Incompatibility and nonlocality are not only of foundational interest but also act as important resources for quantum information theory. In the Clauser-Horne-Shimony-Holt (CHSH) scenario, the incompatibility of a pair of observables is known to be equivalent to Bell nonlocality. Here, we investigate these notions in the context of qubit channels. The Bell-CHSH inequality has a greater perspective—compared to any genuine tripartite nonlocality scenario—while determining the interplay between nonlocality breaking qubit channels and incompatibility breaking qubit channels. In the Bell-CHSH scenario, we prove that if the conjugate of a channel is incompatibility breaking, then the channel is itself nonlocality breaking and vice versa. However, this equivalence is not straightforwardly generalized to multipartite systems, due to the absence of an equivalence relation between incompatibility and nonlocality in the multipartite scenario. We investigate this relation in the tripartite scenario by considering some well-known states like Greenberger-Horne-Zeilinger and $W$ states and using the notion of Mermin and Svetlichny nonlocality. By subjecting the parties in question to unital qubit channels, we identify the range of state and channel parameters for which incompatibility coexists with nonlocality. Further, we identify the set of unital qubit channels that is Mermin or Svetlichny nonlocality breaking irrespective of the input state.

We consider discrimination of geometrically uniform states, and analytically solve this problem for qubits. For qutrits, we obtain the exact solution to the optimal measurement when the defining unitary matrix for the geometrically uniform states is degenerate. We also show that if the unitary is nondegenerate then the optimal measurement for discriminating geometrically uniform qubits or qutrits can always be expressed as a rank-1 operator, which converts the original discrimination problem into an optimization of a sum of trigonometric functions with two real variables in the case of qutrits. Additionally, a geometrical interpretation of the optimal measurement for discriminating geometrically uniform qubits is given via the Bloch sphere representation.

Multipartite quantum correlation is important for both fundamental science and quantum information processing. Its enhancement is critical to improve the performance of physical systems. Therefore, it is of great practical significance to study the enhancement of multipartite quantum correlation. Here, we theoretically investigate a scheme for enhancing quadripartite quantum correlation by utilizing a phase-sensitive cascaded four-wave mixing (CFWM) process. We find that the intensity-difference squeezing (IDS) among the four output beams generated by the phase-insensitive CFWM process can be largely enhanced by introducing the phase-sensitive CFWM process. We also find that our phase-sensitive CFWM process can be used to generate intensity-sum squeezing (ISS), which cannot be generated by the phase-insensitive CFWM process. Moreover, we find that the maximum squeezing value of ISS is equal to that of IDS when the intensity gains of the three four-wave mixing processes are equal in the phase-sensitive cascaded scheme. In the end, we discuss the effects of the losses and the phase fluctuations on the squeezing values of our phase-sensitive CFWM process and the corresponding phase-insensitive CFWM process with the same intensity gains. It can be seen that the squeezing enhancement of our phase-sensitive CFWM process holds also in presence of the losses and the phase fluctuations. Our results pave the way for experimental implementation and may find applications in quantum metrology and quantum communication.

Realization of nonreciprocal transmission with low insertion loss and high contrast simultaneously is in great demand for one-way optical communication and information processing. Here we propose a generic approach to achieving perfect nonreciprocity that allows lossless unidirectional transmission by engineering energy losses. The loss of the intermediate mode induces a phase lag impinging on the indirect channel for energy transmission, which does not depend on the energy transmission direction. When the direct transmission channel coexists with the indirect lossy transmission channel, the dual-channel interference can be tuned to be destructive simultaneously for backward transmission from the rightmost mode to the leftmost mode, and for forward transmission from the leftmost mode to the intermediate mode. The former interference outcome corresponds to 100% nonreciprocity contrast, and the latter guarantees zero insertion loss for forward transmission. Additionally, our scheme also allows a nonreciprocity response over a wide bandwidth by increasing the losses while keeping perfect nonreciprocity at resonance. The robustness against loss indicates that our scheme is advantageous in the implementation of nonreciprocal optical devices with high performance.

While the theoretical studies in waveguide quantum electrodynamics predominate with single-photon and two-photon Fock-state (photon number states) input, the experiments are primarily carried out using a faint coherent light. We create a theoretical toolbox to compare and contrast linear and nonlinear light scattering by a two-level or a three-level emitter embedded in an open waveguide carrying Fock-state or coherent-state inputs. We particularly investigate light transport properties and the Kerr and cross-Kerr nonlinearities of the medium for the two types of inputs. A generalized description of the Kerr and cross-Kerr effect for different types of inputs is formulated using the first-order correlation function to compare the Kerr and cross-Kerr nonlinearity between two photons in these models.

Noise-induced decoherence is one of the main threats to large-scale quantum computation. In an attempt to assess the noise affecting a qubit, we go beyond the standard steady-state solution of the transmission through a qubit-coupled cavity in input-output theory by including dynamical noise in the description of the system. We solve the quantum Langevin equations exactly for a noise-free system and treat the noise as a perturbation. In the long-time limit the corrections may be written as a sum of convolutions of the noise power spectral density with an integration kernel that depends on external control parameters. Using the convolution theorem, we invert the corrections and obtain relations for the noise spectral density as an integral over measurable quantities. Additionally, we treat the noise exactly in the dispersive regime and again find that noise characteristics are imprinted in the long-time transmission in convolutions containing the power spectral density.

We explore the capabilities offered by attosecond extreme ultraviolet and x-ray pulses that can now be generated by free-electron lasers and high-order harmonic generation sources for probing photon-induced electron dynamics in molecules. We theoretically analyze how spatial and temporal dependence of charge migration in a pentacene molecule can be followed by means of time-resolved photoelectron microscopy on the attosecond timescale. Performing the analysis, we accurately take into account that an attosecond probe pulse leads to considerable spectral broadening. We demonstrate that the excited-state dynamics of a neutral pentacene molecule in real space map onto unique features of photoelectron momentum maps.

We analyze the change in the hyperradial Efimovian three-body potential as the two-body interaction is tuned from the broad to narrow Feshbach resonance regime. Here, it is known from both theory and experiment that the three-body dissociation scattering length $a_{-}$ shifts away from the universal value of $-9.7r_{\mathrm{vdW}}$, with $r_{\mathrm{vdW}}=\frac{1}{2}{(m{C}_6/{\hslash }^2)}^{1/4}$ the two-body van der Waals range. We model the three-body system using a separable two-body interaction that takes into account the full zero-energy behavior of the multichannel wave function. We find that the short-range repulsive barrier in the three-body potential characteristic for single-channel models remains universal for narrow resonances, while the change in the three-body parameter originates from a strong decrease in the potential depth. From an analysis of the underlying spin structure we further attribute this behavior to the dominance of the two-body interaction in the resonant channel compared to other nonresonant interactions.

In this work we propose epsilon-near-zero (ENZ) nanoparticles formed of metal and dielectric bilayers and employ the effective-medium approach for multilayered nanospheres to study their optical response. We obtain a passive tunable ENZ region by varying the radii of the proposed bilayer nanospheres, ranging from visible to near IR. In addition, we present the absorption and scattering cross section of ENZ nanoparticles using open-source transfer-matrix-based software (stratify). The proposed ENZ nanoparticle is envisioned to be experimentally realized using chemical synthesis techniques.

We present a scheme to create an all-optical tunable and lossless waveguide using a controllable coherent Raman process in an atomic rubidium vapor in an $\mathcal{N}$-type configuration. We employ a Gaussian Raman field and a Laguerre-Gaussian control field to imprint a high-contrast tunable waveguidelike feature inside the atomic medium. We numerically demonstrate that such a waveguide is able to guide arbitrary modes of a weak probe beam to several Rayleigh lengths without diffraction and absorption. Our results on an all-optical waveguide-based scheme may have potential applications in lossless image processing, high-contrast biomedical imaging, and image metrology.

In this paper we claim that a common underlying structure—a skeleton structure—is present behind discrete-time quantum walks (QWs) on a one-dimensional lattice with a homogeneous coin matrix. This skeleton structure is independent of the initial state, and partially, even of the coin matrix. This structure is best interpreted in the context of quantum-walk-replicating random walks (QWRWs), i.e., random walks that replicate the probability distribution of quantum walks, where this structure acts as a simplified formula for the transition probability. Additionally, we construct a random walk whose transition probabilities are defined by the skeleton structure and demonstrate that the resultant properties of the walkers are similar to both the original QWs and QWRWs.

In this paper, we analyze the statistics of detection data in a general double-double-slit experiment. The two particles are detected at random times which are not equal in general and because we do not have any constraint on the distances of left and right screens from their slits and the ratio they can be detected in completely different timescales. As the detection of the first particle leads to collapse of the wave function, there is no a straightforward and agreed-upon method to study this problem in the orthodox formalism which lacks a clear prediction of these random events and therefore the quantum state afterward. This is not the case in the Bohmian framework which we implement in this paper, and we can predict the system up to the end of experiment. The main result is the joint distribution of detection data including the arrival time and position of the particles on left and right screens. As one of the main consequences, we see that although the joint spatial distribution can be affected by a change to the relative location of screens, the marginals on each side remain intact, compatible with signal locality. At the end, we see how this result is very sensitive to quantum equilibrium conditions.

The electronic stopping power of magnesium for protons and He ions is studied by a nonequilibrium approach based on real-time time-dependent density-functional theory combined with Ehrenfest molecular-dynamics simulation. The electronic stopping power of Mg for energetic protons and He ions is calculated, and the microscopic excitation mechanism for the inner $2p$ electron of Mg and its contribution to electronic stopping power is revealed. In the low-energy range, the velocity proportionality of the electronic stopping power of Mg for protons is displayed. The low-energy stopping power of Mg for He ions displays deviations from the velocity proportionality, which is ascribed to the electronic structure of He ions that enables an additional energy-loss channel due to charge exchange. Our calculated stopping power is in a quantitative agreement with the experimental data up to the stopping maximum, and the stopping power including also $2p$-electron excitation is considerably improved compared to that with only the valence electron taken into account. Our results showed that the contribution of $p$-electron excitation to the electronic stopping is remarkable in the high-velocity regime. The scaling relationship $\sqrt{S_{\alpha }/S_H}$ = ${\overline{q}}_{\alpha }/{\overline{q}}_H$ can be extended to low velocities provided that the mean steady-state charge is employed instead of assuming fully ionized charges and considering also $2p$-electron excitation of Mg.

We study the behavior of the excitation spectrum across the quantum phase transition from a superfluid to a supersolid phase of a dipolar Bose gas confined to a one-dimensional geometry. Including the leading beyond-mean-field effects within an effective Hamiltonian, the analysis is based on Bogoliubov theory with several order parameters accounting for the superfluid as well as solid structure. We find fast convergence of the ground-state energy in the supersolid with the number of order parameters and demonstrate a stable excitation spectrum with two Goldstone modes and an amplitude mode in the low-energy regime. Our results suggest that there exists an experimentally achievable parameter regime for dysprosium atoms, where the supersolid phase exhibits a stable excitation spectrum in the thermodynamic limit and the transition into the supersolid phase is of second order driven by the roton instability.

Simulating physics with large $\mathrm{SU}\left(N\right)$ symmetry is one of the unique advantages of alkaline-earth-metal atoms. Introducing periodical driving modes to the system may provide richer $\mathrm{SU}\left(N\right)$ physics that the static one cannot reach. However, a discussion of whether or not the driving modes will break the SU($N$) symmetry is still lacking. Here we experimentally study a Floquet engineered degenerate ${}^{87}\mathrm{Sr}$ optical lattice clock (OLC) by periodically modulating the frequency of the lattice laser. With the help of Rabi spectroscopy, we find that the atoms at different Zeeman sublevels are tuned by the same driven function. Meanwhile, our experimental results suggest that the uniform distribution among the sublevels does not change despite the driving. Our experimental demonstrations may pave the way for implementation of Floquet engineering on tailoring the $\mathrm{SU}\left(N\right)$ physics in the OLC system.

The generation of dissipative Kerr solitons (DKSs) in a passive fiber Kerr resonator with a fast saturable absorber (SA) is studied numerically. Simulation results demonstrate the generation of DKSs in SA-based fiber Kerr resonators. The impact of the properties of an SA, including the modulation depth and the saturation power, on the performances of DKSs is studied. Our results show the existence of DKSs in SA-based passive fiber Kerr resonators, suggesting that the SA provides additional degrees of freedom to get access to the DKS regime in Kerr resonators in addition to the detuning and the pump. These findings provide guidance for the experimental realization of the generation of DKSs in SA-based fiber Kerr resonators.

We propose to uncover the topology of a pseudo-Hermitian Chern insulator by quantum quench dynamics. The Bloch Hamiltonian of the pseudo-Hermitian Chern insulator is defined in the basis of the $q$-deformed Pauli matrices, which are related to the representation of the deformed algebras. We show the bulk-surface duality of the pseudo-Hermitian phases, then further build a concrete relation between the static band topology and quench dynamics, in terms of the time-averaged spin textures. The results are also generalized into a fully nonequilibrium case where the postquench evolution is governed by a Floquet pseudo-Hermitian Hamiltonian. Furthermore, we propose a possible scheme to realize the seemingly challenging model in a bilayer lattice and detect the dynamics with a double-quench protocol.

We introduce a generalized approach to characterize the non-Markovianity of quantum dynamical maps via breakdown of monotonicity of thermodynamic functions. By adopting an entropy-based formulation of quantum thermodynamics, we use the relationship between heat and entropy to propose a measure of non-Markovianity based on the heat flow for single-qubit quantum evolutions. This measure can be applied for unital dynamical maps that do not invert the sign of the internal energy. Under certain conditions, it can also be extended for other thermodynamic functions, such as internal energy and work flows. In this context, a natural connection between heat and quantum coherence can be identified for dynamical maps that are both unital and incoherent. As applications, we explore dissipative and nondissipative quantum dynamical processes, illustrating the compatibility between our thermodynamic quantifiers and the well-establish measure defined via quantum coherence.

The question of whether quantum coherence is a resource beneficial or detrimental to the performance of quantum heat engines has been thoroughly studied but remains undecided. To isolate the contribution of coherence, we analyze the performance of a purely coherence-driven quantum heat engine, a device that does not include any heat flow during the thermodynamic cycle. The engine is powered by the coherence of a multiqubit system, where each qubit is charged via interaction with a coherence bath using the Jaynes-Cummings model. We demonstrate that optimal coherence charging and hence extractable work is achieved when the coherence bath has an intermediate degree of coherence. In our model, the extractable work is maximized when four copies of the charged qubits are used. Meanwhile, the efficiency of the engine, given by the extractable work per input coherence flow, is optimized by avoiding the coherence being stored in the system-bath correlations that is inaccessible to work. We numerically find that the highest efficiency is obtained for slightly lower temperatures and weaker system-bath coupling than those for optimal coherence charging.

We investigate the open dynamics of a probe qubit weakly interacting with distinct qubit environments bearing quantum information. We show that the proposed dissipative model yields a binary classification of the reservoir qubits' quantum information in the steady state in the Bloch qubit parameter space, depending on the coupling rates. To describe the dissipation model dynamics, we have adopted the collision model, in which the input information parameters of the reservoir qubits are easily determined. We develop a generalized classification rule based on the results of the micromaserlike master equation where the classification can be described in terms of the Bloch parameters. Moreover, we show that the proposed classification scheme can also be achieved through quantum parameter estimation. Finally, we demonstrate that the proposed dissipative classification scheme is suitable for gradient descent-based supervised learning tasks.