We show that Fibonacci time quasicrystals can be approximated by temporal supercells, which capture the nonperiodic but self-similar modulation in an analytically tractable form. This reveals a fractal hierarchy of instability gaps, indexed by the wave number $k$, in which wave energy is amplified exponentially. These estimates are validated by the observation of super $k$ gaps: instability regions that are independent of the duration of the temporal supercell. This approach predicts the regions of parametric amplification and provides arbitrarily accurate estimates of the energy growth rate.

Squeezing has attracted increasing attention as a valuable resource for controlling open quantum systems. In this work, we investigate the dynamics of two-level atoms coupled to a dissipative squeezed cavity field. Going beyond the extensively studied scenario of squeezed waveguides, we focus on a purely local atom-cavity coupling, for which photon-mediated coherent interatomic interactions are absent. Remarkably, we find that atomic entanglement can still be generated and maintained in this setting. On the theoretical side, we analytically reveal a multiple degeneracy of the Liouvillian superoperator at zero eigenvalue, for both zero and finite temperatures, which leads to a steady state that depends sensitively on the initial condition. Our results enrich the understanding of squeezed open-system dynamics and may stimulate further studies toward quantum information processing based on engineered squeezed environments.

Quantum mechanics predicts deviations from exponential decay at short and long times, yet experimental evidence is limited. We report a power-law tail after $\sim 10$ lifetimes in two fluorescent compounds (erythrosine B and eosine Y), confirmed by two detectors probing distinct bands but yielding different power coefficients. The data match a divergent but normalizable spectral density, and theory predicts oscillations as a future test. A general result is that, in multichannel quantum mechanics (and quantum field theory) decay, the lifetime is universal, but the late-time deviations are channel dependent (or band dependent), a feature consistent with our data.

Nitrogen-vacancy (NV) centers in diamond are pivotal for quantum sensing and information processing due to the exceptional spin and optical properties at ambient conditions. In this study, the synthesis of NV centers in nitrogen-rich diamond was systematically investigated using highly charged Argon ions (${\mathrm{Ar}}^{7+}$ at 1.89 MeV and ${\mathrm{Ar}}^{11+}$ at 2.97 MeV) combined with vacuum annealing. The results demonstrate that NV center production is nonmonotonically dependent on implantation fluence, with an optimized yield achieved at a moderate fluence of approximately ${10}^{13}$ ions/cm². Molecular dynamics simulations elucidate the microscopic evolution of vacancy generation, NV formation, and the vacancy cluster formation at excessive fluence. Furthermore, the spatial inhomogeneity of NV distribution near irradiation boundaries and unirradiated areas is mainly attributed to ion scattering effects and beam scanning during implantation. These findings provide a mechanistic understanding and practical guidelines for optimizing NV center fabrication via heavy-ion irradiation for quantum applications.

Quantum droplets (QDs) in weakly interacting ultracold quantum gases are typically characterized by mean-field theories incorporating Lee-Huang-Yang (LHY) quantum fluctuations under simplified zero-range interaction assumptions. However, bridging these models to broader physical regimes like superfluid helium requires precise understanding of short-range interatomic interactions. Here, we investigate how finite-range interactions—next-order corrections to zero-range potentials—significantly alter QD mechanics. Using a consistent effective theory, we derive an analytical equation of state (EOS) for three-dimensional bosonic mixtures under finite-range interactions at zero temperature. Leveraging the Hubbard-Stratonovich transformation, we demonstrate that interspecies attraction facilitates bosonic pairing across components characterized by the nonperturbative parameter of $\mathrm{\Delta }$, leading to nonuniversal LHY terms that encode short-range interaction details while recovering previous universal QD EOS in the zero-range limit. Extending superfluid hydrodynamic equations for two-component systems, we predict fractional frequency shifts in breathing modes induced by these nonuniversal terms. Experimental observation of these shifts would reveal critical insights into QD dynamics and interatomic potential characteristics.

We present a comprehensive study of different phase transitions in the Dicke model incorporating both anisotropy and dissipation. We begin with a concise review of the quantum phase transition in this setting, highlighting how these two parameters shift the critical point. We then perform a detailed investigation of the transition from ergodic to nonergodic phases by analyzing the eigenvalue and eigenvector properties of the Liouvillian with the aid of scaling of the Liouvillian gap and the average participation ratio. Our results show that the eigenvector properties of the Liouvillian are consistent with its spectral characteristics, leading to a phase diagram that has similarities to the closed counterpart. In particular, the steady-state properties are associated with the quantum phase transition, whereas the decaying modes retain signatures of the ergodic to nonergodic transition. Furthermore, we demonstrate that the Liouvillian gap exhibits distinct scaling behaviors in these two phases. Finally, we extend our study to the driven case by applying a Thue-Morse quasiperiodic drive. In this case, we find that bosonic dissipation plays a crucial role in stabilizing the prethermal plateau, offering an effective mechanism to halt the heating effect arising from the quasiperiodic drive.

Quantum reservoir computing (QRC) uses quantum dynamics to efficiently process temporal data. In this work, we investigate a QRC framework based on two coupled Kerr nonlinear oscillators, a system well suited for time-series prediction tasks due to its complex nonlinear interactions and potentially high-dimensional state space. We explore how its performance in forecasting both linear and nonlinear time series depends on key physical parameters—input drive strength, Kerr nonlinearity, and oscillator coupling—and analyze the role of entanglement in improving the reservoir's computational performance, focusing on its effect on predicting nontrivial time series. Using logarithmic negativity to quantify entanglement and normalized root-mean-square error to evaluate predictive accuracy, individual parameter sweeps show that optimal performance occurs at moderate but nonzero entanglement. Furthermore, an aggregated binned analysis reveals that this moderate entanglement is consistently associated with the optimal average predictive performance across the parameter space, an observation that persists up to a threshold in the input frequency. This relationship persists under some levels of dissipation and dephasing. In particular, we find that higher dissipation rates can enhance performance. These findings contribute to the broader understanding of quantum reservoirs for high performance, efficient quantum machine learning, and time-series forecasting.

The atomic response to an ultraintense driving field produces a characteristic high-harmonic spectrum featuring a rapid drop in intensity for the lower harmonics, followed by a plateau and a sharp cutoff. This response vanishes for circularly polarized classical drivers, a limitation that can be overcome by introducing quantum features into the driving field. In this work, we show that squeezed highly elliptically polarized drivers not only enable the high-harmonic generation (HHG) process in classically forbidden regimes of large ellipticity, but also yield highly elliptical harmonic radiation with pronounced super-Poissonian photon statistics. Moreover, we show that the HHG spectral features encode information about the quantum nature of the driving field, revealing the presence of its squeezed field fluctuations. By analyzing the HHG spectral intensity dependence as a function of the driver's ellipticity and squeezing orientation, we identify a means to probe the driving field's quantum properties that intrinsically lie in the high-photon-number regime.

Recent technological advances have enabled quantum light to reach the strong-field regime, opening the door to nonlinear quantum light-matter interactions, yet its role in air lasing remains unexplored. Here, we explore its potential impact on air lasing by studying the population inversion between the $B^2{\mathrm{\Sigma }}_u^{+}(v^{″}=0)$ and $X^2{\mathrm{\Sigma }}_g^{+}(v=0,1)$ states of ${\mathrm{N}}_2^{+}$ across pump wavelengths from 300 to 1200 nm using full quantum density matrix simulations. Our results show that quantum light generates a markedly stronger population inversion than coherent (classical) light at pump wavelengths near 380 and 1000 nm under the pump conditions of an intensity of $I=0.4\times {10}^{14}$ ${\text{W/cm}}^2$ and a pulse duration of 30 fs. This enhancement arises from the broader amplitude fluctuations of quantum light, which contain more high-field components and thereby induce stronger electronic-state coupling. Moreover, population inversion induced by quantum light exhibits a more pronounced wavelength dependence than that driven by coherent light, owing to the selective enhancement of distinct electronic-state coupling at different pump wavelengths. By incorporating molecular rotation, we further find that, for pump intensities ranging from $I=0.4\times {10}^{14}$ to $1.2\times {10}^{14}$ ${\text{W/cm}}^2$, BSV light produces population inversion over a broader range of rotational quantum numbers than coherent light. In this work, we reveal the unique capability of quantum light to modulate the population dynamics of air lasing, offering a pathway to produce stronger and broader lasing.

The structure of circular polarization singularity lines ($C$-lines) of the electromagnetic field and Möbius optical ribbons near a subwavelength silicon nanoparticle of toroidal shape is analyzed for a plane monochromatic uniformly elliptically polarized wave incident in two cases: with its wave vector parallel to the torus axis and lying in the plane of the torus' generating circle. Depending on the parameters of the incident wave, between two and six closed $C$-lines are observed near the nanoparticle. Patterns of changes in their size and shape, as well as the fraction of points of topological types lemon, star, and monstar on each $C$-line, are analyzed. The twist coefficient of Möbius optical ribbons constructed around points of different topological types on the $C$-lines is investigated for the case in which the center of the polarization ellipse moves along a small-radius circle centered at a $C$-line point, the plane of which coincides with the plane of the degenerate ellipse (circle) of polarization at that point.

Achieving efficient three-dimensional feedback cooling of levitated nanoparticles is a key requirement for precision sensing and quantum control in levitated optomechanics. Here we demonstrate three-dimensional optical feedback cooling of a levitated nanoparticle using an interference-enhanced optical force generated within a single beam path. In this scheme, a weak auxiliary field copropagates with the trapping tweezer and interferes with it to produce a tunable optical force that enables cold damping along all three center-of-mass motional axes without additional beam paths or trap reconfiguration. Using this approach, we cool a 142-nm-diameter silica nanoparticle in high vacuum to effective temperatures of 625.8, 711.6, and 19.9 mK along the $x, y$, and $z$ directions, respectively, at a pressure of $8.5\times {10}^{-6}$ mbar. The cooling dynamics and their dependence on feedback gain and pressure are well described by a cold-damping model. Because the feedback force is generated optically, the scheme does not rely on electrical actuation and is directly compatible with neutral particles. These results establish interference-based optical forces as a simple and broadly applicable mechanism for three-dimensional feedback control in levitated optomechanics, with a clear pathway toward the quantum regime under improved vacuum and detection conditions.

We propose a fractional physics-informed neural network (fPINN) framework to investigate the propagation dynamics of necklace beams trapped in an annular potential within a saturable nonlinear medium. The interplay among fractional-order diffraction, potential confinement, and nonlinearity gives rise to robust necklace beams carrying an arbitrary fractional orbital angular momentum. Using the fPINN approach, we systematically explore the propagation dynamics of such beams. While the annular potential effectively suppresses radial expansion, the combination of fractional diffraction and saturable nonlinearity significantly enhances the beam's robustness. Our findings unveil physical behaviors in fractional nonlinear optical systems and highlight the effectiveness of fPINNs for solving complex fractional-order nonlinear problems.

Coherent, spectrally modulated sideband radiation results from interaction of a moderately intense picosecond laser pulse with nearly resonant emitters. We theoretically analyze a situation where these emitters are excited argon atoms arranged in a rhombic gridiron formation. This latter is generated in a relatively dense gas by femtosecond laser filamentation at a small-angle crossing of two identical pump laser beams, when an interference-borne intensity comb swipes along the crossing area. The geometry and content of the excitation gridiron are controlled by the beam radius, the crossing angle, and the phase delay between the two pump pulses. The picosecond probe pulse engages multiple transitions in the distributed excited argon atoms and produces coherent sideband radiation of considerable complexity, from which various coherent frequency arrays can be extracted. In one extraction scheme, the sideband radiation is collected and spectrally analyzed on a remote output screen, which is parallel to the gridiron plane. The resulting signal depends on the wavelength and two spatial coordinates; this three-variable distribution makes for a four-dimensional coherent hyperspectral interference pattern, whose three-dimensional sections (two-variable distributions) can be rendered by observation slits on the screen. We traced the modifications of such a section as controlled by the parameters of the pump pulses and the probe pulse. In particular, the positions of the bright spots in the patterns have been quantitatively associated with the crossing angle of the pump beams and the radius of the probe beam.

Elegant Bell inequality is well known for its distinctive property, being maximally violated by maximal entanglement, mutually unbiased bases, and symmetric informationally complete positive operator-valued measure elements. Despite its significance in quantum information theory demonstrated based on its unique violation feature, it remains the only known one with the characteristic. We present a method to construct Bell inequalities with violation feature analogous to elegant Bell inequality in higher local dimensions from a simple, analytic quantum bound. A Bell inequality with the generalized violation feature is derived for the locally three-dimensional case. It exhibits larger violation than existing Bell inequalities of similar classes, including the original elegant Bell inequality, while requiring arguably small number of measurements.

Accessible information of an ensemble, together with its Holevo bound, plays an essential role in quantum information science. Here, we report an alternative upper bound for accessible information based on a relation between accessible information and entanglement. Our bound can tighten the Holevo bound and even coincides with the accurate values of accessible information in some special cases. Since accessible path information provides a natural measure for particle character, our bound leads to a wave-particle duality relation that strengthens previous results. The alternative upper bound of accessible information of an ensemble and the method of deriving our bound may have applications in other areas of quantum information science and quantum foundational theory beyond wave-particle duality.

Noiseless linear amplifiers serve as an effective means to enable long-distance continuous-variable (CV) quantum key distribution (QKD), even under realistic conditions with nonunit reconciliation efficiency. Separately, unitary averaging has been suggested to mitigate some stochastic noise, including phase noise in continuous-variable states. In this work, we combine these two protocols to simultaneously compensate for thermal-loss effects and suppress phase noise, thereby enabling long-distance CV QKD that surpasses the repeaterless bound, the fundamental rate-distance limit, for repeaterless quantum communication systems.

Experiments to determine transition frequencies in the hydrogen atom represent some of the most precise spectroscopic measurements and are at a higher level among simple atomic systems. The most persistent measured value in hydrogen is the energy interval corresponding to the $1s-2s$ two-photon transition. The achieved experimental precision is several parts of ${10}^{-15}$ and has not changed over the last two decades. Although repeated experiments in 2011 and 2013 have improved the accuracy by several times, the frequency value has not changed significantly. On this basis, the frequency of the $1s-2s$ transition holds pivotal for determining physical quantities such as the Rydberg constant and the proton charge radius. Theoretical efforts to study in detail the effects that might influence such precise measurements have not revealed significant contributions. The present work revises the theoretical analysis of the line contour asymmetry and its influence on the determination of the two-photon absorption transition frequency, taking into account the theoretical achievements of recent years in this direction. It is shown that the asymmetry of the observed profile can lead to a $1s-2s$ transition frequency shift at the level of modern experimental accuracy. The found frequency shift is consistent with the line shape model contribution that forms the error budget of the experimental measurements. Adjustment can be carried out on the basis of the asymmetric profile that has become standard in recent years.

We present a combined experimental and theoretical study of degenerate four-wave mixing (FWM) in a thermal rubidium vapor on the ${\mathrm{D}}_2$ line. The experiment employs a forward phase-matched geometry with a single laser, where the atomic density—and thus the optical depth—is controlled via the cell temperature. We measure the generated FWM signal across a wide range of densities, observing a characteristic suppression and saturation at high optical depths. To explain these phenomena, we develop a theoretical model based on a semiclassical treatment of the atomic response that includes nonlinear propagation effects. The model's core is a recursive Liouville equation derived from a systematic expansion of the system's density matrix, which provides an analytical solution for the optical coherence and the generated field in a closed four-level excitation loop. This theoretical framework shows excellent agreement with the experimental data across all densities. By confronting theory and experiment, we demonstrate that our model simultaneously captures the roles of absorption, propagation, and interference in shaping the nonlinear optical response, showing that the observed suppression of the FWM signal at high atomic density arises from the combined action of these competing mechanisms.