A single quantum emitter coupled to a structured non-Hermitian environment shows anomalous bound states and real-time dynamics without Hermitian counterparts, as shown in Gong et al. [Phys. Rev. Lett. 129, 223601 (2022)]. In this work, we establish a general approach for studying the scattering states of a single quantum emitter coupled to one-dimensional non-Hermitian single-band baths. We formally solve the exact eigenvalue equation for all the scattering states defined on finite periodic lattices. In the thermodynamic limit, the formal solution reduces to the celebrated Lippmann-Schwinger equation for generic baths. In this case, we find that the scattering states are no longer linear superpositions of plane waves in general, unlike those in Hermitian systems; instead, the wave functions exhibit a large, yet finite localization length proportional to the lattice size. Furthermore, we show and discuss the cases where the Lippmann-Schwinger equation breaks down. We find the analytical solutions for the Hatano-Nelson and unidirectional next-to-nearest-neighbor baths in the thermodynamic limit.

Distributing entanglement among distant quantum nodes is essential for building scalable quantum networks. In this paper we propose a scheme to generate multipartite magnonic entanglement in a cavity optomagnonic network via measurement-based feedback. We consider $N$ spatially separated cavity optomagnonic systems and the cavity outputs are coupled through a beam-splitter array. The fields from the array's output ports are subjected to continuous homodyne detection, and the measurement outcomes are fed back to the systems. We analytically demonstrate that multipartite magnonic entanglement can be deterministically generated in the present scheme by tuning the local phases of homodyne detection appropriately. The multipartite entanglement arises from photon-magnon entanglement, which is distributed among the magnonic modes via the beam-splitter-array interferometric measurement. We further reveal that the multipartite entanglement is optimized when the cavity field couples to the magnonic mode via a two-mode squeezing interaction in each cavity optomagnonic system, because such an interaction induces optimal magnonic squeezing when homodyning the cavity output. The present scheme can be directly extended to other light-matter systems for realizing multipartite entanglement of continuous variables. Beyond advancing fundamental quantum research, this work provides a practical platform for magnon-based quantum technologies.

Recent foundational studies have established the bulk-edge correspondence for nonlinear eigenvalue problems using auxiliary eigenvalues $\widehat{H}\mathrm{\Psi }=\omega S\left(\omega \right)\mathrm{\Psi }$, spanning both linear [T. Isobe et al., Phys. Rev. Lett. 132, 126601 (2024)] and nonlinear [C. Bai and Z. Liang, Phys. Rev. A 111, 042201 (2025)] Hamiltionians. This progress prompts a fundamental question: Can eigenvalue nonlinearity generate observable physical phenomena absent in conventional approaches ($\widehat{H}\mathrm{\Psi }=E\mathrm{\Psi }$)? In this work, we address this question by demonstrating a uniquely nonlinear manifestation of the bulk-edge correspondence: fractional Thouless pumping of solitons. Through systematic investigation of nonlinear Thouless pumping in an extended Rice-Mele model incorporating next-nearest-neighbor (NNN) couplings, we uncover that NNN interaction parameters can induce fractional topological phases—even in the presence of quantized topological invariants as predicted by conventional linear approaches. Crucially, these fractional phases are naturally explained within the auxiliary eigenvalue framework, directly linking nonlinear spectral characteristics to the bulk-boundary correspondence. Our findings reveal emergent phenomena arising from the interplay between nonlinearity and NNN couplings, providing key insights for the design of topological insulators and the controlled manipulation of quantum edge states in nonlinear regimes.

In quantum information processing, the preparation and optimization of entanglement sources are critical steps. This paper explores reality-enhanced entanglement in two-mode squeezed vacuum states via three-photon quantum scissors (3-QS). Crucially, in realistic scenarios, the optimized 3-QS scheme achieves stronger entanglement than ideal scenarios while expanding the effective enhancement range. By adjusting beam-splitter transmittance in experimentally accessible weak squeezing regimes, we achieve enhanced entanglement and higher quantum teleportation fidelity compared to conventional strong squeezing approaches. This scheme provides a practical path toward long-distance quantum communication by transforming low-quality squeezed states into high-fidelity entanglement resources.

Characterizing the error sources of quantum devices is essential for building reliable large-scale quantum architectures and tailoring error correction codes to the noise profile of the devices. Tomography techniques can provide detailed information on the noise or quality of quantum states but are typically both computationally and experimentally intensive with respect to the system's size. For quantum error correction experiments, however, the information captured by a detector error model is sufficient for extracting the success rate of the experiment, as well as some information about the underlying noise. In this work, we estimate Pauli noise on detector error models, including hypergraphs, using only the syndrome statistics. We apply this method to well-known codes such as the repetition, surface, and two-dimensional color codes. Under bare-ancilla syndrome extraction, two-point correlations are enough to reconstruct the detector error model for repetition or surface codes. For color codes or repetition codes under Steane-style syndrome extraction, we show how to extend the estimation method to multipoint correlators and extract the error rates of the hypergraphs. Finally, we find an increase in logical error suppression when we calibrate the decoder to noise fluctuations typically present in experiments.

Network self-testing enables the unique identification of unknown measurements in a network using only observed measurement statistics. In this work, we first establish the self-testing statements for measurements in a three-branch star-shaped network (3BSN) scenario based on genuine network nonlocality. In this network, the central node performs a single joint measurement, while each branch node implements three binary-outcome projective measurements. We propose a set of statistical constraints for one pair of measurements (the first and second) at each branch node, and, by exploiting the maximal violation of the Mermin inequality for another pair (the second and third), we demonstrate the self-testing of the measurements in this 3BSN scenario. Subsequently, by performing a joint measurement on branch nodes from two discussed 3BSNs, we construct a three-layer two-forked tree-shaped network. We then establish the self-testing protocol of the joint measurement in this newly formed network scenario. In conjunction with the self-testing statements for each individual 3BSN scenario, this establishment enables the self-testing of all measurements in the tree-shaped network scenario. Our self-testing approach does not rely on any network Bell inequalities, thus providing a different perspective for device-independent quantum information processing tasks in networks.

In continuous-variable (CV) QKD with optical coherent detection, the widely adopted trusted detector noise model improves both the secret key rate and the transmission distance. This model assumes that detector noise is inherently random and inaccessible to an adversary. While substantial research has focused on shielding the detector, it is far more difficult to justify the adversary's ignorance of the detector noise. In this paper, we introduce a calibrated detector noise model for CV-QKD, which relies solely on the isolation of the detector from the adversary's intervention. Specifically, our model applies even when detector noise is predictable to the adversary. We analyze the electrical noise of a commercial balanced photoreceiver and perform numerical simulations to compare different noise models. Our results show that when the detector noise variance is an order of magnitude below the vacuum noise, the proposed model achieves a secret key rate comparable to that of the trusted detector noise model, while eliminating the questionable assumption of “truly random” detector noise.

Time-resolution protocol of quantum sensing aims to measure the fast temporal variation of an external field and demands a high field sensitivity in a short interrogation time $\tau$. Since any operation that evolves the quantum state takes time and is counted as part of the interrogation, evaluating the performance of the time-resolution protocol requires a complete end-to-end description of the measurement process. In particular, the initial state has to be one of the quantum sensor's eigenstates in the absence of external fields, and the final projective measurements must be performed in the same eigenstate basis. Building upon prior works which proposed limits for time-resolved sensing using a quantum sensor, we apply optimal control theory to optimize the time-resolution protocol. Our analysis indicates that there exists a critical interrogation time $T^{*}$: When $\tau <T^{*}$ the optimal protocol is a purely bang-bang strategy; when $\tau >T^{*}$ the optimal protocol involves a singular control during the interrogation. In the short-$\tau$ regime, which is relevant to high time resolution, we propose a detune protocol that involves only smooth control during the entire interrogation. As the discontinuities of control pose the main obstacles to experimental realization, we expect the presented detune protocol to be practically useful. In the long-$\tau$ regime, the optimal protocol closely resembles the Ramsey sequence; protocols based on maximizing quantum Fisher information are constructed to highlight the difference between the theoretically optimal and practically implementable measurements. Effective use of the time-resolution protocol requires a setup where the unknown time-domain signal of interest can be identically and repeatedly generated. As a potentially relevant application, we outline the calibration of baseband flux pulse distortion in the control of superconducting qubits.

We establish a simple quantitative relationship between the environmental memory effects and the characteristics in a dynamical decoupling process. In contrast to previous works, our measures of non-Markovianity are tailored and extended to evaluate the strength of memory effects in dynamical decoupling. We find that if each kick commutes with the dynamical map of the uncontrolled system, then the change of the final dynamical map or the final state brought by the control (called the “effect of control”) is upper (lower) bounded by the summation (difference) of the strengths of memory effects with and without control. We propose sufficient conditions for the commutation relation for parity kicks and illustrate our finding with a dissipative quantum Rabi model by numerical simulations where one or many cycles of parity kicks are implemented on the qubit. Besides, the results show that under certain conditions, the effect of control or the increase of performance by the control may be simply proportional to the strength of memory effects with or without control.

Long-range entanglement distribution in a quantum network relies on entanglement swapping at intermediate nodes along a network path to connect short-range entangled states established over the network edges. The end-to-end entanglement of a network path obtained via this process determines the utility of the network path for executing entanglement enabled tasks and for the design of entanglement routing protocols in the quantum network. Here we study the end-to-end entanglement of paths in a quantum network when the edges are characterized by multiparameter quantum states that may be considered to be the output of arbitrary and unknown quantum channels described by the network's edges. We find that over ensembles of multiparameter states with fixed concurrence but varying density matrix elements, the end-to-end entanglement takes a range of values upper bounded by a function of the concurrence of the network-edge states. The scaling behavior of the average end-to-end entanglement reveals that its distribution gets increasingly concentrated around the mean as the paths become longer. For a network path of a given length, the average end-to-end entanglement vanishes for edge concurrence values below a threshold that increases with the path length. Although, for edge concurrence values greater than the threshold the average end-to-end entanglement increases faster with the length of the path. As an implication of our results, we show that the optimal path for entanglement distribution between a pair of end nodes, connected by alternate paths with multiparameter states along the edges, can be indeterminate given only entanglement guarantees along the network edges.

We demonstrate that energy levels of excited states in a hydrogenic system consisting of an arbitrary nucleus and an antiproton can be calculated within the framework of nonrelativistic quantum electrodynamics, even for a large nuclear charge $Z$. It is because for rotational states the expansion parameter is $Z\alpha /n$. The main advantage of this approach is the possibility of exact inclusion of the finite nuclear mass, which we achieve up to the ${\left(Z\alpha \right)}^6$ order. In addition, we include unperturbatively the one-loop and two-loop electron vacuum polarization (EVP) potentials in the nonrelativistic Hamiltonian, as well as in the leading relativistic correction. The obtained results for $l>1$ states of antiprotonic atoms with a spinless nucleus are the most accurate to date. We make available a user-friendly mathematica code for antiprotonic atoms pbarspectr, which can be further improved by combining EVP potentials with ${\left(Z\alpha \right)}^5$ QED effects, by adding three-loop EVP, and by extending to an arbitrary nuclear spin. Finally, we note that rotational states of antiprotonic atoms can be used to determine the mean-square nuclear charge radius much more accurately than from electronic or muonic atoms.

We theoretically demonstrate the two-color-driven selective enhancement of high-order harmonic generations (HHGs) across a broad frequency range, spanning from the extreme ultraviolet (EUV) to the near-soft x-rays. The enhancement of harmonics, particularly at a central wavelength of ${\lambda }_{\text{H}118}=13.5\mathrm{nm}$, is of significant interest in the field of lithography. We identify two distinct enhancement mechanisms for HHGs in argon (Ar) and neon (Ne) gases: the enhancement of the 42nd harmonic (H42) in Ar is attributed to a coherent superposition of enhanced single-atom response harmonics in the off-axis region, whereas the enhancement of H118 in Ne is due to phase-matching selection of harmonics in the off-axis region. Through quantum orbit analysis, we demonstrate that phase matching is primarily influenced by the control of the amplitudes of the most relevant orbits in the off-axis region, which is associated with the modulation of the third strong peak of the driving field within the gaseous medium. This work presents a purely optical methodology for producing table-top tunable coherent sources of EUV or soft x-ray light.

One-dimensional Bose gases present an interesting setting to study the physics of Bose polarons, as density fluctuations play an enhanced role due to reduced dimensionality. Theoretical descriptions of this system have predominantly relied on contact pseudopotentials to model the impurity-bath interaction, leading to unphysical results in the strongly coupled limit. In this work, we analytically solve the Gross-Pitaevskii equation, using a square-well potential instead of a zero-range potential, for the ground-state wave function of a static impurity. We compute perturbative corrections arising from infinitesimally slow impurity motion. The polaron energy and effective mass remain finite in the strongly coupled regime, in contrast to the divergent behavior obtained using a contact potential. In this limit, we characterize the polaron properties in terms of the dimensionless ratio $\tilde{w}\equiv w/\xi$ between the interaction range $w$ of the impurity-bath potential and the coherence length $\xi$ of the Bose gas. The effective mass exhibits a $1/\tilde{w}$ scaling. The energy of the attractive polaron scales as $-1/{\tilde{w}}^3$, whereas the repulsive polaron features subleading corrections to the dark soliton energy at the order ${\tilde{w}}^3$.

We introduce a family of operators exploiting the symmetry of superpositions of quadrature eigenstates (SQEs) and demonstrate how the associated nonlinear squeezing, quantified by the expectation value of such operators, serves both as a witness of non-Gaussianity and as an indicator of the quality of SQE approximations. To establish the usefulness of this measure, we connect it to quantum state fidelity and evaluate its implications in breeding protocols. Finally, we construct optimal approximations of SQE states in truncated Fock spaces.

Sequential quantum information processing may lie in the peaceful coexistence of no-go theorems on quantum operations, such as the no-cloning theorem, the monogamy of correlations, and the no-signalling principle. In this work, we investigate a sequential scenario of quantum state discrimination with maximum confidence, called maximum-confidence discrimination, which generalizes other strategies such as minimum-error and unambiguous discrimination. We show that sequential discrimination with equally high confidence can be realized if and only if positive-operator-valued measure elements for a maximum-confidence measurement can be unambiguously discriminated, i.e., linearly independent; otherwise, a party will have strictly less confidence in measurement outcomes than the previous one. We investigate the tradeoff between state disturbance and information gain in sequential state discrimination and show that the less guessing probability there is from conclusive outcomes for each party, the more parties can participate in the sequential scenario.

In this paper, we focus on discrete-variable quantum systems of odd prime dimension. We investigate the quantum capacity of stabilizer convolution channels under a variety of environmental states. Inspired by the recent result of Bu and Jaffe [Phys. Rev. Lett. 134, 050202 (2025)], our main contribution is to generalize the analysis beyond the discrete beam splitter—which is only applicable for odd prime dimensions $d\ge 7$—to broader classes of stabilizer convolutions, allowing us to explore the behavior of magic resources in lower dimensions such as $d=3$ and $d=5$, where their role in enhancing quantum capacity has remained unclear. In fact, many of our mathematical results are derived under the broader setting of positive convolutions, not limited strictly to stabilizer convolutions.

Arrays of optically trapped neutral atoms are an emerging platform for scalable quantum computing, where achieving high-fidelity entangling gates remains a central challenge. We present a systematic analysis of the two-qubit controlled-Z (cz) gate under finite Rydberg blockade, paying particular attention to the influence of near-degenerate Rydberg pair states and resonant dipole-dipole interactions. Using the global two-pulse excitation protocol, we model the full gate dynamics, explicitly capturing population leakage into noncomputational states. By analyzing the interplay between the control parameters such as Rabi frequency, detuning, the Förster defect, and interaction strength, we identify conditions that enable fast, high-fidelity gate operation while minimizing leakage. We also quantify the impact of finite Rydberg-state lifetimes on gate error and further demonstrate that the optimal parameter regimes identified here are accessible in current rubidium-based tweezer experiments. These results provide practical guidance for optimizing two-qubit gate protocols in neutral-atom quantum processors with experimentally accessible conditions.