We report the dynamics of a single-mode squeezed vacuum in evanescently coupled waveguide arrays incorporating next-nearest-neighbor coupling (NNNC) and disorder. Using an extended tight-binding framework, we show that NNNC reshapes the system's dispersion (phase), breaks spectral symmetry, and introduces alternative quantum pathways for the evolution of quadrature squeezing. This leads to a squeezing revival, squeezing transfer, squeezed quadrature swapping within a mode $(Q\leftrightarrow P)$, and partial confinement of quantum noise near the excitation site in a larger waveguide array. Both on-site disorder (OSD) and hopping disorder (HoD) degrade local squeezing, localizing quantum noise to a few modes, where moderate NNNC enhances this confinement and stronger NNNC counteracts it in larger waveguide lattices. An analytical and numerical analysis of the model suggests that NNNC partially preserves local mode squeezing by providing alternative quantum routes for quadrature rotation, even in the presence of disorder. These results suggest a mechanism for engineering quantum-noise transport in integrated photonic lattices, where disorder and next-nearest coupling make the model more realistic for on-chip quantum technologies.

Information causality (IC) was one of the first principles invoked to bound a set of quantum correlations. For some families of correlations, this principle recovers exactly the boundary of the quantum set; for others, there is still a gap. We close some of these gaps using a quantifier for IC based on the notion of redundant information. This progress was made possible by the recognition that the principle of IC can be captured without referring to the success criterion of random access codes. We give strong numerical evidence that this definition is still obeyed by quantum correlations in the same scenario.

High-fidelity entangling gates in trapped-ion processors are most commonly realized by spectrally isolating a single motional bus mode. As the ion chain grows, however, the coupling of each ion to any one mode weakens, making single-mode gates progressively slower. Existing multimode schemes offer a partial remedy but rely on perturbative driving and rotating-wave approximations, imposing trade-offs between speed and fidelity that become more severe with chain length. We introduce a nonperturbative magnetic-gradient scheme in which all axial motional modes participate collectively in mediating the entangling interaction. Exact spin-motion decoupling is enforced at the end of the protocol by construction, so that the achievable gate speed is limited only by the available gradient strength and control bandwidth. The framework supports both multiqubit gates and selective two-qubit gates between arbitrary pairs in a linear string, including simultaneous operation on multiple pairs, and remains effective as the ion number increases.

Lindbladian quantum master equations (LEs) are the most popular descriptions for quantum systems weakly coupled to baths. But, recent works have established that in many situations, such Markovian descriptions are fundamentally limited: they cannot simultaneously capture populations and coherences even to leading order in system-bath couplings. This can cause a violation of fundamental properties like thermalization and continuity equations associated with local conservation laws, even when such properties are expected in the actual setting. This begs the question: given a physical situation, how do we know if there exists an LE that describes it to a desired accuracy? Here we show that, for both equilibrium and nonequilibrium steady states, this question can be succinctly formulated as a semidefinite program (SDP), a convex optimization technique. If a solution to the SDP can be found to a desired accuracy, then an LE description is possible for the chosen setting. If not, no LE description is fundamentally attainable, showing that a consistent Markovian treatment is impossible even at weak system-bath coupling for that particular setting. Considering a few qubit isotropic XXZ-type models coupled to multiple baths, we find that in most parameter regimes, LE description giving accurate populations and coherences to leading order is unattainable, leading to rigorous no-go results. However, in some cases, the LE description having correct populations but inaccurate coherences, and satisfying local conservation laws, is possible over some of the parameter regimes. Our work highlights the power of semidefinite programming in the analysis of physically consistent LEs in understanding the limits of Markovian descriptions at weak system-bath couplings.

We evaluate the role of quantum coherence as a thermodynamic resource in a noisy, Markovian, one-qubit heat engine. By consuming the coherence of noisy quantum states, we demonstrate that the engine can surpass the classical efficiency limit when operating according to a quantum Otto cycle. The engine's nonclassical nature is demonstrated by its violation of the Leggett-Garg temporal correlations inequality. Amplitude damping increases the extractable work under partial thermalization, thereby increasing the efficiency. In contrast, phase damping increases the extractable work under partial thermalization but reduces the efficiency. We implement the entire Otto cycle in a quantum circuit, simulating realistic amplitude and phase damping channels, as well as gate-level noise. We introduce an operational measure of the circuit's thermodynamic cost to establish a direct link between energy consumption and information processing in quantum heat engines.

In multiparameter quantum estimation, the optimal measurements for different parameters encoded in a quantum state are in general incompatible, giving rise to nontrivial tradeoffs between their attainable levels of precision. Understanding and characterizing such tradeoffs is essential for determining the ultimate precision limits in multiparameter quantum estimation, and it is therefore a central topic in quantum metrology. In this article, we present an approach that precisely quantifies the tradeoff resulting from incompatible optimal measurements in multiparameter estimation. We derive a tight analytical tradeoff relation that determines the ultimate precision limits for estimating an arbitrary number of parameters encoded in pure quantum states. Additionally, we provide a systematic methodology for constructing optimal measurements that saturate this tight bound in an analytical and structured manner. To demonstrate the power of our findings, we apply our methodology to quantum radar, resulting in a refined Arthurs-Kelly relation that characterizes the ultimate performance for the simultaneous estimation of range and velocity.

The differential scalar polarizability $\mathrm{\Delta }{\alpha }_0\left(\omega \right)$ of the ${\mathrm{Ba}}^{+}$ $S_{1/2}\text{−}{D}_{5/2}$ clock transition has a zero crossing near 481 nm, which is measured to be 623.603 13(17) THz. From this measurement, we infer a ratio of reduced matrix elements $\langle P_{3/2}\parallel r\parallel S_{1/2}\rangle /\langle P_{1/2}\parallel r\parallel S_{1/2}\rangle =1.41181\left(13\right)$, which provides a stringent test of atomic structure calculations and experimental determination of matrix elements. Additionally, it enables the construction of an accurate approximation to $\mathrm{\Delta }{\alpha }_0\left(\omega \right)$, valid for frequencies up to 450 THz, with only one reduced matrix element, $\langle P_{1/2}\parallel r\parallel S_{1/2}\rangle$, appearing in the model's parametrization. We discuss the achievable accuracy of the model, the application to the assessment of blackbody radiation shifts in ion-based clocks, and the applicability of the approach to other alkaline-earth ions.

In this paper, we extend the quantum-frequency-mixing technology to a ladder-type four-level system and study its effect on electromagnetically-induced-transparency spectra. We find a secondary splitting of Autler-Townes splitting in the probing field transmission spectra, which can be understood by the effective Hamiltonian derived with multimode Floquet theory. The frequency-mixing scheme developed here enables continuous tunability of the resonant frequency between upper levels, which facilitates the broadband sensing of the ac field. Furthermore, by introducing additional periodic driving, we realize an effective model in which two distinct quantum interference effects coexist: interference among Floquet channels and loop interference arising from closed coherent pathways. Both interference effects can be read out from the transmission spectra independently. The changing of the distance between double-splitting peaks represents the interference of Floquet channels, while their asymmetric linewidth broadening is linked to the total effective phase of the loop. This not only provides a complementary readout for extracting the phase of the ac field but also establishes a paradigm for coherent control in multilevel quantum systems.

We demonstrate that quantum-trajectory interference in high-order harmonic generation can be efficiently modified by tailoring the symmetry of orthogonally polarized two-color laser fields via the temporal delay. Numerical simulations based on the three-dimensional time-dependent Schrödinger equation reveal that an appropriate delay enables selective enhancement of short trajectories while suppressing long trajectories. By combining time-frequency analysis with classical analysis, we show that this trajectory selection originates from the symmetry of the driving field, which governs the relative timing of electron ionization and recollision. The resulting trajectory modulation exhibits a robust periodic behavior that is independent of the laser intensity ratio and the atomic species, but strongly dependent on the frequency ratio of the two-color field. An empirical relation is established to characterize the periodicity of the trajectory selection. The demonstrated trajectory-selection mechanism may provide useful insight for future studies of attosecond pulse generation in orthogonally polarized two-color laser fields.

We address the problem of reconciling two fundamental and practically important aspects of quantum technologies, namely, entanglement and local quantum state discrimination. Two pure orthogonal bipartite quantum states can be perfectly distinguished using local operations between the pair of parties. However, the measurement involved completely destroys the entanglement, a crucial resource for quantum technologies, rendering the postmeasurement states nonresourceful for many subsequent quantum tasks. To avoid complete destruction of entanglement, we propose a protocol that allows an arbitrary number of pairs of parties to distinguish between any two orthogonal, entangled, two-qubit pure states using local quantum operations and classical communication, with a success probability greater than that of random guessing, while ensuring that at each step, the individual ensemble states retain a finite amount of entanglement. Our protocol employs the minimum-error state discrimination approach. For demonstrating the retention of entanglement in the ensemble states at each step, we use a specific entanglement measure as well as the concept of entanglement witnessing. For a large family of sets of the two states, the success probability of discrimination can be as close as required to unity while sustaining a finite amount of entanglement at each step of an arbitrarily large sequence of state discrimination.

We investigate the problem of distinguishing between separable and entangled states of two quantum wave packets, one of which falls into a black hole. Intuitively, one might expect the two scenarios to be indistinguishable, since the information carried by one wave packet is hidden beyond the event horizon. We show, however, that fundamental limitations on the localizability of quantum states can render the two scenarios, in principle, distinguishable. Employing tools from quantum state discrimination theory, we analyze a concrete realization and discuss the configurations that maximize the probability of successfully distinguishing between the two cases.

Quantum technologies rely on high-quality resource states, such as maximally entangled or private states, which are indispensable for quantum communication and cryptography. In practice, however, these states are inevitably degraded by noise. Distillation protocols aim to recover high-resource states from multiple imperfect copies, and while stabilizer-based methods have demonstrated high performance in entanglement purification, they have yet to be established for broader tasks such as secret-key distillation. This work introduces a unified framework for stabilizer-based resource distillation in systems of prime local dimension. By formulating stabilizer routines as quantum channels and deriving closed-form expressions for their output, we enable the application of stabilizer operations to general input states and diverse distillation objectives. We identify key invariances in resource measures—such as coherent and private information—and demonstrate how they can be leveraged to significantly reduce the numerical complexity of channel optimization. To illustrate the framework's versatility, we introduce several protocols: gF-IMAX for general fidelity optimization, and (S)CI-IMAX and (S)PI-IMAX for optimizing (smooth) coherent and private information in both asymptotic and one-shot regimes. Our numerical results confirm that these protocols effectively tailor stabilizer channels to specific operational tasks, establishing them as a flexible tool for quantum resource distillation in highly noisy environments.

We show that harnessing daemonic advantage is possible while charging a quantum battery by first time evolving the battery collectively with an auxiliary charger, followed by an energy extraction via tracing out the charger. We define the difference between the minimum daemonic ergotropy and the maximum ergotropy of the battery as the daemonic gap at the time where the ergotropy of the battery is maximum. Considering a harmonic mode as the battery and a qubit as the auxiliary charger interacting via Jaynes-Cummings interaction, we show that the daemonic gap can be closed for specific initial passive states of the battery, including the ground state, truncated mixtures of low-lying states, and canonical thermal states. We further define the daemonic band as the difference between the maximum and the minimum daemonic ergotropy, and show that starting from the ground state of the single-mode battery, the daemonic band collapses. We also show that achieving a complete charging, along with accessing the full daemonic band, is possible for the single-mode battery using all of the other initial states by repeating the charging cycle and maximizing ergotropy in every round. We extend the battery-charger design to a multimode resonator battery and a qudit charger, and demonstrate, for a double-mode battery and a qutrit charger, that repeating the charging cycle is vital for simultaneously charging individual modes of the collective battery.

We consider background gas collision shifts in ion-based clocks. We give both a classical and quantum description of a collision between an ion and a polarizable particle with a simple hard-sphere repulsion. Both descriptions give consistent results, which shows that a collision-shift bound is determined by the classical Langevin collision rate reduced by a readily calculated factor describing the decoupling of the clock laser from the ion due to the recoil motion. We also show that the result holds when using a more general Lennard-Jones potential to describe the interaction between the ion and its collision partner. This leads to a simple bound for the collision shift applicable to any single-ion clock without resorting to large-scale Monte Carlo simulations or determination of molecular potential energy curves describing the collision. It also provides a relatively straightforward means to measure the relevant collision rate.

We introduce and benchmark a robust angularly resolved difference observable $\mathrm{\Delta }$ that isolates continuum electron dynamics in mainbands of RABBITT-like setups. We focus on the regime where the infrared laser intensity is high enough that the freed electron may exchange multiple infrared photons with the probe field, thereby opening higher-order continuum-continuum channels. Full-dimensionality ab initio calculations for hydrogen and helium atoms across a broad range of infrared intensities and photoelectron energies demonstrate that $\mathrm{\Delta }$ reflects the continuum dynamics almost exclusively, with negligible sensitivity to multielectron effects or target-specific details. The close agreement between both targets indicates that the dominant single-electron character of these reactions, previously established for sidebands in the single-photon continuum-continuum regime, persists into mainbands and survives even as higher-order channels become accessible. An analytic model rationalizes these results and provides a direct connection between $\mathrm{\Delta }$ and the infrared laser intensity at the focal spot.

The single-mode approximation (SMA) has been widely employed in ultracold spinor gases, where all spin components share the same spatial mode. By adopting generalized Van Vleck (GVV) perturbation theory, we achieve a relative error of ${10}^{-6}$ in the ground-state energy with a reduced effective Hilbert space dimension of $\sim {10}^3$ for two spin-1 bosons confined in a one-dimensional hard-wall trap. With the accurate GVV method, we explore the validity of the SMA across ground-state properties and quench spin dynamics for two ${}^7\mathrm{Li}, {}^{87}\mathrm{Rb}$, or ${}^{23}\mathrm{Na}$ atoms. Numerical results show that the quadratic Zeeman energy $q$ provides a powerful control knob: by increasing $\left|q\right|$, the fidelity between the spin components in the ground state gradually decreases, leading eventually to the breakdown of the SMA (due to the competition between the kinetic energy and the quadratic Zeeman energy). Quench spin dynamics with abruptly increased $q$ further reveals multiple resonances, where the SMA-predicted micromotion and beyond-SMA macromotion appear simultaneously. These results point to a direction to investigate the quantum spin-mixing dynamics beyond the SMA, particularly in recent experiments of strongly interacting spin-1 atomic gases.

We investigate the rotational phase diagram of a quasi-two-dimensional, weakly interacting Bose-Einstein condensate confined in power-law and hard-wall trapping potentials. For weak interactions, the system undergoes discontinuous transitions between multiply quantized vortex states as the rotation frequency of the trap increases. In contrast, stronger interactions induce continuous phase transitions toward mixed states involving both singly and multiply quantized vortex states. A central result is the qualitative (and experimentally observable) difference between power-law and hard-wall confinement: In hard-wall traps the leading instability always involves states with nonzero density at the trap center, whereas in power-law traps the density vanishes as the rotation frequency increases. The two different types of confinement give rise to scaling properties in the derived phase diagrams.

We investigate the dynamics of antiferromagnetic dimers within a Rydberg atom chain in the regime where laser detuning compensates for nearest-neighbor (NN) interactions. Using an effective PXQ model, we demonstrate that the associated Hilbert space decomposes into disconnected dimer-conserving subspaces. The classification of these subspaces is provided, and the computational basis states spanning them are identified. Through a combination of analytical mapping and numerical simulations, we compare the dynamics of the PXQ model with those of the full Rydberg atom chain. The deviations are attributed to two factors: laser-induced leakage from the constrained Hilbert subspace and the influence of long-range interactions beyond the NN limit. Our results indicate that subspace leakage can be mitigated by increasing the NN interaction strength. While this simultaneously amplifies the effects of long-range interactions, the conservation of the dimer number remains. Our study opens up possibilities for exploring the dynamics of antiferromagnetic dimers using the Rydberg atom quantum simulator.