We study the nonlocal advantage of quantum imaginarity (NAQI) and distillable imaginarity of assistance (DIA), which treat imaginarity as a resource in distributed scenarios. For two qubits interacting with a lossy cavity, it is shown that both the NAQI and DIA can be well preserved for long times in the presence of large and symmetric detuning between the qubits and the cavity. Moreover, the off-resonant interaction generates a high degree of NAQI and DIA from the initial product states of two qubits having the same detunings and unequal couplings to the cavity. Based on the effective coupling of the qubits induced by the cavity mode, we explain the physical mechanism underlying the validity of this strategy. Our findings shed light on the role that off-resonant interactions have in the efficient control of imaginarity in distributed scenarios.

We develop a unified framework to analyze $d$-dimensional quantum teleportation through the joint geometry of two complementary figures of merit: average fidelity $F$ (how well a protocol works on average) and fidelity deviation $D$ (how uniformly it works across the inputs). Technically, we formulate a representation-theoretical framework based on Schur-Weyl duality and permutation-symmetry calculus that reduces the higher-moment Haar averages to a finite set of trace invariants of the composed correction unitaries. This yields closed-form expressions for $F$ and $D$ in arbitrary Hilbert-space dimension and delivers tight bounds that link the admissible deviation directly to the gap from the optimal average performance. In particular, within the isotropic-noise model, any measured pair $(F,D)$ can be ported into a visibility estimate for isotropic-channel resources, turning the $(F,D)$ plane into a calibrated diagnostic map. We further cast the teleportation advantage and Collins–Gisin–Linden–Massar–Popescu (CGLMP) [Collins et al., Phys. Rev. Lett. 88, 040404 (2002)] inequality violation as two witness lines in the $(F,D)$ plane: one line certifies that $F$ beats the classical benchmark $2/(d+1)$, while the other line certifies the Bell nonlocality. Their identical slope but distinct intercepts expose a quantitative gap between “entangled yet local” and “genuinely nonlocal” resources.

Tensor network methods strike a middle ground between fully fledged quantum computing and classical computing by taking inspiration from quantum systems to significantly speed up certain classical operations. Their strength lies in their compressive power and the wide variety of efficient algorithms that operate within this compressed space. In this work, we focus on applying these methods to fundamental problems in image compression and processing and classical optics, such as wave-front propagation and optical image formation, by using directly or indirectly parallels with quantum mechanics and computation. These quantum-inspired methods are expected to yield faster algorithms, with applications ranging from astronomy and earth observation to microscopy and classical imaging more broadly.

We consider the estimation of a single unknown parameter embedded in a quantum state. Quantum Cramér-Rao bound (QCRB) is the ultimate limit of the mean squared error for any unbiased estimator. While it can be achieved asymptotically for a large number of quantum state copies, the measurement required often depends on the true value of the parameter of interest. Prior work addresses this paradox using a two-stage approach: in the first stage, a preliminary estimate is obtained by applying, on a vanishing fraction of quantum state copies, a suboptimal measurement that does not depend on the parameter of interest. In the second stage, the preliminary estimate is used to construct the QCRB-achieving measurement, which is then applied to the remaining quantum state copies. This is akin to two-step estimators for classical problems with nuisance parameters. Unfortunately, the original analysis imposes conditions that severely restrict the class of classical estimators applicable to quantum-measurement outcomes, hindering the application of this method. We relax these conditions to substantially broaden the class of usable estimators for single-parameter problems at the cost of slightly weakening the asymptotic properties of the two-stage method. We also account for nuisance parameters. We apply our results to obtain the asymptotics of quantum-enhanced transmittance sensing.

We study theoretically the collective excitations in a spin-1 $XY$ model with a quadratic Zeeman term and a long-range interaction that decays algebraically with the distance. Using the quantum-field theory based on the finite-temperature Green's function formalism, we analyze properties of the Nambu–Goldstone (NG) and Higgs modes in order to analytically evaluate the damping rate of the Higgs mode in the $XY$-ferromagnetic ordered phase near the quantum phase transition to the disordered phase. When the power of the algebraic decay is 3, as in the case of dipole-dipole interactions in Rydberg-atom systems, we show that in two dimensions the excitation energy of the Higgs mode exhibits a linear dispersion, whereas the dispersion of the NG mode becomes proportional to the square root of the momentum. We find that the damping of the Higgs mode is significantly suppressed by the long-range interaction. We also propose how to excite and probe the Higgs mode in Rydberg-atom experiments.

We propose a formulation of quantum measurement within a modified framework of frames, in which a quantum system—a single qubit—is directly coupled to a classical measurement bit. The qubit is represented as a positive probability distribution over two classical bits, $a$ and $a^{\prime }$, denoted by $p\left(a{a}^{\prime }\right)$. The measurement apparatus is described by a classical bit $\alpha =\pm 1$, initialized in the pure distribution $p\left(\alpha \right)=\frac{1}{2}(1+\alpha )$. The measurement interaction is modeled by a quasi-bistochastic process $S(b{b}^{\prime }\beta \mid a{a}^{\prime }\alpha )$—a bistochastic map that may include negative transition probabilities, while acting on an entirely positive state space. When this process acts on the joint initial state $p\left(a{a}^{\prime }\right)p\left(\alpha \right)$, it produces a collapsed state $p(b{b}^{\prime }\mid \beta )$, yielding the measurement outcome $\beta$ with the correct quantum-mechanical probability $p\left(\beta \right)$. We also show that the same framework extends consistently to two qubits, including local measurements on entangled states and a joint Bell-basis measurement. This approach bypasses the von Neumann chain of infinite couplings by treating the measurement register classically, while capturing the nonclassical nature of measurement through the quasi-bistochastic structure of the interaction.

For a given quantum state used in sensing, the quantum Cramér-Rao bound (QCRB) sets a fundamental limit on the precision achievable by an unbiased estimator of an unknown parameter, determined by the inverse of the quantum Fisher information (QFI). The QFI serves as an upper bound on the classical Fisher information (CFI), representing the maximum extractable information about the unknown parameter from measurements on a physical system. Thus, a central goal in quantum parameter estimation is to find a measurement, described by a positive operator-value measure (POVM), that saturates the QFI (achieves maximum CFI), and thereby achieves the QCRB. In the idealization that one uses pure states and unitary encodings for sensing, discontinuities can appear in the CFI but not the QFI. In this article, we demonstrate that these discontinuities are important features, quantifying how much Fisher information is lost in the presence of noise. We refer to this as the Fisher information “fragility.” We present a simple framework for understanding how discontinuities increase fragility through Jensen's inequality, and demonstrate how one can use this framework to design more robust POVMs for quantum advantage in metrology.

Low-energy (keV or less) antiprotons moving or scattering in ordinary matter is strongly affected by the interaction potential between the antiproton and the atoms. This interaction can be modeled by using potentials that have been obtained in quantum chemical calculations of the interaction between an antiproton and an atom with electron screening. To determine the interactions of antiprotons with any element, we here develop a universal antiproton-atom interaction potential. The potential is constructed by fitting a universal functional form to 14 pair-specific antiproton-atom potentials calculated with quantum chemical approaches and tested against three pair-specific potentials that were not part of the fit. We also report pair-specific screened antiproton-atom potentials for 17 elements, five of which are constructed in this work. By performing molecular dynamics simulations of the antiproton transmission through thin films, we show that the universal potential yields almost as good agreement with experiments as simulations carried out with the pair-specific potentials.

It is well established that electronic conical intersections (CIs) in molecular systems can be induced by laser light, even in diatomic molecules. The emergence of these light-induced degeneracies leads to strong coupling among electronic, vibrational, and photonic modes, which significantly influences ultrafast nuclear dynamics. In this work, we perform pump-probe numerical simulations on the NaH molecule, considering the first three singlet electronic states $[X^1{\mathrm{\Sigma }}^{+}\left(X\right),A^1{\mathrm{\Sigma }}^{+}\left(A\right), \text{and} B^1\mathrm{\Pi }\left(B\right)]$ and including several light-induced degeneracies in the theoretical model. To elucidate the ultrafast molecular dynamics, we study the combined effects of multiple light-induced nonadiabatic couplings and rotational motion of the nuclei together with the situation when the electronic angular momentum projected onto the diatomic axis couples with the angular momentum of the nuclei. We then calculate key dynamical observables such as dissociation probabilities, kinetic energy release (KER) spectra, and angular distributions of the photofragments within and above the linear regime. The discrepancies between the different employed models are relatively minor for the dissociation probabilities and KER spectra. In contrast, for angular distributions, the inclusion of electronic spin and orbital angular momentum leads to substantial differences between the three applied schemes in the small ejection angle region.

Time crystals (TC) can spontaneously break time translational symmetry, which have been studied and recently observed in different experimental platforms. The microwave dressing technique can be used to manipulate and enhance Rydberg-Rydberg interactions in an atomic ensemble, which provides a control knob for manipulating the system's dynamics. Here, we report the observation of a time-crystalline phase in a thermal Rydberg gas based on microwave dressing. The emergence and evolution of TC can be manipulated by many experimental parameters such as the power and the detuning of the microwave and the frequency detuning of optical fields. This research provides a platform for engineering interatomic interactions and investigating nonlinear dynamics, which has potential applications for quantum precision measurement and quantum simulation.

We report a two-color magneto-optical trap that continuously operates on the $\left(5s^2\right){}^{1}S_0\text{−}\left(5s5p\right){}^{1}P_1$ and $\left(5s5p\right){}^{3}P_2\text{−}\left(5s5d\right){}^{3}D_3$ transitions in ${}^{88}\mathrm{Sr}$. Owing to the sub-Doppler cooling from the metastable $\left(5s5p\right){}^{3}P_2$ state, a bimodal momentum distribution is observed, with the cold part of the ensemble reaching a temperature of $105\mu \text{K}$. A detailed simulation is established to explain the data. The absolute frequency of the $\left(5s5p\right){}^{3}P_2\text{−}\left(5s5d\right){}^{3}D_3$ transition is measured to be $603976473\pm 2\mathrm{MHz}$ using a frequency comb, improving the literature value. The accompanying magnetic trap is characterized, and is shown to contribute to the sequential production of ensembles with temperatures down to $45\mu \text{K}$.

We study ring dark solitons in a uniform two-dimensional strongly interacting Fermi superfluid with spin-orbital-angular-momentum coupling and reveal an unconventional realization of ring dark solitons characterized by localized spin polarization. We show that a ring dark soliton can acquire a pronounced spin polarization localized at its core, forming a magnetic ring dark soliton with a clear and intuitive physical origin. Unlike conventional dark solitons, whose hallmark is a strong density depletion accompanied by a $\pi$ phase jump, the magnetic ring dark soliton is primarily characterized by a localized spin-density texture while the total particle density remains nearly uniform. This makes the soliton difficult to detect through density measurements alone, but renders its magnetic signature particularly robust and experimentally accessible via spin-resolved imaging. Furthermore, we demonstrate that the spatial structure of the spin-orbital-angular-momentum coupling generates an effective energy minimum for the soliton, at which the magnetic ring soliton resides at a finite radius. This provides a simple and controllable mechanism for pinning and manipulating magnetic solitons in spin-orbital-angular-momentum coupled Fermi superfluids, highlighting their potential as a platform for studying magnetic and topological soliton excitations.

This paper makes analytic predictions for systems of strongly coupled fermionic gases above the critical temperature by exploiting the spacetime symmetry constraints. It is known that when the coupling reaches the unitarity limit, where the scattering length diverges, such systems behave as non-Fermi liquids, the mysterious state of matter that is thought to be a precursor for atypical quantum effects such as high-$T_c$ superconductivity. In this paper we will be studying such systems approaching unitarity, but still at strong coupling, and, using anomaly matching, will make first-principles predictions for the compressibility and magnetic susceptibility in terms of the scattering length $a$, the atomic mass $m$, and $\tilde{C}\left(a\right)$, the dimensionless contact parameter. Comparing our predictions to simulations, agreement is found to be within the theoretical errors. We explain how experimental verification of our predictions would be evidence of the existence of a gapped dilaton in the spectrum.

Quantum squeezing and sub-Poissonian statistics, as independent effects of different orders, reflect nonclassicality through reduced quantum noise of the quadrature components and narrowed number distribution, respectively. In some scenarios, however, these two effects are mutually exclusive. Recent advancements in the realm of the chip-embedded waveguide quantum electrodynamics enable experimental achievements of the giant spin ensemble (GSE) and the giant atom (GA) by coupling a millimeter-sized ferromagnetic yttrium-iron-garnet (YIG) sphere and a transmon-type superconducting qubit to the meandering waveguide at two well-separated points. Here, we propose a win-win scheme to simultaneously generate the optimal quadrature squeezing and the pronounced sub-Poissonian magnon-number statistics with high brightness, owing to the non-Hermitian anharmonicity of the energy levels based on the dissipative coupling within the GSE-GA waveguide system. Besides, the presence of the individual decay rates relaxes the range of the weak-driving condition, which is conducive to improving the brightness and the amount of the magnon squeezing. Physically, we find a direct correlation between the two-level-GA coherence (closely related to the single-magnon excitation processes) and the magnon squeezing (corresponding to spin noise reduction below the vacuum level) as well as the sub-Poissonian magnon-number statistics (corresponding to antibunching). More importantly, our approach is not only robust against the external damping rates and the driving detunings, but also requires neither complex design nor pump modulation, thus facilitating the practical implementation. With realistic experimental parameters, the analytical calculations match very well with the numerical simulations. This study provides insights for engineering versatile nonclassical magnon sources at microwave wavelengths through macroscopic YIG spin systems, integrating two key properties that hold potential to underpin the complex tasks in precision metrology and quantum communication.

We study helicity correlations of electron-positron pairs created by a homogeneous time-dependent electric field in the Sauter-Schwinger scenario. Our analysis is based on solving the Dirac equation with Feynman or anti-Feynman boundary conditions, which is equivalent to the scattering matrix approach widely used in high-energy physics. Most importantly, both these methods allow us to fully account for the helicity (or, more generally, spin) correlations of created particles. The influence of helicity correlations and the carrier-envelope phase of the electric pulse on the properties of topological structures (such as spirals and vortices) in momentum distributions of created particles is investigated. The generation of maximally entangled helicity states is discussed and the possibility of using a short electric pulse as a fast switch between them is indicated.