We demonstrate an approach to the generation of custom entangled many-body states through reservoir engineering, using the symmetry properties of bosonic lattice systems coupled to a local squeezed reservoir [Yanay and Clerk, Phys. Rev. A 98, 043615 (2018)]. We outline an algorithm where, beginning with a desired set of squeezing correlations, one uses the symmetry to constrain the Hamiltonian and find a lattice configuration which stabilizes a pure steady state realizing these correlations. We demonstrate how to use this process to stabilize two unique pure states with nonlocal correlations that could be useful for quantum information applications. First, we show how to drive a square lattice into a product state of entangled quadruplets of sites. Second, using a bisected system, we generate a steady state where local measurements in one half of the lattice herald a pure delocalized state in the second half.

Noncontextual Pauli Hamiltonians decompose into sets of Pauli terms to which joint values may be assigned without contradiction. We construct a quasiquantized model for noncontextual Pauli Hamiltonians. Using this model, we give an algorithm to classically simulate the noncontextual variational quantum eigensolver. We also use the model to show that the noncontextual Hamiltonian problem is NP-complete. Finally, we explore the applicability of our quasiquantized model as an approximate simulation tool for contextual Hamiltonians. These results support the notion of noncontextuality as classicality in near-term quantum algorithms.

We have measured fully momentum-analyzed recoiling target ions and scattered projectiles, produced in ionization of He and ${\mathrm{H}}_2$ by 75 keV proton impact, in coincidence. The momentum of the ejected electrons was deduced from momentum conservation. From the data we extracted fully differential ionization cross sections as a function of the polar electron emission angle (for fixed electron energies) and as a function of the electron energy (for fixed electron emission angles). Comparison between experiment and various distorted wave calculations confirms that under kinematic conditions where the post-collision interaction plays an important role, the few-body dynamics underlying the ionization process are still poorly understood.

Collisional ionization between two Rydberg atoms in relative motion is examined. A classical trajectory Monte Carlo method is used to determine the cross sections associated with Penning ionization. The dependence of the ionization cross section on the magnitude and the direction of orbital angular momentum of the electrons and the direction of the Laplace-Runge-Lenz vector of the electrons is studied. For a given magnitude of angular momentum, there can exist a difference of a factor of up to $\sim 2.5$ in the ionization cross section between the orientations with the highest and the lowest ionization cross section. The case of exchange ionization is examined and its dependence on the magnitude of angular momentum is studied.

We describe a quantum simulator for the Hubbard-Holstein model (HHM), comprising two dressed Rydberg atom species held in a monolayer by independent painted potentials, predicting that boson-mediated preformed pairing and Berezinskii-Kosterlitz-Thouless (BKT) transition temperatures are experimentally accessible. The HHM is important for modeling the essential physics of unconventional superconductors. Experimentally realizable quantum simulators for HHMs are needed (1) since HHMs are difficult to solve numerically and analytically, (2) to explore how competition between electron-phonon interactions and strong repulsion affects pairing in unconventional superconductors, and (3) to understand the role of boson-mediated local pairing in pseudogaps and fermion condensates. We propose and study a quantum simulator for the HHM, using optical lattices, painted using zeros in the ac Stark shift, to control two Rydberg atom species independently within a monolayer. We predict that interactions are sufficiently tunable to probe (1) both HHMs and highly unconventional phonon-mediated repulsions, (2) the competition between intermediate-strength phonon- and Coulomb-mediated interactions, and (3) BKT transitions and preformed pairing that could be used to examine key hypotheses related to the pseudogap. We discuss how the quantum simulator can be used to investigate boson-mediated pairing and condensation of fermions in unconventional superconductors.

In this paper, we propose a predictor or indicator of the self-healing ability of coherent structured light beams: the field's modal content. Specifically, the fidelity between the obstructed and unobstructed beams' modal spectrum serves as a useful measure of the degree to which the beam will likely self-heal after an arbitrary obstacle. Since any optical field can be decomposed in terms of any chosen orthonormal basis, this analysis is, therefore, less restrictive than other methods for determining self-healing ability. Furthermore, since modal content is propagation invariant, this allows beam self-reconstruction to be studied in this way at any available transverse plane. As a case study, we present convincing experimental evidence for the superiority of the self-healing properties of Laguerre-Gaussian over Bessel-Gaussian beams, analysis that is facilitated primarily by the proposed measure.

Circular dichroism (CD) caused by the response of a chiral object to circularly polarized light has been well established, and the strong CD of plasmonic metamolecules has also become of interest in recent years; however, their response if the light also has orbital angular momentum is unclear. In this paper, the dichroism of a plasmonic cuboid-protuberance chiral structure under the illumination of a light beam with both orbital and spin angular momenta is numerically investigated. Distinguished spectra are observed under the different momenta. The circular dichroism under the combination of vortex beam and light spin is enhanced. This phenomenon is attributed to the partial spatial excitation of the nanoparticle, and the strong dichroism is simultaneously caused because of the interaction of the induced electric and magnetic modes and other higher-order modes caused by the partial excitation of the vortex beam. This research provides further insight into chiral light-matter interactions and the dichroism of light with orbital angular momentum.

The Dicke model famously exhibits a phase transition to a superradiant phase with a macroscopic population of photons and is realized in multiple settings in open quantum systems. In this paper, we study a variant of the Dicke model where the cavity mode is lossy due to the coupling to a Markovian environment while the atomic mode is coupled to a colored bath. We analytically investigate this model by inspecting its low-frequency behavior via the Schwinger-Keldysh field theory and carefully examine the nature of the corresponding superradiant phase transition. Integrating out the fast modes, we can identify a simple effective theory allowing us to derive analytical expressions for various critical exponents including the dynamical exponent. We find excellent agreement with previous numerical results when the non-Markovian bath is at zero temperature; however, contrary to these studies, our low-frequency approach reveals that the same exponents govern the critical behavior when the colored bath is at finite temperature unless the chemical potential is zero. Furthermore, we show that the superradiant phase transition is classical in nature, while it is genuinely nonequilibrium. We derive a fractional Langevin equation and conjecture the associated fractional Fokker-Planck equation that captures the system's long-time memory as well as its nonequilibrium behavior. Finally, we consider finite-size effects at the phase transition and identify the finite-size scaling exponents, unlocking a rich behavior in both statics and dynamics of the photonic and atomic observables.

The logarithmic negativity of a bipartite quantum state is a widely employed entanglement measure in quantum information theory due to the fact that it is easy to compute and serves as an upper bound on distillable entanglement. More recently, the $\kappa$ entanglement of a bipartite state was shown to be an entanglement measure that is both easily computable and has a precise information-theoretic meaning, being equal to the exact entanglement cost of a bipartite quantum state when the free operations are those that completely preserve the positivity of the partial transpose [Xin Wang and Mark M. Wilde, Phys. Rev. Lett. 125, 040502 (2020)]. In this paper, we provide a nontrivial link between these two entanglement measures by showing that they are the extremes of an ordered family of $\alpha$-logarithmic negativity entanglement measures, each of which is identified by a parameter $\alpha \in \left[1,\infty \right]$. In this family, the original logarithmic negativity is recovered as the smallest with $\alpha =1$, and the $\kappa$ entanglement is recovered as the largest with $\alpha =\infty$. We prove that the $\alpha$-logarithmic negativity satisfies the following properties: entanglement monotone, normalization, faithfulness, and subadditivity. We also prove that it is neither convex nor monogamous. Finally, we define the $\alpha$-logarithmic negativity of a quantum channel as a generalization of the notion for quantum states, and we show how to generalize many of the concepts to arbitrary resource theories.

Time evolution of spin-orbit-coupled cold atoms in an optical lattice is studied, with a two-band energy spectrum having two avoided crossings. A force is applied such that the atoms experience two consecutive Landau-Zener tunnelings while transversing the avoided crossings. Stückelberg interference arises from the phase accumulated during the adiabatic evolution between the two tunnelings. This phase is gauge field dependent and thus provides new opportunities to measure the synthetic gauge field, which is verified via calculation of spin transition probabilities after a double-passage process. Time-dependent and time-averaged spin probabilities are derived, in which resonances are found. We also demonstrate chiral Bloch oscillation and rich spin-momentum locking behavior in this system.

We conduct a theoretical study of the propagation of few-cycle ultrafast vortices (UFVs) carrying orbital angular momentum (OAM) in free space. Our analysis reveals much more complex temporal dynamics than that of few-cycle fundamental Gaussian-like beams, particularly when approaching the single-cycle regime and the magnitude of the topological charge $l$ is high. The recently described lower bound $\sqrt{\left|l\right|}$ to the number of oscillations of UFVs with propagation-invariant temporal shape (isodiffracting UFVs) is found to hold on average also for UFVs of general type, with variations along the propagation direction above and below that bound, even vanishing locally. These variations are determined by the so-called Porras factor, or $g_0$ factor, characterizing the dependence of the Rayleigh distance of the spectral constituents with frequency. With a given available bandwidth, UFVs must widen temporally with increasing magnitude of the topological charge and must widen or may shrink temporally during propagation as a result of the axially varying $g_0$-dependent lower bound. Under very restrictive conditions in their generation, an UFV can be shrunk below the lower bound $\sqrt{\left|l\right|}$ at a focus into a kind of locally compressed state of OAM, but it broadens well above $\sqrt{\left|l\right|}$ and is distorted in a tiny fraction of the depth of focus because of the dispersions introduced by Gouy's phase and wave-front mismatch. These propagation phenomena have implications and should be taken into account in experiments and applications of UFVs, such as the generation of high harmonics and attosecond pulses with high OAM, or in OAM-based ultrafast communications systems, as well as in other areas of physics such as acoustics or electron waves.

We observe and analyze formation, decay, and subsequent regeneration of ring-shaped clusters of (2+1)-dimensional spatial solitons (filaments) in a medium with cubic-quintic (focusing-defocusing) self-interaction and strong dissipative nonlinearity. The cluster of filaments, which remains stable over $\approx 17.5$ Rayleigh lengths, is produced by the azimuthal modulational instability from a parent ring-shaped beam with embedded vorticity $l=1$. In the course of still longer propagation, the stability of the soliton cluster is lost under the action of nonlinear losses. The annular cluster is then spontaneously regenerated due to power transfer from the reservoir provided by the unsplit part of the parent vortex ring. Thus, a secondary interval of the robust propagation of the regenerated cluster is identified. The experiments use a laser beam (at wavelength 800 nm), built of pulses with temporal duration 150 fs, at the repetition rate of 1 kHz, propagating in a cell filled by liquid carbon disulfide. Numerical calculations, based on a modified nonlinear Schrödinger equation which includes the cubic-quintic refractive terms and nonlinear losses, provide results in close agreement with the experimental findings.

We develop a nonequilibrium field-theoretical approach based on a systematic diagrammatic expansion for strongly interacting photons in optically dense atomic media. We consider the case where the characteristic photon-propagation range $L_P$ is much larger than the interatomic spacing $a$ and where the density of atomic excitations is low enough to neglect saturation effects. In the highly polarizable medium, the photons experience nonlinearities through the interactions they inherit from the atoms. If the atom-atom interaction range $L_E$ is also large compared to $a$, we show that scattering processes with momentum transfer between photons are suppressed by a factor $a/L_E$. We are then able to perform a self-consistent resummation of a specific (Hartree-like) diagram subclass and obtain quantitative results in the highly nonperturbative regime of large single-atom cooperativity. Here we find important, collective phenomena emerging due to the dissipative nature of the interactions, which even give rise to novel phase transitions. The robustness of these is investigated by inclusion of the leading corrections in $a/L_E$. We consider specific applications to photons propagating under EIT conditions along waveguides near atomic arrays as well as within Rydberg ensembles.

We investigate the absorption and transmission properties of a weak probe field under the influence of a strong control field in a cavity magnomechanical system. The system consists of two ferromagnetic-material yttrium iron garnet (YIG) spheres coupled to a single cavity mode. In addition to two magnon-induced transparencies (MITs) that arise due to magnon-photon interactions, we observe a magnomechanically induced transparency (MMIT) due to the presence of nonlinear magnon-phonon interaction. We discuss the emergence of Fano resonances and explain the splitting of a single Fano profile to double and triple Fano profiles due to additional couplings in the proposed system. Moreover, by considering a two-YIG system, the group delay of the probe field can be enhanced by one order of magnitude as compared with a single-YIG magnomechanical system. Furthermore, we show that the group delay depends on the tunability of the coupling strength of the first YIG with respect to the coupling frequency of of the second YIG, and vice versa. This helps to achieve larger group delays for weak magnon-photon coupling strengths.

Spontaneous synchronization is a collective phenomenon that can occur in both dynamical classical and quantum systems. Here, we analyze the spontaneous synchronization dynamics of vibrations assisting energy transfer in a bio-inspired system. We find the emergence of a constant nonzero “synchronization phase” between synchronized vibrational displacements as the natural frequencies of the oscillators are detuned. This phase difference arises from the asymmetric participation of local modes in the long-lived synchronized state. Furthermore, we investigate the relationships between the synchronization phase, detuning and the degree of quantum correlations between the synchronizing subsystems and find that the synchronization phase captures how quantum correlations persistently exceed classical correlations during the dynamics. We show that our analysis applies to a variety of spontaneously synchronizing open quantum systems. Our work therefore opens up a promising avenue to investigate nontrivial quantum phenomena in complex biomolecular and nanoscale chemical systems.

We show the enhancement of a distillable key rate for quantum key distribution (QKD) by local filtering for several bound entangled states. Through our paper, it becomes evident that the local filtration operations, whereas transforming one bound entangled state to another, have the potential to increase the utility of the new state for QKD. We demonstrate three examples of “one-way distillable key rate” enhancement by local filtering and, in this process, discover new bound entangled states which are key distillable.

We study how single-qubit dispersive readout works alongside two-qubit coupling. To make calculations analytically tractable, we use a simplified model which retains core characteristics of but is discretized compared to dispersive homodyne detection. We show how the measurement speed and power determine what information about the qubit(s) is accessed. Specifically we find the basis the measurement is closest to projecting onto. Compared to the basis in which gates are applied, this measurement basis is modified by the presence of photons in the readout resonator.

Water, the substance of life, is known for its myriad of anomalous properties, whose origins are still the subject of intense debates. In order to provide a different insight into this problem, we show how its density anomaly can be reproduced using a quantum simulator. In particular, we demonstrate that the Bose-Hubbard model, a paradigm system in quantum mechanics, exhibits an increase in density with temperature at fixed pressure in the regular fluid regime and in the superfluid phase. We propose that the mechanism underlying the anomalies is related to zero-point entropies and ground-state phase transitions. A connection with the typical experimental scales and setups including confinement effects is also addressed. In this scenario, such finding opens a pathway for theoretical and experimental studies of waterlike anomalies in the area of ultracold quantum gases.

The intrinsic optical response of a scattering object is known to be modified when it is placed on a substrate. Moreover, the total extinction through ohmic losses and Rayleigh scattering is basically dependent on the reversal of the direction of the excitation wave. Considering, as stated by the generalized optical theorem, that the total extinction of the incident wave is shared among the extinction of the waves transmitted and reflected by the non-absorbing substrate, we show that only the contribution of the transmitted wave is insensitive to the direction of illumination, by analogy with the textbook case of transmission through a planar stratified medium. This property was recently confirmed experimentally [J. Phys. Chem. C 123, 15217 (2019)] and is established here on theoretical grounds in the frameworks of the Green's function integral equation method and the Lorentz reciprocity theorem. Some of its limitations with regard to the incidence and the polarization of the excitation wave are also discussed in detail.