discuss how this entanglement-assisted strategy can be used to achieve the quantum-limited precision of any complex quantitative imaging task involving any number of telescopes. We provide a blueprint of this general receiver that involves quantum transduction of starlight into quantum memory banks and spatial mode sorters deployed at each telescope site, and measurements that include optical detection as well as qubit gates and measurements on the quantum memories. We discuss the relative Fisher-information contributions of local mode sorting at telescope sites vis-à-vis distributed entanglement-assisted interferometry, to the overall quantum-limited information about the scene, based on the ratio of the baseline distance to the individual telescope diameter.

We present a cavity-QED theory for generating squeezed light from semiconductor quantum dots (QDs) integrated in microcavities. We formulate equations of motion for an inhomogeneously broadened QD ensemble that is incoherently pumped and simultaneously driven by a coherent seed field, solve for steady states, and compute the output-field quadrature variances. The analysis identifies operating conditions that yield amplitude-quadrature squeezing, with photon-number fluctuations reduced below the coherent-state limit and squeezing levels as large as 5 dB attainable with presently accessible QD and cavity parameters using only $\sim 1 \mu \mathrm{W}$ pump power. We further show that quantum correlations originating from four-wave mixing play a dual role: they both shape the gain spectrum and generate squeezing. These correlations constitute the quantum counterpart of the mean-field (semiclassical) mechanisms responsible for self-mode locking in QD lasers and the ultranarrow lasing linewidths achieved under self-injection locking.

We investigate the long-time dynamics of the sine-Gordon (SG) model under a class of perturbations whose quantum field theoretic analog—via bosonization—corresponds to the massive Schwinger model describing $1+1$ dimensions relativistic quantum electrodynamics of Dirac fermions. Classical SG solutions offer critical insight into nonperturbative effects in this quantum theory, but capturing their long-time behavior poses significant numerical challenges. To address this, we extend a coarse-graining method to space-time using a dual-mesh construction based on the Minkowski metric. We first validate the approach against the well-studied variant of the SG model describing magnetic fluxon dynamics in Josephson transmission lines (JTLs), where analytical and numerical benchmarks exist. We then apply the method to the Schwinger-inspired SG model and uncover long-lived bound states—“Schwinger atoms”—in which a soliton is trapped by a fixed central charge. In certain regimes, the system exhibits limit cycles that give rise to positronium-like states of oppositely charged solitons, while in others such formation is suppressed. Accessing such long-time solutions requires a rigorous implementation of outgoing boundary conditions on a finite computational domain that provide radiative dissipation to allow relaxation toward states that exist only in an infinite domain. Here we provide such a construction. Our results also suggest the possibility of analog quantum simulation of relativistic quantum field theories with JTLs. These results demonstrate the utility of spatiotemporal coarse-graining methodology for probing nonperturbative structure formation in nonlinear field theories.

We investigate the kinetic uncertainty relation (KUR)—a fundamental trade-off between dynamical activity and current fluctuations—in two configurations of a maser heat engine. We find that KUR violations arise only in one model. This asymmetry originates from spontaneous emission, which breaks the structural symmetry between the configurations and modifies their coherence dynamics. While we analyze several contributing factors, including statistical signatures such as the Fano factor and the ratio of dynamical activity to current, our results show that the decisive mechanism is the slower decoherence in one configuration, which enables quantum violations of the classical steady-state KUR bound. By contrast, the faster coherence decay in the other configuration suppresses such violations, driving it closer to classical behavior. These findings highlight the critical role of decoherence mechanisms in determining fundamental thermodynamic bounds and provide insights for the design of quantum heat engines in which the control of decoherence is central to suppressing fluctuations and enhancing reliable performance.

Quantum coherence and entanglement are fundamental resources in quantum technologies, yet their efficient estimation for unknown states by employing minimal resources in experimental settings remains challenging, particularly in high-dimensional systems. We present a machine learning approach based on support vector regression (SVR) that directly estimates the coherence measures and the geometric measure of quantum entanglement using minimal experimental resources. Our method requires only the diagonal entries of the density matrix, along with the traces of the squared and cubed density matrices for quantum coherence, and additionally along with the traces of the squared and cubed reduced density matrix for estimating quantum entanglement. These quantities can be obtained through random measurements or a hybrid quantum-classical framework. This approach significantly reduces the resource overhead compared to quantum state tomography while maintaining high accuracy. Furthermore, the support vector quantile regression (SVQR) with pinball loss is employed to prevent SVR overestimation. This model not only ensures that over 95% of predictions are conservative lower bounds in most cases, but also maintains this lower-bound reliability for over 93% of predictions, despite 2% perturbations in the input features. The proposed technique provides a practical and scalable tool for characterizing quantum resources across computation, communication, and metrology applications.

We present an algorithm for performing quantum process tomography on an unknown $n$-qubit unitary $C$ from the Clifford group. Our algorithm uses Bell basis measurements to deterministically learn $C$ with $4n+3$ queries, which is the asymptotically optimal query complexity. In contrast to previous algorithms that required access to $C^{†}$ to achieve optimal query complexity, our algorithm achieves the same performance without querying $C^{†}$. Additionally, we show the algorithm is robust to perturbations and can efficiently learn the closest Clifford to an unknown non-Clifford unitary $U$ using query overhead that is logarithmic in the number of qubits.

The capability to detect multifrequency microwave electric fields is pivotal for advancing Rydberg-atom-based microwave sensing in radar and communication applications. However, this technology has been limited to high-sensitivity measurements at a single-frequency field, and the precise detection of dual-frequency fields remains a challenge. Here we investigate precise measurement of dual-frequency microwave electric fields under resonant and off-resonant conditions. Through experimental measurement and theoretical simulation, we identify distinctive features in the transmission spectrum and reveal the quantum mechanisms. Furthermore, the quantitative relationships between the transmission peak separations $\mathrm{\Delta }{f}_1, \mathrm{\Delta }{f}_2$, and $\mathrm{\Delta }{f}_3$ and the dual-microwave-field parameters are established and validated experimentally, leading to the measurement of the dual-frequency electric-field strengths. This work reveals quantum coherence dynamics in dual-microwave-dressed systems, paving the way for integrating deep learning to achieve high-precision parameter extraction and for investigating more complex multifrequency fields with a scalable approach.

We explore the existence and dynamical generation of rogue waves (RWs) within a one-dimensional quantum droplet-bearing environment. RWs are computed by deploying a space-time fixed point scheme to the relevant extended Gross-Pitaevskii equation (eGPE). Parametric regions where the ensuing RWs are different from their counterparts in the nonlinear Schrödinger equation are identified. To corroborate the controllable generation—relevant to ultracold atom experiments—of these rogue patterns, we exploit two different protocols. The first is based on interfering dam break flows emanating from Riemann initial conditions, and the second refers to the gradient catastrophe of a spatially localized waveform. A multitude of possible RWs are found in this system, spanning waveforms reminiscent of the Peregrine soliton, its spatially periodic variants—namely, the Akhmediev breathers—and other higher-order RW solutions of the nonlinear Schrödinger equation. Key elements of the shape of the corresponding eGPE RWs traced back to nonintegrability and the presence of competing interactions are discussed. Our results set the stage for probing a multitude of unexplored rogue-like waveforms in such mixtures with competing interactions and should be accessible to current ultracold atom experiments.

Phase-gradient metasurfaces (PGMs) have gained significant attention due to their exceptional ability to control light propagation. However, previous studies primarily focused on the diffraction characteristics of propagating waves, while the diffraction behavior of evanescent waves in PGMs remains largely unexplored. In this work, we systematically explore the interaction of the evanescent wave with PGMs, unveiling the diffraction rule and underlying mechanism. We demonstrate that integer parity plays a crucial role in the diffraction of evanescent waves with large wave vectors. Moreover, the parity-reversed diffraction rules exhibit a unique periodic nature of the PGM response within momentum space, leading to the emergence of a momentum zone with a width of $K=m\xi$ (where $m$ is the number of unit cells over supercell and $\xi$ is phase gradient). Notably, the diffraction behavior remains invariant when the incident wave vector is shifted by integer multiples of $K$. The periodic diffraction rules establish a theoretical framework for manipulating evanescent waves, enabling the perfect conversion of an arbitrary evanescent wave into a propagating wave in free space. This study provides a theoretical foundation for extracting evanescent wave information and designing far-field superresolution devices.