We demonstrate that the dynamics of quantum coherence serves as an effective probe for identifying dephasing, which is a distinctive signature of many-body localization (MBL). Quantum coherence can be utilized to measure both the local coherence of specific subsystems and the total coherence of the whole system in a consistent manner. Our results reveal that the local coherence of small subsystems decays over time following a power law in the MBL phase, while it reaches a stable value within the same time window in the Anderson-localized (AL) phase. In contrast, the total coherence of the whole system exhibits logarithmic growth during the MBL phase and reaches a stable value in the AL phase. Notably, this dynamic characteristic of quantum coherence remains robust even with weak interactions and displays unbounded behavior in infinite systems. Our results provide insights into understanding many-body dephasing phenomena in MBL systems and reveal a feasible method for identifying and characterizing MBL phases in experiments.

With the increased availability of quantum technological devices, it becomes more important to have tools to guarantee their correct nonclassical behavior. This is especially important for quantum networks, which constitute the platforms where multipartite cryptographic protocols will be implemented, and where guarantees of nonclassicality translate into security proofs. We derive linear and nonlinear Bell-like inequalities for networks, whose violation certifies the absence of a minimum number of classical sources in them. We do so, first, without assuming that nature is ultimately governed by quantum mechanics, providing a hierarchy interpolating between network nonlocality and full network nonlocality. Second we insert this assumption, which leads to results more amenable to certification in experiments.

Dynamical response functions are fundamental quantities to describe the excited-state properties in quantum many-body systems. Quantum algorithms have been proposed to evaluate these quantities by means of quantum phase estimation (QPE), where the energy spectra are directly extracted from the QPE measurement outcomes in the frequency domain. Accurate estimation of excitation energies and transition probabilities with these QPE-based approaches is, however, challenging because of the problem of spectral leakage (or peak broadening) which is inherent in the QPE algorithm. To overcome this issue, in this work we consider an extension of the QPE-based approach adopting the optimal entangled input states, which is known to achieve the Heisenberg-limited scaling for the estimation precision. We show that with this method the peaks in the calculated energy spectra are more localized than those calculated by the original QPE-based approaches, suggesting the mitigation of the spectral leakage problem. By analyzing the probability distribution with the entangled phase estimation, we propose a simple scheme to better estimate both the transition energies and the corresponding transition probabilities of the peaks of interest in the spectra. The validity of our prescription is demonstrated by numerical simulations in various quantum many-body problems: the spectral function of a simple electron-plasmon model in condensed-matter physics, the dipole transitions of the ${\mathrm{H}}_2\mathrm{O}$ molecule in quantum chemistry, and the electromagnetic transitions of the ${}^6\mathrm{Li}$ nucleus in nuclear physics.

We measure the complete set of transition frequencies necessary to laser cool and trap MgF molecules. Specifically, we report the frequency of multiple low-$J$ transitions of the $X{}^2{\mathrm{\Sigma }}^{+}(v^{″}=0,1)\to A{}^2{\mathrm{\Pi }}_{1/2}(v^{\prime }=0)$, $X{}^2{\mathrm{\Sigma }}^{+}(v^{″}=1,2)\to A{}^2{\mathrm{\Pi }}_{1/2}(v^{\prime }=1)$, and $X{}^2{\mathrm{\Sigma }}^{+}(v^{″}=1)\to B{}^2{\mathrm{\Sigma }}^{+}(v^{\prime }=0)$ bands of MgF. The measured $X{}^2{\mathrm{\Sigma }}^{+}(v^{″}=1)\to B{}^2{\mathrm{\Sigma }}^{+}(v^{\prime }=0)$ spectrum allows the spin-rotation and hyperfine parameters of the $B{}^2{\mathrm{\Sigma }}^{+}(v=0)$ state of MgF to be determined. Furthermore, we demonstrate optical cycling in MgF by pumping molecules into the $X{}^2{\mathrm{\Sigma }}^{+}(v=1,2)$ states. Optical pumping enhances the spectroscopic signals of transitions originating in the $N^{″}=1$ level of the $X{}^2{\mathrm{\Sigma }}^{+}(v^{″}=1,2)$ states.

Femtosecond laser filamentation in air presents significant potential for atmospheric scale applications, including remote sensing and lightning control. However, projecting a filament over large distances remains a challenge due to the complex nonlinear propagation dynamics of high-intensity femtosecond pulses. This work demonstrates the generation of an intense ring-Airy-beam femtosecond pulse in air, employing a specially designed phase plate that converts an input quasi-Gaussian beam into the Fourier transform of a ring Airy beam at the front focal plane of a Fourier lens. The high damage threshold of the phase plate enables the corresponding near field of the ring Airy beam at the rear focal plane of the lens to reach a tens-of-gigawatt peak power. This near field subsequently evolves, at a distance of 10 m, into an ionizing filament, capable of ablating an aluminum plate and performing laser-induced breakdown spectroscopy (LIBS). Extending the cm-scale propagation of a ring Airy beam in liquids or glasses, as reported in previous works, to the 10-meter scale with the generation of an ionizing filament, represents a crucial step toward real-world applications of remote LIBS with ring-Airy-beam femtosecond pulses. Experimental observations show a filament length of two meters, corroborating the numerical simulation and expanding the potential to applications that necessitate a long plasma channel. Further numerical simulations indicate the feasibility of controlling the starting point of a filament beyond 100 meters by increasing the focal length of the Fourier lens, opening avenues for fascinating applications in remote sensing and beyond.

The tailored disorder explores light-matter interaction with various functionalities in solar photovoltaic, lasing, structural coloration, and quantum technologies. However, studies are limited to exploring tailored disorder-induced light scattering, while the interactions between emitters and random cavities still need to be analyzed. We demonstrate a significant Purcell-enhanced emission using random cavities in a spatially dispersed silicon (Si) pyramid array. The numerical simulation reveals spatial confinement of electric field intensity in the cavity with substantial Purcell enhancement for an embedded emitter. We experimentally verify Purcell enhancement using localized emitters coupled to Si pyramids, demonstrating fivefold enhanced emission intensity. We achieve a 67% reduction in emission lifetime for random cavity-coupled emitters, which depends on Si pyramid density across the sample, supported with numerical simulations. Our results put forward an amenable approach to tailoring random cavities to manipulate the emission properties of quantum emitters.

We study the intriguing dynamics of surper-regular breathers (SRBs) beyond the Manakov system. These SRB solutions are derived within the nondegenerate context. By employing the Darboux transformation, we obtain the exact expressions of the solutions for the vector SRBs in the coupled Hirota equations with the third dispersion, self-steepening, and inelastic Raman scattering terms. Based on such explicit formulas, we initially study the higher-order effects on their group velocities as well as the growth rate during the linear stage of modulation instability (MI). Additionally, we conduct an exploration of various mode excitations emerging during the nonlinear stage of MI. Our findings indicate that there exist significantly different wave modes from those in the Manakov system or the scalar nonlinear Schrödinger equation (NLSE). In particular, we refine existing formulas connecting the SRBs and MI in the nondegenerate regime, which eliminates the necessity to neglect higher-order terms from the Taylor expansion of $\alpha$. Instead, we have used four different eigenvalues for a more comprehensive description. We also discuss the scalar SRB with two eigenvalues using wave component analysis. We finally excite, via numerical simulation initiated with localized periodic initial conditions, the vector SRBs and their transformed states. This study not only deepens our theoretical comprehension of SRB dynamics, but also illuminates potential avenues for future experimental investigations in this fascinating field.

The capability of near-zero-index media to bypass phase-matching requirements constitutes a promising platform for harmonic generation, which plays a crucial role for the development of compact ultraviolet radiation sources. Here, we investigate third-harmonic generation in near-zero-index heterogeneous nanostructures undergoing collision-driven nonlinear electron dynamics upon pulsed electromagnetic excitation. In particular, we model third-harmonic generation in sodium-aluminum bilayers by perturbatively solving Maxwell's equations in the undepleted pump approximation, finding that such a nonlinear process can become doubly resonant under the sodium and aluminum near-zero-index conditions for pump and third-harmonic waves, respectively. Furthermore, we find that third-harmonic generation is maximized at a peculiar pump incidence angle where attenuated total internal reflection enables surface plasmon polariton excitation at the sodium-aluminum interface.

The implementation of quantum network made up of multiple nodes and channels needs to take advantage of hybrid quantum systems. So far, in the hybrid ferromagnet-superconductor quantum system, the establishment of the remote effective interactions based on the virtual photons exchange mediated by the microwave cavity mode has been experimentally confirmed, providing a physical basis for the implementation of the remote signal transfer from one node to another. In this work, we put forward a magnon-based hybrid quantum system consisting of two macroscopic spin subsystems [i.e., millimeter-diameter ferromagnetic yttrium-iron-garnet (YIG) spheres] and one transmon-type superconducting qubit, and show that the mechanism of the cavity-mediated remote magnon-mode intertalk is feasible for achieving microwave signal transfer, simultaneously accompanied by a transition from Poissonian to sub-Poissonian statistics. We find that by tuning the typical system parameters properly, even if there is a mismatch in magnon-mode frequencies or dissipation rates between the two YIG spheres, the microwave information transfer from one YIG sphere to another is still robust, where the signal output through another YIG sphere exhibits pronounced antibunching. In addition, the proposed hybrid quantum system possesses a robustness window against the dissipation rates of both the qubit and the two Kittel modes. The analytical calculations and numerical simulations are conducted under experimentally accessible conditions, and the consistency of the results attained by these two methods makes our research more credible. Physically, we notice that two conversion channels are opened. One channel comes from the linear coupling. The other is based on the nonlinear interaction, which also is the underlying mechanism responsible for nonclassical sub-Poissonian signal output.

Here it is shown that the exciton interactions within organic dye aggregates, as modeled by the Frenkel Hamiltonian, enable the construction of an on-off switchable exciton gate. In this construction, a single exciton residing on a controlling gate molecule may pass or inhibit the ballistic propagation of an exciton in a proximal gate channel consisting of an array of dye molecules. High on-off ratios in excess of ${10}^2$ can be achieved through the use of static difference dipole-dipole interactions between the gate and the gate channel which effectively creates a switchable Bragg grating. The gate channel and controlling gate molecule exhibit entanglement with the quantum-mechanical superposition of the presence and absence of exciton occupation on the gate molecule.

We explore the formation of one-dimensional two-component quantum droplets with intercomponent particle imbalance using an ab initio many-body method. It is shown that for moderate particle imbalance each component maintains its droplet flat-top or Gaussian-type character depending on the intercomponent attraction. Importantly, large particle imbalance leads to a flat-top shape of the majority component with the minority exhibiting spatially localized configurations. The latter imprint modulations on the majority component which become more pronounced for increasing interspecies attraction. The same holds for larger mass or increasing repulsion of the minority species. Such structural transitions are also evident in the underlying two-body correlation functions. To interpret the origin and characteristics of these droplet states we derive an effective model based on the established Lee-Huang-Yang theory providing adequate qualitative analytical predictions even away from its expected parametric region of validity. In contrast, the droplet character is found to vanish in the presence of fermionic minority atoms. Our results pave the way for unveiling complex droplet phases of matter.

The preparation of mechanical quadrature-squeezed states holds significant importance in cavity optomechanics because the squeezed states have extensive applications in understanding fundamental quantum mechanics and exploiting modern quantum technology. Here, we propose a reliable scheme for generating mechanical quadrature squeezing in a typical cavity optomechanical system via seeking optimal cavity-field driving pulses using the gradient-descent algorithm. We realize strong quadrature squeezing in a mechanical resonator that exceeds the 3-dB steady-state limit, even with a thermal phonon occupancy of 100. Furthermore, the mechanical squeezing can be ultrarapidly created within one mechanical oscillation period. We also obtain the optimal pulsed drivings associated with the created mechanical squeezings and analyze the mechanism for mechanical squeezing generation. This paper will promote the application of optimal quantum control in quantum optics and quantum information science.

Asymmetric response is essential to form a nonlinearity-based nonreciprocal device. Here, we studied the asymmetric modal coupling in a passive resonator driven by the nonconservative coupling add-drop filter (NCC-ADF). When light is incident from either port, the proposed configuration can selectively excite supermodes and realize an asymmetric stored optical energy in the passive resonators. Such asymmetry can be tuned on demand by varying the amplitude and phase delay of the mirror system. Furthermore, by introducing the thermal-optic nonlinearity effect in the proposed configuration, an optical isolator with low-power and broadband nonreciprocal optical transmission can be realized. The linear and nonlinear mode dynamics in the NCC-ADF configuration with asymmetric modal couplings were effectively described through a temporal coupled mode theory. The theoretical result will find potential application in on-chip integrated isolators as well as microcavity-based applications.

We propose a scheme to achieve the simultaneous nonreciprocal photon blockade of two microring resonators in an all-optical system without any rotating parts. By unidirectionally parametrically pumping a ${\chi }^{\left(2\right)}$-nonlinear resonator with a classical coherent field, the counterclockwise mode in the resonator is exposed to the parametric amplification process when a forward signal field is input in another resonator, but not the case for a backward signal field. This leads to different quantum interference effects among distinct excitation paths for two optical modes, which is the essential reason for simultaneous nonreciprocal photon blockade. We analytically give the optimal parameter conditions to achieve simultaneous strong photon blockade with the parametric amplification. Furthermore, the nonreciprocity is simultaneously enhanced through tuning the amplitude of input signal. Our work provides an avenue to realize simultaneous nonreciprocal single-photon devices without moving parts and may have potential applications in many-body quantum information processing and quantum communication.

An approach for studying atom-radiation interaction has been developed, associating quantum operators with stochastic variables governed by discrete Heisenberg equations. This framework models general multilevel atomic systems using the paraxial approximation in both single- and multipass configurations. Simulation results for x-ray laser oscillators with parameters of interest are presented. The stochastic model is efficient to solve, as the required computational resources scale linearly with the number of emitters, and it may be applicable to various other quantum systems.