We investigate how interlayer coupling shapes high-harmonic generation (HHG) in AA-stacked bilayer ${\mathrm{WS}}_2$ using real-time time-dependent density functional theory and semiconductor Bloch equations. The bilayer harmonic yield is found to depart from the coherent layer-number enhancement expected for independent layers, with the departure growing continuously as the interlayer distance is reduced. We trace this behavior to coupling-induced band splitting, which opens two electron-hole recombination pathways whose relative dynamical phase is set by the interlayer coupling. As the coupling increases, the two pathways evolve from nearly constructive toward partially destructive interference. Time-frequency analysis and two-color field probing show that their recombination timing shifts accordingly. Interlayer coupling thus provides continuous structural control over recombination-pathway interference, allowing the amplitude, phase, and timing of solid-state high-harmonic emission to be tailored.

The electron shell of Thorium ions with a $M1\left(8.4\mathrm{eV}\right)$ transition between the electron states and the doublet of the ${}^{229}\mathrm{Th}$ nucleus ground state with a similar transition represent two two-level systems spatially inserted one within the other. In the case of the relative proximity of the energies of these transitions, weakly damped energy oscillations can be excited between these two-level systems, namely, multiple coherent energy transfers from the electron shell to the nucleus and vice versa. This process in ${}^{229}\mathrm{Th}$ ions does not require a resonant (within the width of the levels) coincidence of the transition energies due to the relatively high interaction energy of the electron and nuclear currents and extends the energy range for the ${}^{229m}\mathrm{Th}(3/2^{+},8.4\mathrm{eV}$) isomer excitation via an electron bridge. The electron shell, transitioning between two electron states, “breathes,” periodically decreasing and increasing in size. Furthermore, the system under consideration is transformed into a nuclear quantum battery when exposed to coherent laser radiation. To “charge” the battery, i.e., to excite ${}^{229m}\mathrm{Th}$, one can use developed methods for charging quantum batteries, in particular, the coherent excitation of the electron shell followed by a coherent transfer of excitation energy to the nucleus (the coherent electron bridge). This opens the way for the design of a ${}^{229}\mathrm{Th}$ nuclear quantum battery at the current level of technological development.

We present a fully quantum-mechanical comparison of two-photon absorption (TPA) probabilities for a single pulse among three photon states: an entangled photon-pair state (EPPS), a separable photon-pair state (PPS), and a multimode coherent state (MCS). While the EPPS and PPS are commonly compared in entangled two-photon absorption (ETPA) theories, the MCS, i.e., the quantum-optical description of pulsed laser light, has not been directly included in such comparisons. By focusing on the two-photon component of MCS, we show that the TPA probability for the two-photon component of MCS is strictly bounded above by that for the PPS, with the ratio governed by the Poisson distribution. This establishes a rigorous hierarchy of single-pulse TPA efficiency for $n\lesssim 1$: EPPS $>$ PPS $>$ MCS. The dominant contribution to the efficiency gap between ETPA and pulsed laser TPA originates from the photon statistics, providing a quantum-optical explanation for the enormous difference observed experimentally.

Optical nonreciprocity with both reversible transmission direction and broad frequency tunability is highly desirable for flexible control of light propagation in integrated photonic systems. Here, we propose a scheme to realize reconfigurable and frequency-tunable optical nonreciprocity in a coupled dual whispering-gallery-mode resonator with optomechanical interactions. A strong directional driving field is selectively applied to the clockwise mode of one cavity and kept fixed for both probe propagation directions. For forward propagation, the probe excites the counterclockwise mode of the adjacent cavity coupled to the strongly driven clockwise mode. Near the quantum critical point, the resulting strong coupling between the lower polariton and the adjacent cavity mode induces Autler-Townes (AT) splitting, enabling nearly perfect forward-direction transmission. In contrast, for backward propagation, the probe couples to the oppositely propagating mode without the same pump-enhanced optomechanical interaction, so that the AT effect is absent and the resonant probe is strongly absorbed. By tuning the incident-light frequency to the AT-split resonances, the transmission and absorption directions can be reversed, realizing reconfigurable optical nonreciprocity. Moreover, the operating frequency can be continuously tuned by varying the effective polariton-cavity coupling, which shifts the AT-split resonances. A tuning range exceeding 25 times the optical-cavity linewidth can be achieved. Numerical results agree well with the derived analytical frequency-matching conditions. This work provides a feasible theoretical strategy for the design of tunable nonreciprocal integrated photonic devices.

Photon blockade is a phenomenon in which the presence of system nonlinearity causes the output to consist of single photons, which has been extensively studied in point-atom systems, but it has barely been explored in giant-atom ones. In this paper, we propose a giant-atom-mediated photon-blockade scheme based on two-cavity and three-cavity systems with a driving field applied to the first cavity. We show that simultaneous unconventional photon blockades (UPBs) cannot occur in the point-atom system (the atom couples only to the leftmost cavity) because a cavity with a single path always exists. In contrast, the spatially extended nature of the giant atom enables coupling to multiple cavities and allows for the introduction of a phase and coupling strength. Consequently, simultaneous UPBs in multiple cavities can be obtained due to multipath destructive interference. Moreover, by manipulating the detuning, we observe simultaneous conventional photon blockades in multiple cavities. Finally, we study simultaneous two-photon blockades in a point-atom multiple-cavity system.

Bosonic modes provide a promising platform for quantum batteries as a result of their unbounded energy spectrum. However, the energy that can be stored during a coherent charging process is limited due to coherent oscillations between the charger and battery. In this work, we show that by introducing a slow quench in the interaction between a coherently driven charger mode and a quadratic oscillator battery, the maximum stored energy and maximum battery power scale algebraically with the quench duration, with exponents controlled by the ramp profile. This finding implies that, quite counterintuitively, slower quenches lead to faster charging. Such a quench suppresses coherent energy oscillations between the battery and the charger, allowing an unbounded increase in power. We further show that, in the ideal closed protocol, the stored energy is fully extractable as ergotropy, while charger dissipation converts the algebraic enhancement into a finite-time scaling window with an optimal quench duration. We also show that the temporal-extensive scaling occurs in a broader context by mapping the system to a coherently driven Tavis-Cummings battery. Finally, we discuss experimentally accessible signatures in superconducting circuit quantum electrodynamics and organic microcavity platforms.

Quantum states with sub-Planck features exhibit sensitivity to phase-space displacements beyond the standard quantum limit, making them useful for quantum metrology. In the context of the SU(1,1) group, sub-Planck features have been constructed through the superposition of four Perelomov coherent states on the hyperbolic plane (the SU(1,1) compass state). However, these structures differ in scale along different phase-space directions (anisotropic features), resulting in nonuniform sensitivity enhancement to phase-space displacements. Here, we construct $N$-component compass states, which are obtained by superposing $N\ge 6$ SU(1,1) coherent states with an even total number, evenly arranged along a circular path on the hyperbolic plane; that is, all components lie at the same distance from the origin and have equal angular spacing of $\frac{2\pi }{N}$. We observe that these generalized SU(1,1) compass states exhibit isotropic sub-Planck structures, leading to an isotropic enhancement in sensitivity to phase-space displacements that progressively increases with larger $N$. These states are directly relevant to quantum platforms supporting Kerr-type interactions between two bosonic modes, where the underlying SU(1,1) dynamical symmetry enables the generation of multicomponent SU(1,1) compass states. Specifically, the compact evolution of SU(1,1) coherent states under the considered dynamics enables the generation of multicomponent SU(1,1) compass states at specific times. We also investigate the effects of thermal decoherence on these multicomponent compass states within a frequency-resolved Lindblad framework, demonstrating the evolution and degradation of their nonclassical signatures.

We propose a method for realizing a high-fidelity and robust controlled-not gate in a Si double-quantum-dot system. The Hamiltonian of the system is first reduced to a block-diagonal form, dividing it into two individual subsystems. Given the interdependence of certain parameters between these subsystems, we develop two techniques, detuning modulation and magnetic-field rotation, to perform a robust identity operation in one subsystem and a reliable not gate in the other subsystem. Numerical results validate the feasibility of this methodology, demonstrating that the controlled-not gate we design still maintains very high fidelity over a relatively wide range of pulse duration deviations. Furthermore, the pulse shape we adopt is a common square wave, which is easy to obtain in practice. This work can provide a general framework for the realization of reliable quantum computations in silicon-based quantum-dot systems.

Sampling experiments provide a viable route to show quantum advantages of quantum devices over classical computers in well-defined computational tasks. However, quantum devices such as boson samplers are susceptible to various errors, including stochastic errors due to fabrication imperfections. These cause the implemented unitary operations to deviate randomly from their intended targets, following distributions with finite variance. While full-scale quantum error correction remains challenging in the near term, quantum error mitigation schemes have been devised to estimate expectation values, but it is unclear how these schemes would work for sampling experiments. In this work, we demonstrate that, given access to multiple unbiased stochastic unitaries, it is possible to mitigate the effect of these errors in sampling experiments. We adopt the unitary averaging protocol, which employs multiple unbiased stochastic boson samplers to generate a distribution that approximates the ideal boson sampler distribution as the number of samplers increases. We derive a rigorous upper bound on the trace distance between the output probability distributions induced by invertible vacuum-heralded networks based on the Schur-Weyl duality. This result can be seen concretely as an error mitigation scheme in sampling experiments against stochastic errors. On a broader level, it suggests a path towards understanding error mitigation for sampling experiments and developing analysis tools for photonic circuits incorporating measurements and feed-forward. We further provide other applications of unitary averaging, including its use in implementing the linear combination of unitaries and benchmarking fabrication repeatability in linear optics.

We investigate the overall optomechanical force experienced by a macroscopic lossy object in free space under external quantum illumination. To this end, utilizing the modified Langevin noise formalism, we derive the time-averaged expectation value of the Maxwell stress tensor for a nonequilibrium scenario in which the incoming scattering field is prepared in an arbitrary mixed quantum state, while the medium-assisted field is maintained in local thermal equilibrium. In the limit of full radiation-matter thermal equilibrium, our expression exactly recovers the well-known fluctuation-dissipation relation governing the Casimir effect, and under coherent illumination it yields the standard classical radiation pressure. We demonstrate that by driving the scattering field with an anisotropic, multimode squeezed vacuum state, the spatial profile of the electromagnetic quantum fluctuations can be engineered to exhibit broken rotational symmetry, thereby inducing a fluctuation-driven mechanical force acting on the object. Such mechanical interaction is generated in the strict absence of a mean field $\langle \widehat{\mathbf{E}}\rangle =0$ and is governed exclusively by second-order field correlations $\langle {\widehat{\mathbf{E}}}^2\rangle$, unlike classical optical radiation pressure dictated by the squared mean field ${\langle \widehat{\mathbf{E}}\rangle }^2$. Applying this exact formulation to a homogeneous lossy sphere, we demonstrate the experimental feasibility of the effect using realistic material parameters and optical estimations. Ultimately, we establish a general formalism for macroscopic quantum optomechanics that operates beyond the constraints of thermal equilibrium, enabling the prediction of regimes where the structured force operates without classical carriers, providing a theoretical framework to systematically investigate the mitigation of radiation-pressure shot noise and macroscopic spatial decoherence.

We study how the Lamb shift of a static atom is modified when a nearby planar body rotates rigidly about its normal while the atom is held at a fixed distance $a$. We derive a general formula for the shift in terms of the angularly Doppler-shifted reflection coefficients of the surface, valid for any axially symmetric planar material. Expanding the result to second order in the angular velocity $\mathrm{\Omega }$, we identify two independent contributions associated with the orbital and spin components of the electromagnetic angular momentum. The orbital contribution, proportional to ${\left(\mathrm{\Omega }\rho \right)}^2$, reproduces locally the Lamb shift induced by a surface translating at the tangential velocity $\mathrm{\Omega }\rho$, whereas the spin contribution, proportional to ${\left(a\mathrm{\Omega }\right)}^2$, originates from the rotational Doppler shift of the photon helicity and survives even on the rotation axis. We first illustrate the formalism using a graphene sheet and then apply it to finite-thickness Drude and plasma conductors and to doped semiconductors. Rotation enhances the Casimir-Polder interaction for graphene and metallic surfaces, whereas it weakens it for doped semiconductors, depending on whether the carrier plasma frequency reaches the near-field scale $1/a$. Above a threshold angular velocity, the atomic level also acquires a finite linewidth, providing a spectroscopic signature of quantum friction. Furthermore, rotation induces a component of the Casimir-Polder force, which is perpendicular to both the standard normal attraction and the tangential quantum-friction force.

The ratio $R$ of helium double-to-single ionization was determined with uncertainties below $1\%$ for 25, 120, and $225\mathrm{MeV}/\mathrm{u} {\mathrm{Fe}}^{26+}$ and $5\mathrm{MeV}/\mathrm{u} {\mathrm{O}}^{7+}$. The experimental results were compared with present theoretical calculations based on the semiclassical approximation and the independent electron model. Combined with the available historical data for highly charged projectiles, the results were analyzed in reduced-velocity representations. The present data lie within the perturbative two-step regime and fit well with the semiempirical reduced-velocity scaling. Reappraisal of the historical data further indicates that the previously reported deviations do not provide a consistent experimental basis for a breakdown of reduced-velocity scaling. For the ratio $R$ within the perturbative two-step regime, the available data therefore do not constitute robust experimental evidence for higher-order contributions.

Multiphoton ionization driven by combined midinfrared (MIR) and vacuum-ultraviolet (VUV) fields can proceed efficiently even when the VUV photon energy lies below the ionization threshold, provided that additional MIR photons bridge the energy gap. When using a few-cycle MIR pulse, its large bandwidth enables a two-color regime in which two distinct ionization pathways, which differ by one absorbed MIR photon, reach the same final photoelectron energy and therefore interfere coherently. Using the hydrogen atom as an example and solving the time-dependent Schrödinger equation in the combined fields, we show that the total ionization yield exhibits a pronounced phase-delay dependence, oscillating twice per MIR optical cycle as the relative VUV-MIR phase is varied. This subcycle modulation is a direct signature of interference between the competing multiphoton pathways. In an orthogonal-field geometry, the same pathway interference imprints a strong, phase-dependent modulation on the low-energy photoelectron momentum distribution, enabling substantial redistribution and redirection of emitted photoelectrons. These results establish a different coherent-control scheme for steering photoelectrons via interference of multiphoton pathways in two-color strong-field ionization, and provide a simple platform for extending phase-controlled electron shaping to more complex targets.

We introduce a coupled-channel method for elastic three-body scattering in systems of identical bosonic alkali-metal atoms. The approach relies on the numerically exact two-body off-the-energy-shell transition matrix, constructed from realistic multichannel molecular interaction potentials that support many bound states. By rigorously accounting for this off-shell structure, the method captures both the short-range physics as well as multichannel couplings characteristic of alkali-metal potentials without resorting to model pseudopotentials. The central output is the complex three-body scattering hypervolume—the three-body analog of the two-body scattering length—which we obtain with controlled and verifiable numerical accuracy. As a realistic benchmark, we apply our framework to spin-polarized potassium-39, performing full coupled-channel three-body scattering calculations and extracting the hypervolume over experimentally relevant conditions. The method is general and transferable to other atomic species and interaction models featuring deep molecular potentials with an arbitrarily large number of bound states.

Optical vortex lattices are fundamental to advancing high-capacity spatial multiplexing and multiparticle manipulation. However, transporting these complex arrays over extended free-space distances remains a challenge, as natural transverse diffraction inevitably triggers intense coherent crosstalk that degrades predefined topological structures. Here, we demonstrate a multiparameter modulation strategy that mitigates this propagation constraint through initial-phase engineering. By introducing a designed optical-axis offset between adjacent lattice cells, the resulting field acquires a controlled phase relation that promotes localized destructive interference, forming a dark grid that reduces transverse overlap and coherent intercell coupling. This mechanism is experimentally realized through liquid-crystal photoalignment, achieving an array-generation efficiency of up to 90% without the pixelation-induced zero-order background associated with conventional spatial light modulator implementations. Under this collective transverse confinement, the generated scalar vortex-antivortex and conjugate vectorial vortex lattices preserve information-bearing central vortex units over extended propagation distances. Their phase singularities remain identifiable throughout the structured local-field evolution, and the conjugate vectorial vortex lattice retains a discernible alternating polarization organization. Following a localized obstruction, the vectorial lattice recovers the phase- and polarization-encoded organization of its central region. This geometric phase platform is electrically tunable and scalable to higher-order topological states such as optical skyrmions, offering a reliable hardware architecture for advanced structured light applications.

We investigate the equilibrium quantum phase transition and critical phenomena in a Tavis-Cummings model that incorporates both an antisqueezing term and the $A^2$ term (the square of the vector potential). The antisqueezing term substantially reduces the critical coupling required for the phase transition, enabling the transition to occur without the need for ultrastrong atom-field coupling. Interestingly, when the $A^2$ term is included, the transition displays a reversed directionality: as the atom-field coupling increases, the system transitions from the superradiant phase back to the normal phase. We find that both ground-state entanglement and quantum superposition display correspondingly reversed behavior in the presence of the $A^2$ term. Moreover, we show that this reversed phase transition is accompanied by a dynamic crossover from chaotic to integrable behavior.

We develop a theory for the quantum-fluctuation spectrum of nonlinearly interacting whispering-gallery modes in a cylindrical microresonator with small radius variations. We show that the nonuniform axial spatial distribution of the modes can be used to optimize the coupler position, enabling both efficient pumping of the central mode and strong squeezing of correlated photon pairs in the sidebands.

Integrating quantum information protocols with metasurfaces opens new opportunities for nonlocal and high-capacity optical information processing. Here, we experimentally demonstrate remote multichannel vectorial meta-holography enabled by polarization entanglement between spatially separated photon pairs. By combining a compact, phase-robust Sagnac entanglement source with a full-Jones-matrix dielectric metasurface, we encode multiple elementary holographic contents and conditionally retrieve their individual and composite outputs through joint input-output polarization projections. The selected holographic content is identified through polarization-resolved coincidence measurements, whereas local single-channel detection alone does not provide access to the corresponding conditional channel information. Compared with single-channel detection, the coincidence reconstruction achieves a signal-to-noise ratio enhancement of 4.74 dB. This work establishes a compact quantum-correlated metasurface platform for multichannel holographic information processing, with potential applications in correlation-gated imaging, encrypted communication, and nonclassical optical information processing.

We investigate the dynamics of a quadratically coupled system under the influence of an external drive applied to the second oscillator, where the coupling facilitates a high-order synchronization with phase locking emerging in the form of $2:1$ between the oscillators. Our analysis reveals a synchronization blockade in the first oscillator, characterized by the complete suppression of conventional $1:1$ phase locking with the drive. Instead the first oscillator exhibits a $2:1$ phase-locking behavior arising from the anharmonicity induced by the quadratic coupling. In contrast, we observe that the directly driven second oscillator synchronizes with the drive, showing $1:1$ phase locking but notably at second-harmonic frequency (${\omega }_2=2{\omega }_d$). A classical mean-field analysis of the corresponding equations of motion reproduces this asymmetric phase-locking geometry, including the two symmetry-related 2:1 phase-locked states of the first oscillator and the 1:1 phase-locked state of the second oscillator. This demonstrates that the phase-locking structure itself can be understood from the nonlinear classical dynamics. The quantum analysis, however, reveals the microscopic origin of the synchronization blockade: the quadratic interaction imposes a two-phonon selection rule that suppresses the conventional single-phonon synchronization channel of the first oscillator. Furthermore, we show that the system exhibits mutual synchronization when both the oscillators satisfy the resonance condition, enabling coherent energy exchange facilitated by nonlinear quadratic coupling. The mutual synchronization shows synchronized regimes and also subtle suppression of synchronized regimes near resonance occurring due to spectral splitting of the energy states. Using perturbation analysis of the master equation within the low-excitation subspace, we analyze steady-state phase distribution and synchronization measures, supported by population statistics and spectral responses. We also propose possible experimental realizations in trapped ions and optomechanical setups. These findings highlight the crucial role of quadratic coupling in enabling nonclassical synchronization phenomena, offering deeper insights for quantum control strategies and the development of quantum information platforms.

Probability backflow is investigated for charged spin-$1/2$ particles in a uniform magnetic field within the lowest-Landau-level approximation. While single-mode Landau states exhibit only weak and nonrobust backflow, it is shown that two-mode interference gives rise to negative probability flux in both the Schrödinger and Pauli formulations. In the Pauli case, orbital and spin contributions to the probability current are explicitly separated, revealing an additional interference mechanism. The external magnetic field is found to act as a tunable control parameter, simultaneously controlling the spatial overlap of orbitals and the spin dynamics. In the two-mode regime, a resonance between orbital mismatch and spin precession leads to an enhancement of backflow. Finite spatial resolution is shown to not suppress the effect within realistic coarse graining. These results establish magnetic-field-controlled quantum backflow in Landau systems as an accessible interference phenomenon.