A theoretical and numerical study of optical forces acting on a Rayleigh particle in a paraxial Gaussian light beam exhibiting regions of optical backflow is presented. Within the dipole approximation, the total optical force is decomposed into gradient, scattering, and spin-curl terms. Vector fields satisfying the exact paraxial Maxwell equations are employed to describe the structured light configuration responsible for two distinct mechanisms leading to backward optical forces. The first originates from the local reversal of the Poynting vector, which induces a negative longitudinal momentum flux, while the second arises from the spin-dependent component of the force associated with the spatial variation of the optical spin density. Analytical expressions and numerical simulations confirm that both mechanisms can produce backward motion of a Rayleigh particle under appropriate beam conditions. These results provide a unified physical picture of backward-directed optical forces in Gaussian beams and open possibilities for particle manipulation in structured light fields.

We describe the generation of correlated photon pairs by means of spontaneous parametric down-conversion of an optical pump in the form of a finite-energy Airy beam. The optical system function, which contributes to the propagation of the down-converted beam before being registered by the detectors, is computed. The spectral function is utilized to calculate the biphoton amplitude for finding the coincidence count of the inbound Airy photons in both far-field and near-field configurations. We report the reconstruction of the finite-energy Airy beam in the spatial correlation of the down-converted beams in a near-field scenario. In the far field, the coincidence counts resemble the probability density of the biphoton in momentum space, revealing a direct mapping of the anticorrelation of the biphoton momentum. By examining the spatial Schmidt modes, we also demonstrate that longer crystals have tighter real-space correlations, but higher-dimensional angular correlations, whereas shorter crystals have fewer modes in momentum space and broader multimode correlations in position space.

Collision models provide a simple and versatile setting to capture the dynamics of open quantum systems. The standard approach to thermalization in this setting involves an environment of independent and identically prepared thermal qubits, interacting sequentially for a finite duration $\mathrm{\Delta }t$ with the system. We compare this to a two-bath scenario in which collisional qubits are prepared in either their ground or excited states and the environment temperature is encoded in system-environment couplings. The system reaches the same thermal steady state for both settings, although even in this limit they describe fundamentally different physical processes, with the two-bath setup yielding a nonequilibrium state with finite heat currents. Non-Markovian dynamics arises when intraenvironment interactions in either setting are introduced. Here the system in the single-bath setup again reaches a steady state at the canonical temperature of the bath, but the nonequilibrium steady state of the two-bath setup tends to a different temperature due to the generation of strong system-environment and intraenvironment correlations. The two-bath setting is particularly suited to studying quantum trajectories, which are well defined also for the non-Markovian case. We showcase this with a trajectory analysis of the heat currents within a two-point measurement scheme. Finally, we consider how our results are impacted when the system-environment interaction leads to strict homogenization. Our results provide insights into the dynamics and thermodynamics of thermalization towards nonequilibrium steady states and the role of non-Markovian interactions.

Quantum state transfer, from one location to multiple different locations via the control of a quantum switch, is of fundamental interest in quantum physics. It has potential applications in networked quantum communication, information processing, and development of quantum technologies and quantum functional devices. Here we consider a circuit-QED system, which consists of an input microwave cavity, $n$ output microwave cavities, and an ($n+2$)-level superconducting (SC) qudit (acting as a multiplex switch). We show that arbitrary quantum states initially stored in the input cavity can be transferred to $n$ different output cavities when the SC-qudit switch is in different states. The operational time does not depend on the output-cavity number. Since the two auxiliary higher-energy levels of the qudit are almost not excited during the state transfer, decoherence from these two levels is greatly suppressed. The state transfer can be realized deterministically because no state measurement is needed. We further numerically analyze the experimental feasibility of transferring arbitrary states of a photonic qubit from one input cavity to two output cavities via the control of a SC-flux-ququart switch (a four-level system). This proposal may be extended to accomplish the same task in other physical systems, where the switch is a multilevel artificial atom of different types and each cavity is a microwave or optical cavity.

Recently, a toolkit of highly symmetric techniques employing matrix inequalities and positive maps has been developed to detect entanglement in various ways. Here we concisely review these methods providing a unified framework, and expand them to a family of positive maps with further detection capabilities. In the simplest case, we generalize the reduction map to detect more generic states using both multiple copies and local filters. Through the Choi-Jamiołkowski isomorphism, this family of maps leads to a construction of multipartite entanglement witnesses. Discussions and examples are provided regarding the detection of states with local positive partial transposition and the use of multiple copies.

We report in situ measurements of the nonlocal two-body spatial correlation function $g^{\left(2\right)}\left(R\right)$ in an ultracold Bose gas with strong interactions using photoassociation of ultra-long-range Rydberg molecules (ULRRMs) as a spatially selective probe. This technique provides access to $g^{\left(2\right)}\left(R\right)$ on length scales from 60 to 180 nm, bridging the gap between short-range and long-range correlation measurements. The large $s$-wave scattering length of ${}^{86}\mathrm{Sr}$ ($a=811a_0$) enables exploration of the universal regime where $g^{\left(2\right)}\left(R\right)$ is governed solely by two-body interactions. Comparison with a weakly interacting isotope, ${}^{84}\mathrm{Sr}$, highlights interaction-induced suppression of pair correlations. The measured correlation functions agree quantitatively with ab initio calculations based on the two-body reduced density matrix, without adjustable parameters. Our results establish Rydberg molecular photoassociation as a powerful tool for probing nonlocal correlations in situ in strongly interacting quantum gases.

Coherent superpositions of electronic states generate rapid charge migration and it is essential to pursue ultralong-lived charge migration in molecules. Here, we design a polarized pulse train to enhance and maintain charge migration in ionized iodoacetylene (${\mathrm{HCCI}}^{+}$). By sequentially tuning the carrier-envelope phases of these short pulses, we achieve equal populations of the ground and first excited states while maintaining high nuclear overlap. Compared to the field-free scenario, both the amplitude and duration of charge migration are improved. This approach offers a robust framework for electronic coherence control and can be readily extended to more complex molecular systems.

We present an experimental, numerical, and analytical study of strontium magneto-optical-trap (MOT) loading from a cold atomic beam in a configuration optimized for high numerical aperture optical tweezers. Our approach orients the beam flow along the MOT symmetry axis to reduce the experimental complexity and maximize the overall optical access into the scientific region of study. We use a moving molasses technique to enable this configuration and show that its performance depends critically on metastable-state shelving (to $5s5p{}^{3}P_2$) during the atom transfer to the three-dimensional (3D) MOT. Furthermore, we find that the parameters for optimal transfer efficiency are bounded by dark-state loss (to $5s5p{}^{3}P_0$) in the trap region where repumping is present. These observations are verified to a great degree of accuracy using both our developed analytical and numerical models. The corresponding 3D simulation tool is used to perform a comprehensive study of the trap loading dynamics, beginning at the oven exit and ending at the 3D MOT, demonstrating its effectiveness in optimizing an effusive oven experiment.

The ability to precisely control and predict the evolution of quantum states is a fundamental requirement for advancing quantum technologies. Here, we develop tunable atomic routing protocols based on an integrable model of dipolar bosons confined in a four-well potential with a star-shaped configuration. By adjusting the system parameters, we identify a harmonic dynamical regime of the atomic population that can be treated analytically, providing a complete description of the system's behavior for precise manipulation. We demonstrate three independent modes of control over the atomic population dynamics under the action of an external field: frequency tuning via variation in the field intensity or in the initial occupation of the central well, directional switching via spatial displacement of the field, and amplitude modulation by varying its duration. These modes operate under two distinct configurations: one source and two drains, and, in reverse order, two sources and one drain. These cases emulate an atomic 1:2 demultiplexer and 2:1 multiplexer, respectively. Our results may contribute to the development of control mechanisms in the design of quantum devices.

Atom interferometers require both high efficiency and robust performance in their mirror pulses under experimental inhomogeneities. In this work, we demonstrated that a quantum optimal-control-designed mirror pulse significantly enhances interferometer performance by using an adaptive sliced structure. Using gradient ascent pulse engineering (GRAPE), an optimized mirror pulse for a Mach-Zehnder light-pulse atom interferometer was designed by discretizing the control into nonuniform phase slices. This design broadened the tolerence to experimentally relevant variations in detuning $[-{\mathrm{\Omega }}_0,{\mathrm{\Omega }}_0]$ and Rabi frequency $[0.1\times {\mathrm{\Omega }}_0,1.9\times {\mathrm{\Omega }}_0]$ (${\mathrm{\Omega }}_0=2\pi \times 25\mathrm{kHz}$), while maintaining high transfer efficiency even when the response-time delays up to 1.6 $\mu \mathrm{s}$. The optimized pulse was found to be robust to coupling inhomogeneity and velocity spread, offering a significant improvement in robustness over the conventional pulse. The adaptive pulse slicing method provides a minimalist strategy that reduces experimental complexity while enhancing robustness and scalability, offering an innovative scheme for quantum optimal control in high-precision atom interferometry.

We introduce and benchmark an improved algorithm for complex Langevin simulations of bosonic coherent state path integrals. Our approach utilizes a Strang splitting of the imaginary-time propagator rather than the conventional linear-order Taylor expansion, allowing us to construct an action that incorporates higher-order terms at negligible computational cost. The resulting algorithm enjoys guaranteed linear stability independent of the imaginary-time discretization, enabling more resource-efficient simulations. We demonstrate this improved performance for single-species bosons and for two-component bosons with Rashba spin-orbit coupling.

The precise, nondestructive quantification of local surface curvature is paramount for advancements in precision manufacturing, biomedical engineering, and industrial quality control. However, conventional techniques, including contact profilometry and optical interferometry, are constrained by potential surface damage, limited adaptability to complex geometries, and resolution trade-offs. To address these limitations, we introduce and experimentally demonstrate a noncontact spherometer based on an optical computing metasurface, enabling high-precision local curvature metrology at the micrometer level. This modality integrates all-optical object recognition for edge detection of intensity objects with quantitative phase imaging for the three-dimensional reconstruction of phase objects. Experimental validation on calibrated targets, including a standard steel sphere and a convex lens, demonstrates that the experiment exhibits high-precision characteristics. This work establishes metasurface-based optical computing as a versatile and robust platform for high-precision metrology, opening new avenues for in situ surface characterization across multiple disciplines.

We show that the distance between two qubits coupled to a structured reservoir acts as a single geometric control that can store, revive, or suppress Bell nonlocality. In a mirror-terminated guide, quantum correlations lost to the bath return at discrete recurrence times, turning a product state into a Bell-violating one without any entangling drive (only local basis rotations and/or readout). In the continuum limit, we derive closed-form criteria for the emergence of nonlocality from backflow, and introduce a Bell-based analog of the Breuer-Laine-Piilo measure to quantify this effect. We also show how subwavelength displacements away from a decoherence-free node quadratically reduce the lifetime of a dark state or bright state, enabling highly sensitive interferometric detection. All results rely on analytically solvable models and are compatible with current superconducting and nanophotonic platforms, offering a practical route to passive, geometry-controlled non-Markovian devices.

The static Stark effect was investigated at very high electric fields of up to 690 kV/cm in the near-infrared lines between the levels of the $2s^{2}2p^2(3s,3p)$ configurations in the 742.36–939.28-nm spectral range, allowing us to obtain values of the differences of the scalar polarizabilities $\mathrm{\Delta }{\alpha }_0$. For the investigated lines, values were found to be very small, ranging from 30 to $200\mathrm{kHz}/{(\mathrm{kV}/\mathrm{cm})}^2$, while the tensor polarizabilities ${\alpha }_2$, associated with the splitting of the $\mathrm{\Delta }M$ line components, were found to be very small and not within the capabilities of the current experiment. Based on the most recent available atomic data, the polarizabilities ${\alpha }_0$ and ${\alpha }_2$ have been calculated for the investigated excited states, where significant differences were found with the current experiment. Values that were significantly more precise were obtained by fitting the polarizibility values of each level separately to match the values of the polarizibility differences observed in the experiment. For the experimentally investigated excited states of the $2s^{2}2p^{2}3s$ configuration, the scalar polarizabilities ${\alpha }_0$ were found to be in a range of 77 to $108\mathrm{kHz}/{(\mathrm{kV}/\mathrm{cm})}^2$, and 108 to $308\mathrm{kHz}/{(\mathrm{kV}/\mathrm{cm})}^2$ for the states of the $2s^{2}2p^{2}3p$ configuration. Values for the excited states are one and two orders of magnitude higher than those for the ground state. With the help of these data, predictions of Stark shifts for the remaining lines between the levels of both configurations have been made.

A time delay for the open-shell Na $3s$ photoemission process is investigated using the Breit-Pauli $R$-matrix methodology. The results show dramatic variations with the energy and angle in the vicinity of the Cooper minimum owing to both relativistic dynamics and angular momentum geometry effects.

We report on the observation, characterization, and control of the electron dynamics in ionized argon atoms. We utilize an intense midinfrared (MIR) pulse to create a coherent superposition of the spin-orbit split ground state of the ion. A weak extreme ultraviolet (XUV) pulse then probes the hole oscillation through time-resolved transient absorption spectroscopy. We investigated several $3p$ to $nd$ transitions accessible with our XUV high harmonics, which show a 23 fs beat corresponding to the energy separation between the initially populated states. The experimental attosecond transient absorption signals for different pathways were simulated using detailed time-dependent Schrödinger equation  simulations and perturbative analytic calculations. The analysis of phase relations between the oscillations reveals important information about transition dipole moments in the system. In addition, we employed another strong MIR pulse to achieve transient control over the absorption by inducing Stark shifts of the states without affecting the electronic coherences.

This paper presents an experimental study of microwave single-photon transitions that are magnetic-field-insensitive in degenerate Fermi gases of ${}^{40}\mathrm{K}$. This contrasts with microwave single-photon clock transitions for 0–0 magnetic-field-insensitive states and two-photon clock transitions for non-0–0 magnetic-field-insensitive states in bosonic alkali-metal atoms. We show that there are two sets of special transitions between two different hyperfine ground states ($|F=9/2,m_F=1/2\rangle \iff |7/2,-1/2\rangle$ and $|9/2,-1/2\rangle \iff |7/2,1/2\rangle$), whose microwave single-photon transition frequency is insensitive to low magnetic fields, as the first-order Zeeman shift is almost completely canceled. By using the microwave spectrum and Ramsey interference fringes, we demonstrate the long-time stability of the coherent transition under magnetic field fluctuations. These magnetic-field-insensitive microwave hyperfine transitions in ultracold ${}^{40}\mathrm{K}$ Fermi gases offer promising applications in quantum information and precision measurements.

We propose a discrete-space representation of a one-dimensional zero-range odd-parity pseudopotential. The proposed representation is validated by applying it to the analytically solvable case of two fermions in a harmonic trap and successfully recovering the exact energy spectrum and eigenfunctions. Furthermore, we use the square-well and modified Pöschl-Teller potentials as finite-range representations of the odd-parity interaction and study their convergence to the contact interaction when the range tends to zero. Finally, we perform natural orbital analysis and compute the eigenvalues of the one-body density matrix for different particle numbers, examining their dependence on the one-dimensional scattering length and identifying distinct physical regimes.

Non-Hermitian photonics provides a fertile platform for exploring phenomena with no Hermitian counterparts, including the non-Hermitian skin effect and exceptional points, with direct relevance for integrated photonic technologies. In this work, we investigate the properties of non-Hermitian second-order topological phases by constructing a photonic kagome crystal with balanced gain and loss, and reveal the interplay between higher-order topology and the non-Hermitian skin effect. We demonstrate that non-Hermiticity not only lifts the degeneracy of the topological corner modes but also drives bulk states to accumulate at the corners, giving rise to a bipolar non-Hermitian skin effect. By defining the point-gap topology, we uncover the fundamental topological origin of the non-Hermitian skin effect. More interestingly, the non-Hermitian skin effect induces a fundamental breakdown of the conventional bulk-boundary correspondence based on the Bloch band theory. Our findings establish a general framework for non-Hermitian higher-order photonic systems and open avenues toward tailorable topological photonic devices exploiting non-Hermitian enhanced localization.