We demonstrate a method for determining the radius of micron-sized particles trapped by a vortex laser beam. The technique is based on measuring the rotation experienced by the center of mass of a microsphere that is laterally displaced by a Stokes drag force to an off-axis equilibrium position. The rotation results from an optical torque pointing along the direction opposite to the vortex beam angular momentum. We fit the rotation angle data for different Laguerre-Gaussian modes taking the radius as a fitting parameter in the Mie-Debye theory of optical tweezers. We also demonstrate how the setup described here can be employed to characterize the astigmatism and spherical aberration introduced by the experimental setup, while at the same time determining the height of a microsphere with respect to the bottom of the solution within which it is contained.

The problem of the interaction of light waves with charged particles becomes increasingly complex starting with the case of plane waves, where the analytical solution is well known, to more natural, though more complicated situations which include focused or structured laser beams. Internal structure may introduce a new degree of freedom and qualitatively change the dynamics of interacting particles. For certain conditions, namely, for the dilute plasma, a description of single-particle dynamics in the focused structured laser beams is the first step and may serve as a good approximation to understand the global plasma response. Moreover, the general problem of integrability in complex systems starts from a consideration of the integrals of motion for a single particle. The primary goal of this work is an understanding of the physics of the orbital angular momentum (OAM) absorption by a single particle in a focused structured light. A theoretical model of the process, including solutions of Maxwell equations with the required accuracy and a high-order perturbative approach to electron motion in external electromagnetic fields, is developed and its predictions are examined with numerical simulations for several exemplary electromagnetic field configurations. In particular, it was found that for the particles which are initially distributed with the azimuthal symmetry around the beam propagation direction, the transferred OAM has a smallness of the fourth order of the applied field amplitude and requires an accurate consideration of the temporal laser pulse envelope.

Nonreciprocal devices are crucial components in optical information processing and chiral quantum networks. By investigating the topological property and the nonreciprocity in a one-dimensional, non-Hermitian microtoroid cavities array, we find that non-Hermitian topological phase transition periodically occurs, and the associated periodic edge-cavity nonreciprocity emerges and peaks at the single-cavity exceptional points (EPs) when the array of cavities is in the topologically nontrivial phase. This nonreciprocity is associated with the topologically protected chiral-mode excitation. It has practical applications in both classical and quantum nonreciprocal devices, such as optical isolators and nonreciprocal optomechanical entanglement devices. These nonreciprocities are topologically protected, thus are robust to the disorder of system parameters. Our work offers an alternative approach to generate periodic single-cavity nonreciprocity with non-Hermitian topological effect, and fundamentally advance the fields of topological physics and nonreciprocity optics.

The energy extraction from quantum sources is a key task to develop new quantum devices such as quantum batteries (QB). In this context, one of the main figures of merit is the ergotropy, which measures the maximal amount of energy (as work) that can be extracted from the quantum source by means of unitary operations. One of the main issues to fully extract energy from the quantum source is the assumption that any unitary operation can be done on the system. This assumption, in general, fails in practice since the operations that can be done are limited and depend on the quantum hardware (experimental platform) one has available. In this work, we propose an approach to optimize the extractable energy inspired by the variational quantum eigensolver (VQE) algorithm. In this approach, we explicitly take into account a limited set of unitaries by using the hardware efficient ansatz (HEA) class of parameterized quantum circuits. As a QB we use an one-dimensional spin chain described by a family of paradigmatic first neighbor hamiltonians such as the $XXX$, $XXZ$, $XYZ$, $XX$, $XY$, and transverse Ising models. By building our parameterized quantum circuits assuming that different types of connectivity may be available depending on the quantum hardware, we numerically compare the efficiency of work extraction for each model. Our results show that the best efficiency is generally obtained with quantum circuits that have connectivity between first neighbor spins.

Self-testing protocols refer to novel device-independent certification schemes wherein the devices are uncharacterized and the dimension of the system remains unspecified. The optimal quantum violation of Bell's inequality facilitates such self-testing. In this work we put forth a protocol for self-testing of noisy quantum instruments, specifically, the unsharpness parameter of smeared projective measurements in any arbitrary dimension. Our protocol hinges on the sequential quantum violations of a bipartite Bell-type preparation noncontextual inequality, involving three measurement settings per party. First, we demonstrate that at most three sequential independent Bobs manifest simultaneous preparation contextuality with a single Alice through the violation of this inequality. Subsequently, we show that the suboptimal sequential quantum violations of the noncontextual inequality form an optimal set, eventually enabling the self-testing of a shared state, local measurements, and unsharpness parameters of one party. Notably, we derive the optimal set of quantum violations without specifying the dimension of the quantum system, thereby circumventing the constraint that may arise due to Naimark's theorem. Furthermore, we extend our investigation to quantify the degree of incompatible measurements pertaining to the sequential observers, exploring how variations in the degree of incompatibility impact the values of unsharp parameters necessary for sequential quantum violation.

Recently, the phase-of-phase (POP) attoclock scheme [reported in Nature Photon. 15, 765 (2021)] has been used to investigate the tunneling dynamics of krypton atoms, encompassing the electron sub-barrier phase and amplitude. However, the impact of initial atomic orbitals on the POP attoclock spectroscopy remains largely unexplored. Here, we scrutinize the influence of initial atomic orbitals on the contrast and phase spectra of POP attoclock using ${\mathrm{F}}^{-}$ ions as a specific example. It is found that the initial atomic orbital significantly impacts the contrast spectrum of the POP attoclock and the detachment time of low-energy electrons retrieved by the POP attoclock via the preexponential factor. Particularly for orbitals $p_{+}$ and $p_{-}$, the difference of retrieved detachment time can exceed 300 attoseconds at some emission angles. But for high-energy electrons, the detachment time is almost independent of the initial atomic orbital and can be accurately retrieved by the POP attoclock. This work underscores the profound influence of initial atomic orbitals on the measurement accuracy of the POP attoclock, and holds great significance for advancing POP attoclock spectroscopy.

Standard cavity cooling of atoms or dielectric particles is based on the action of dispersive optical forces in high-finesse cavities. We investigate here a complementary regime characterized by large cavity losses, resembling the standard Doppler cooling technique. For a single two-level emitter a modification of the cooling rate is obtained from the Purcell enhancement of spontaneous emission in the large cooperativity limit. This mechanism is aimed at cooling quantum emitters without closed transitions, which is the case for molecular systems, where the Purcell effect can mitigate the loss of population from the cooling cycle. We extend our analytical formulation to the many-particle case governed by small individual coupling, but exhibiting large collective coupling.

We demonstrate a left-right asymmetry control of the photoelectron angular distribution in multiphoton ionization of Li atoms by a bichromatic laser field. By delaying the fundamental (780 nm) and its second harmonic relative to each other in steps of 130 attoseconds, we can vary the relative phase between the two laser fields with subwavelength accuracy and thereby steer the ejected electrons. Good agreement is found between the measurements and calculations at the appropriate intensities of the two harmonics.

The photonic spin Hall effect (PSHE) with high efficiency is of significance for the application of spin photonic devices, but the spin-dependent separation induced by the refraction or reflection at the interface of the media is too tiny to be used in practice. In this paper, we realize a PSHE by designing off-axis polarization singularity in free space and reveal the relationship between controllable spin-orbit coupling and orbital angular momentum (OAM) spectra of the off-axis vector beam. The numerical simulations and experimental results show that the spin-dependent separated distance and the OAM spectra are manipulated by the embedded position and polarization order of polarization singularity, and the separating direction perpendicular to the off-axis direction of polarization singularity. Our work provides a feasible and simple path for manipulating spin photons toward information processing based on optical spintronics.

We present a time-dependent variational approach with the multiple-Davydov-${\text{D}}_2$ trial state to simulate the dynamics of light-matter systems when the field is initially in a coherent state with an arbitrary finite mean photon number. The variational approach captures not only the system dynamics but also the field dynamics and is applicable to a variety of quantum models of light-matter interaction such as the Jaynes-Cummings model, Rabi model, and Dicke model and is capable of tackling multimode quantized fields. With a comparison of the variational and semiclassical dynamics of both the system and field, we illustrate that the variational dynamics from the quantum models agrees with those from the corresponding semiclassical models as long as the mean number of photons is sufficiently large. Moreover, we illustrate that in the crossover between the quantum and semiclassical limits, the quantum corrections lead to the collapse of the oscillations in dynamics, which is absent in the semiclassical models. The variational approach provides a unified treatment of light-matter interaction from the quantum to the semiclassical limit.

We experimentally and theoretically investigate the ellipticity dependence of Rydberg state excitation (RSE) and ionization of Ar subject to strong laser fields. It is found that, at 800 nm, the ratio of RSE to ionization yields decreases monotonically with ellipticity for the intensities explored in this work, while, at 400 nm, the ratio decreases monotonically in the high-intensity regime but increases in the low-intensity regime. A dedicated semiclassical model where the influences of Coulomb potential and nonadiabatic effect have been considered can reproduce the experimental observations qualitatively at 800 nm and the high-intensity regime at 400 nm. However, in the low-intensity regime at 400 nm, our semiclassical model cannot reproduce the experimental measurements, indicating that the well-accepted semiclassical frustrated tunneling ionization mechanism is not valid any more for a Keldysh parameter significantly larger than unity. Our work provides a comprehensive understanding of the atomic RSE process and raises a challenge for the theoretical methods in the future.

We consider the emergence of edge states in a finite optical lattice and show that the boundaries of the lattice play a decisive role for their location in the corresponding energy spectrum. We introduce a simple parametrization of the boundaries of the optical lattice and demonstrate the existence of an optimal choice of the values of the parameters which leads to an approximate restoration of chiral symmetry. A crucial property of this optimization is the suppression of tunneling between next-nearest-neighboring wells of the lattice. This in turn allows the mapping of the optical lattice setup to a finite SSH model. The topological character of the emerging edge states is discussed.

The systematic error induced by inhomogeneous residual magnetic fields through the quadratic Zeeman effect is non-negligible in atom interferometers and must be precisely evaluated. We use a hyperfine-ground-state-exchange (HGSE) method to evaluate the systematic error due to the quadratic Zeeman effect in the long-baseline ${}^{85}\mathrm{Rb}\text{−}{}^{87}\mathrm{Rb}$ dual-species atom interferometer. We compare the HGSE method to two alternative evaluation methods used in the past, mapping the absolute magnetic field in the interference region and performing phase measurements at different bias fields, obtaining consistent results with an accuracy at the ${10}^{-11}$ level. In addition, we show that, unlike the other methods, the HGSE method can obtain the systematic error induced by the quadratic Zeeman effect in real time in case of slow drifts of either the ambient magnetic field or other systematic effects differential to the two hyperfine ground states. Using the HGSE method to suppress the quadratic Zeeman-effect-induced systematic error in long-baseline atom interferometer-based precision measurements could enable searches for new physics such as testing the equivalence principle.

In the context of quantum objectivity, a standard way to quantify the classicality of a state is via the mutual information between a system and different fractions of its environment. Many of the tools developed in the relevant literature to quantify quantum objectivity via quantum mutual information rely on the assumption that information about the system leaks symmetrically into its environment. In this work, we highlight the importance of taking this assumption into account, and in particular, we analyze how taking nonaveraged quantum mutual information as a quantifier of quantum objectivity can be severely misleading whenever information about the system is encoded into the environment in a nonhomogeneous way. On the other hand, the averaged mutual information always provides results with a clear operative interpretation.

Recurrence is an interesting property that describes whether the walker will eventually return to the origin on infinite lattices in classical random walks. Since measurement collapse affects the wave function of the walker, in the quantum case, there are two schemes for studying recurrence properties in quantum walks (QWs) depending on how the measurement process is described. One involves restarting after measurements, known as unmonitored measurements, while the other entails monitoring after each step, referred to as monitored measurements. In this paper, we utilize the dependence of recurrence probabilities on the coin parameter to construct biased-coin QWs on a line and investigate the recurrence properties of both schemes. Based on the bulk-optics framework and using a single-photon source, we experimentally demonstrate the distinct recurrence behaviors resulting from the different evolution processes of the walker in the two schemes. This work showcases diverse recurrence properties in single-particle QW systems, thereby enhancing our understanding of measurement-induced recurrence.

We use symmetric measurement operators to construct quantum channels that provide a further generalization of generalized Pauli channels. The resulting maps are bistochastic but, in general, no longer mixed unitary. We analyze their important properties, such as complete positivity and the ability to break quantum entanglement. In the main part, we consider the corresponding open quantum systems dynamics with time-local generators. From the divisibility properties of dynamical maps, we derive sufficient Markovianity and non-Markovianity conditions. As instructive examples, we present the generators of P-divisible generalized Pauli dynamical maps that allow for more negativity in the decoherence rates.

Recent advancements have expanded Hardy's nonlocality arguments into multisetting and multidimensional systems to enhance quantum correlations. In comparison with Hardy's nonlocality argument, Cabello's nonlocality argument (CNA) emerges as a superior choice for illustrating nonlocal features. An open question persists regarding the potential extension of CNA to arbitrary ($k, d$) scenarios. Here, we answer this question both in theory and experiment. Theoretically, by utilizing compatibility graphs, we construct a new logical framework for multisetting and multidimensional CNA, demonstrating an increase in the maximum successful probability with setting $k$ and dimension $d$. Experimentally, by employing controllable photonic orbital angular momentum entanglement, we exhibit nonlocality with an experimentally recorded probability of 20.29% in the (2, 4) scenario and 28.72% in the (6, 2) scenario. Our work showcases a sharper contradiction between quantum mechanics and classical theory, surpassing the bound limited by the original version.