We suggest a scheme for generating multimode squeezed states for the boson sampling implementation. The idea is to replace a commonly used linear interferometer by a multimode resonator which contains a passive optical element consisting of two-level Bose atoms dispersively interacting with photons and self-generating a squeezed compound state of both bosons—photons and atoms. The suggested scheme does not need (1) on-demand external sources of photons in squeezed or Fock quantum states or (2) numerous interchannel couplers which introduce phase noise and losses that prevent scaling up the system and achieving quantum advantage. The idea is illustrated by a setup based on a Bose-Einstein-condensed gas placed inside a multimode resonator, one of whose optical modes is in the classical coherent regime. The joint probability distribution of photon and/or noncondensed atom numbers is calculated via a matrix hafnian that, for certain parameters of the system, is hardly to be effectively calculated by classical computers. Such experiments are at reach via existing cavity-QED and cold-gas technology.

Standard communication systems have transmission spectra that characterize their ability to perform frequency multiplexing over a finite bandwidth. Realistic quantum signals in quantum communication systems like transducers are inherently limited in time due to intrinsic decoherence and finite latency, which hinders the direct implementation of frequency-multiplexed encoding. We investigate quantum channel capacities for bandwidth-and-time-limited channels to establish the optimal communication strategy in a realistic setting. For pure-loss bosonic channels, we derive analytical solutions of the optimal encoding and decoding modes for Lorentzian and box transmission spectra, along with numerical solutions for various other transmissions. Our findings reveal a general feature of sequential activation of quantum channels as the input signal duration increases, as well as the existence of optimal signal length for scenarios where only a limited number of channels are in use.

In a recent publication [Dalen and Selstø, Phys. Rev. A 111, 033116 (2025)], it was demonstrated how converged photoelectron spectra could be determined using a complex absorbing potential on a truncated numerical domain considerably smaller than the extension of the dynamical wave function. That approach required simulation until virtually all unbound parts of the wave function were absorbed, far beyond the duration of the interaction with the external field. In this work we formulate the method in a semianalytical manner which allows us to extrapolate to infinite times after the interaction with the external field. In addition to obtaining photoelectron spectra for hydrogen differential in energy and ejection angle, we also demonstrate how—and when—the absorber may be seen as a detector, distorting the angular distributions when the detector is placed in the extreme vicinity of the atom.

We present a ($1+1$)-dimensional quantum model designed to describe nonsequential double ionization (NSDI) in homonuclear diatomic molecules exposed to strong linearly polarized laser fields. Extending the restricted-geometry framework previously developed for atomic systems by Eckhardt and Sacha, our approach captures key features of NSDI, including the characteristic knee structure in double ionization yields. Despite its simplifying assumptions, the model shows good agreement with experimental data and proves particularly suitable for systems with $\sigma$-type orbital symmetry. It offers a computationally efficient tool for exploring multielectron dynamics in molecular systems.

We observe experimental results that support photoionization-assisted resonant high-order harmonics from laser-ablated tin. Experiments were performed using pump lasers with wavelengths of 800, 1750, and 1780 nm. At 800 nm laser wavelength, we observe the splitting of the 17th-order harmonic into multiple components due to the presence of strong Sn iii transitions at 26.83 eV and 27.14 eV, in addition to the well-known strong Sn ii transition at 26.27 eV that generates single-harmonic enhancement as per the four-step model. For driving laser wavelengths of 1750 nm and 1780 nm, we observe multiple harmonic enhancements between 26 eV and 30 eV, where several strong transitions of Sn iii are identified. Despite the appearance of harmonics due to Sn iii transitions, the harmonic cutoff is similar to the values observed in previous studies in which Sn ii was the main harmonic emitter. These observations reveal that Sn iii does not directly participate in the harmonic generation process through the tunnel ionization of its valence shell electron, but rather appears in the harmonic spectra through the photoionization of the autoionization state of Sn ii.

We theoretically explore the dynamics of spatial solitons in nonlinear or interacting bosonic topological insulators. We employ a time-reversal broken Lieb-lattice analog of a Chern insulator and find that in the presence of a saturable nonlinearity, stable solitons bifurcate from a band of nonzero Chern number into the topological band gap with vortexlike structure on a sublattice. We numerically demonstrate the existence stable vortex solitons for a range of parameters and that the lattice soliton dynamics is subject to the anomalous velocity associated with large Berry curvature at the topological Lieb band edge. The features of the vortex solitons are well described by an underlying continuum Dirac model. We further show a different kind of interaction: When these topological solitons bounce off the edge of a finite structure, they create chiral edge states, and this give rise to an anomalous reflection of the soliton from the boundary.

Coherent perfect absorption (CPA) arises from the destructive interference of all scattering amplitudes, enabling complete light absorption within a lossy medium and suppressing both reflection and transmission channels. We propose to create a CPA in a cavity-magnon optomechanical system, where the system under study is comprised of an optomechanical cavity coupled to a yttrium iron garnet sphere. Our investigation reveals that the interaction between the cavity and the magnon modes plays a central role in achieving and controlling CPA in this hybrid system. Furthermore, we also find that perfect photon absorption can coexist with optical bistability under specific input intensity conditions when a coupling exists between the cavity and the mechanical mode.

Quantum entanglement stands as an intriguing and pivotal phenomenon in quantum mechanics, forming the cornerstone for the realization of technologies transcending classical boundaries and enabling the practical deployment of diverse quantum devices. Here, we propose a method to manipulate both the pairwise entanglement among exciton-photon, exciton-phonon, and photon-phonon modes, and the tripartite entanglement involving exciton, photon, and phonon modes, within a hybrid exciton-optomechanics system, utilizing two pump lasers propagating in different directions. We find that all three distinct types of bipartite quantum entanglement and the tripartite entanglement can be effectively controlled and even enhanced along with improved robustness against environmental thermal noise by properly adjusting the phase difference between the two pump lasers. Our findings open up an easily accessible method for manipulating and protecting quantum entanglement, which is crucial in a wide range of practical applications requiring purely quantum resources, such as noise-tolerant quantum processing and quantum precision measurements.

Processing in memory (PIM) has received significant attention due to its high efficiency, low latency, and parallelism. In optical computation, coherent memory is a crucial infrastructure for PIM frameworks. This study presents an all-optical convolution experiment conducted within computational storage based on a cold atomic ensemble. By exploiting the light-atom phase transfer facilitated by the electromagnetically induced transparency, we demonstrated spiral phase contrast processing of photon images in a memory, resulting in the edge enhancement of retrieved images recorded using time-correlated photon imaging. In particular, adopting state-of-the-art atomic techniques provides a coherent memory lifetime exceeding 320 $\mu \text{s}$ for PIM operations. Our results highlight the significant potential of cold atomic ensembles as computational storage for developing all-optical PIM systems.

Recently, the concept of universal photon blockade, which unifies the physical mechanisms of conventional and unconventional photon blockade, was proposed based on a two-photon Jaynes-Cummings model [Y.-H. Zhou, T. Liu, Q.-P. Su, X.-Y. Zhang, Q.-C. Wu, D.-X. Chen, Z.-C. Shi, H. Z. Shen, and C.-P. Yang, Phys. Rev. Lett. 134, 183601 (2025)]. In this paper, we introduce an approach to studying universal photon blockade by directly integrating the conditions for conventional and unconventional photon blockades. From a theoretical perspective, this approach can address the key question of “in which systems universal photon blockade can be realized” and establish a more intuitive analytical framework for understanding the relationships among conventional, unconventional, and universal photon blockades. We validate this approach by investigating universal photon blockade in a system of two coupled cavities with Kerr nonlinearities, and we find excellent agreement between the derived optimal conditions and precise numerical simulations. Our results establish a pathway for predicting universal photon blockade and hold promising potential for applications in generating antibunched photons.

We present a unified quantum open system framework for lossy plasmonic cavities, treating coherent dynamics, relaxation, dephasing, and irreversible absorption on an equal footing. The Dyson equation for the cavity photon propagator in the random-phase approximation yields a complex self-energy $\mathcal{S}\left(\omega \right)$ that accounts for both the renormalization and damping of hybrid plasmon-photon modes. It shows that increasing losses can drive a crossover from resolvable normal-mode splitting to a regime without resolved splitting, when the damping becomes comparable to or larger than the coherent hybridization scale. Tracing out the environment yields a Liouvillian for the upper polaritons (UPs) and lower polaritons (LPs) with leakage $\mathrm{\Gamma }=-2\mathrm{Im}\mathcal{S}\left(\omega \right)$, internal UP $\leftrightarrow$ LP scattering, and dephasing. Closed-form dynamics for populations and interbranch coherence provide analytic steady-state values, line shapes, and UP-LP quench rates, valid at low polariton density and in the ultrastrong-coupling regime. The theory is directly applicable to spectra, time-domain probes, and dissipation engineering in plasmonic and nanophotonic cavities.

We investigate the photon statistics of light emitted from a system of collectively interacting dipoles in the low-intensity regime, incorporating double-excitation states to capture beyond-single-excitation effects. By analyzing the eigenstates of the double-excitation manifold, we establish their connection to the accessible single-excitation eigenmodes and investigate the role of decay rates in shaping the zero-time-delay photon correlation function $g^{\left(2\right)}(\tau =0)$ under different detection schemes. The photon emission statistics can be arbitrarily controlled by interfering two beams of light that selectively address orthogonal eigenmodes. This can act as a tunable nonlinearity that enables both enhancement or suppression of two-photon emission.

The no-broadcasting theorem is a fundamental result in quantum information theory. It guarantees that a class of attacks on quantum protocols, based on eavesdropping and indiscriminate copying of quantum information, are impossible. Due to its fundamental importance, it is natural to ask whether it is an intrinsic quantum property or whether it also holds for a broader class of nonclassical theories. To address this question, one could use the framework of correlation scenarios. Under this standpoint, Joshi, Grudka, and the Horodeckis conjectured that one cannot locally broadcast nonlocal behaviors. In this paper, we prove their conjecture based on the monotonicity of the relative entropy for behaviors. Additionally, following a similar reasoning, we obtain an analogous no-go theorem for steerable assemblages.

We present a multitimescale quantum averaging theory (QAT), a unitarity-preserving generalized Floquet framework for analytically modeling periodically and almost periodically driven quantum systems across multiple timescales. By integrating the Magnus expansion with the method of averaging on multiple scales, QAT captures the effects of both far-detuned and near-resonant interactions on system dynamics. The framework yields an effective Hamiltonian description while retaining fast oscillatory effects within a separate dynamical phase operator, ensuring accuracy across a wide range of driving regimes. We demonstrate the rapid convergence of QAT results toward exact numerical solutions in both detuning regimes for touchstone problems in quantum information science.

Starting from a generalization of Weyl's relations in finite dimension $N$, we show that the Heisenberg commutation relations can be satisfied in a specific ($N-1$)-dimensional subspace and display a linear map for projecting operators to this subspace. This setup is used to construct a hierarchy of parameter-dependent commuting matrices in $N$ dimensions. This family of commuting matrices is then related to type-1 matrices representing quantum integrable models. The commuting matrices find an interesting application in quantum computation, specifically in Grover's database search problem. Each member of the hierarchy serves as a candidate Hamiltonian for quantum adiabatic evolution and, in some cases, achieves higher fidelity than standard choices, thus offering improved performance.

Experimentally measured reduced density matrices (RDMs) often violate constraints that ensure they represent $N$-electron states—known as $N$-representability conditions—because of statistical and hardware noise. We present a correlated purification framework based on semidefinite programming to restore the accuracy of a noisy, unphysical two-electron RDM (2-RDM). The method performs a bi-objective optimization that minimizes both the many-electron energy and the nuclear norm of the correction to the measured 2-RDM. The nuclear norm, often employed in matrix completion, promotes low-rank corrections, while the energy term acts as a regularization term that can improve the purity of the ground state. While the method is particularly effective for ground states, it can also be applied to excited and nonstationary states by decreasing the weight of the energy relative to the error norm. In an application to fermionic shadow tomography of large hydrogen chains, correlated purification yields substantial reductions in both energy and 2-RDM error, achieving chemical accuracy across dissociation curves. This framework provides a robust strategy for tomography in many-body quantum simulations.

According to Rayleigh's criterion, two incoherent emitters with a separation below the diffraction limit are not resolvable with a conventional fluorescence microscope. One method of superresolution microscopy (SRM) circumvents the diffraction-limited resolution by precisely estimating the position of spatiotemporally independent emitters. However, these methods of SRM techniques are not optimal for estimating the separation of two simultaneously excited emitters. Recently, a number of detection methods based on modal imaging have been developed to achieve the quantum Cramér-Rao lower bound (QCRB) to estimate the separations between two nearby emitters. The QCRB determines the minimum achievable precision for all possible detection methods. Current modal imaging techniques assume a scalar field generated from a point source, such as a distant source from an optical fiber or a pinhole. However, for fluorescently labeled samples, point emitters are single fluorophores that are modeled as dipole emitters and, in practice, are often freely rotating. Dipole radiation must be described by vectorial theory, and the assumption of a scalar field no longer holds. Here, we present a method to numerically calculate the QCRB for measuring the separation of two dipole emitters, incorporating the vectorial theory. Furthermore, we propose a near-quantum optimal detection scheme based on one of the modal imaging techniques, superlocalization by image inversion interferometry (SLIVER), for estimating the separation of two freely rotating dipoles. In the proposed method, we introduce a vortex wave plate before the SLIVER detection to separate the radial and azimuthal components of the dipole radiation. With numerical simulations, we demonstrated that our method achieves nondivergent precision at any separation between two dipole emitters. We investigated several practical effects relevant to experimental measurements in superresolution microscopy, including numerical aperture, detection bandwidth, number of estimation parameters, background, and misalignment on separation estimation. Our proposed measurement provides a near-quantum-limited detection scheme for measuring the separation of two freely rotating dipole emitters, such as fluorescently tagged molecules, which are commonly used in superresolution microscopy.

In superconducting quantum circuits, decoherence errors in qubits constitute a critical factor limiting quantum gate performance. To mitigate decoherence-induced gate infidelity, rapid implementation of quantum gates is essential. Here we propose a scheme for rapid controlled-$Z$ (CZ) gate implementation through energy-level engineering, which leverages Rabi oscillations between the $|11\rangle$ state and the noncomputational state in a tunable-coupler architecture. Numerical simulations achieved a 22-ns nonadiabatic CZ gate with fidelity greater than $99.99\%$. We further investigated the performance of the CZ gate in the presence of anharmonicity offsets. The results demonstrate that a high-fidelity CZ gate with an error rate below ${10}^{-4}$ remains achievable even with finite anharmonicity variations. Furthermore, the detrimental impact of spectator qubits in different quantum states on the fidelity of the CZ gate is effectively suppressed by incorporating a tunable coupler. This scheme exhibits potential for extending the circuit execution depth constrained by coherence time limitations.

Reaching fast and robust two-qubit gates with low infidelities has been an outstanding challenge for the long-term goal of useful quantum computers. Typically, optimizing the pulse shapes can minimize the gate infidelity and improve its robustness to certain types of errors; yet it remains incapable of speeding up the gate execution time, which is fundamentally restricted by the attainable Rabi frequency in a realistic setup. In this work, we develop a fast implementation of two-qubit controlled-$Z$ (cz) gates using an optimized ancillary drive to enhance the two-photon Rabi frequency between the ground and Rydberg states. This ancillary drive can work in an error-robustness framework without increasing the original gate infidelity in the absence of the drive. Considering the experimentally feasible parameters for ${}^{87}\mathrm{Rb}$ atoms, we demonstrate that the execution time required for such cz gates can be shortened by more than $30\%$ as compared to standard two-photon protocols, increasing the gate fidelity above 0.9954 by taking account of all relevant error sources. Our results reduce the high-power laser requirement and unlock the potential toward fast, high-fidelity quantum operations for large-scale quantum computation with neutral atoms.