Relative motion of structured optical illumination with respect to an object and far-field measurement of intensity are presented as a means to obtain far-subwavelength spatial resolution with a direct imaging arrangement. The principle behind this approach is that the variable interaction of an object with a background field generates information about nanometer-scale features that is encoded in the propagating plane-wave spectrum, allowing far-field data that are modulated with motion according to the nanostructure. Information theory supports this superresolution mechanism and illustrates sensitivity with respect to the illumination and detection arrangements. Simulations indicate that available lasers and detectors would enable a resolution of $\lambda /1000$ with modest signal-to-noise requirements and single-pixel detection. Relative motion in structured fields is shown to enhance spatial resolution achievable using data inversion with constraints. Importantly, far-subwavelength sensitivity is shown to be achievable even when the illuminating field is unknown. These results suggest applications that include material defect detection and unlabeled protein sensing, and direct extensions to estimating geometrical features at unprecedented spatial resolution become possible.

We investigate the capacity of the exact non-Rayleigh nondiffracting (ENRND) speckle field to reconstruct its statistical properties along the propagation. It is unclear in the literature how the statistical properties of such a speckle field can affect the reconstruction of the statistics itself after encountering an obstruction. Therefore, we have conducted this study using the first-order and second-order intensity statistics, revealing a remarkable superior robustness of the super-Rayleigh speckles. This study has the potential to be beneficial for future applications of speckles with controlled statistics in microscopic systems and quantum imaging.

Vibrational resonance is an interesting nonlinear phenomenon that has great potential in controllable weak signal enhancement. In this work we theoretically explore the possibility of amplifying a weak mechanical force via a vibrational-resonance mechanism in a cavity-optomechanical system. The results show that the weak force applied to the movable mirror can be dramatically amplified by adding a high-frequency mechanical force. Interestingly, we find that the amplification of the weak force can also be achieved by applying an extra optical field and the amplification peaks at optimal amplitude of the optical signal. Additionally, the influence of thermal noise on the mechanical oscillator is studied and numerical results demonstrate the feasibility of our proposal in a low-noise environment. Our findings offer an approach for amplifying a weak mechanical force by modulating an optical field in a cavity-optomechanical system.

Spectrally and spatially varying ensembles of emitters embedded into waveguides are ever-present in both well-established and emerging technologies. If control of collective excitations can be attained, a plethora of coherent quantum dynamics and applications may be realized on-chip in the scalable paradigm of waveguide quantum electrodynamics (WQED). Here, we investigate inhomogeneously broadened ensembles embedded with subwavelength spatial extent into waveguides employed as single effective and coherent emitters. We develop a method permitting the approximate analysis and simulation of such mesoscopic systems featuring many emitters, and show how collective resonances are observable within the waveguide transmission spectrum once their linewidth exceeds the inhomogeneous line. In particular, this allows for near-unity and tailorable non-Lorentzian extinction of waveguide photons overcoming large inhomogeneous broadening present in current state-of-the-art implementations. As a particular illustration possible in such existing experiments, we consider the classic emulation of the cavity QED (CQED) paradigm here using ensembles of rare-earth ions as coherent mirrors and qubits and demonstrate the possibility of strong coupling given existing restrictions on inhomogeneous broadening and ensemble spatial extent. This work introduces coherent ensemble dynamics in the solid state to WQED and extends the realm to spectrally tailorable emitters.

We consider the scenario of an emitter embedded in a nonideal cavity. Using an input-output approach to describe the open system, we show that an effective dissipative coupling between the emitter and the cavity can emerge because of their interaction with a common photonic environment. The underlying mechanism is independent of the nature of the emitter and exists even at zero temperature; hence our results provide a pathway for accessing a range of non-Hermitian phenomena in a variety of light-matter coupled systems. In particular, we show that the effective dissipative coupling can lead to the phenomenon of level attraction between the emitter and cavity mode when the radiative decay rates exceed the conventional Rabi coupling. Our model thus provides a possible explanation for the anomalous dispersions and negative mass observed in recent photoluminescence measurements in semiconductor microcavities. Finally, we show that our effective non-Hermitian system can produce hybrid light-matter exceptional points and bound states in the continuum.

We investigate the performance of a Stirling cycle with a working substance (WS) modeled as the quantum Rabi model (QRM), exploring the impact of criticality on its efficiency. Our findings indicate that the criticality of the QRM has a positive effect on improving the efficiency of the Stirling cycle when the WS parameters are in the normal phase. Furthermore, we observe that the Carnot efficiency is asymptotically achievable as the WS parameter approaches the critical point, even when both temperatures of the cold and hot reservoirs are finite. Additionally, we derive the critical behavior for the efficiency of the Stirling cycle, demonstrating how the efficiency asymptotically approaches the Carnot efficiency as the WS parameter approaches the critical point. Our work deepens the understanding of the impact of criticality on the performance of a Stirling heat engine.

The differential ${}^3\mathrm{He}^{2+}\text{−}\mathrm{He}$ scattering problem is investigated using the two-center wave-packet convergent close-coupling method in the incident energy range of 50–630 keV/u. The present two-electron approach accounts for electron exchange between reaction fragments and uses the configuration-interaction method to treat the target structure. We also apply a simpler method based on the effective one-electron target description. The singly differential cross sections are presented for electron capture, elastic scattering, excitation, and ionization of the target. The paper demonstrates the importance of the electron-electron correlation at lower projectile energies for the electron-capture and elastic-scattering processes. The two-electron results for electron capture into the ground state describe the available experimental data very well at all projectile energies, while the effective single-electron model shows good consistency at energies starting from 300 keV/u. For ionization, we observe a good level of agreement between the two approaches for all types of singly differential cross sections, and they agree well with the experimental data, wherever available. In addition, the angular differential cross sections for ground-state and total electron capture are presented for ${}^4\mathrm{He}^{2+}\text{−}\mathrm{He}$ collisions at the projectile energies of 62.5, 125, 187.5, and 250 keV/u. The angular differential elastic-scattering and excitation cross section and all three types of the singly differential ionization cross sections are found to be practically the same as the corresponding results for ${}^3\mathrm{He}^2\text{−}\mathrm{He}$ collisions.

Quantum turbulence indicators in dipolar Bose-Einstein condensed fluids, following emissions of vortex-antivortex pairs generated by a circularly moving detuned laser, are being provided by numerical simulations of the corresponding quasi-two-dimensional Gross-Pitaevskii formalism with repulsive contact interactions combined with tunable dipole-dipole strength. The critical velocities of two variants of a circularly moving obstacle are determined and analyzed for vortex-antivortex nucleation in the form of regular and cluster emissions. The turbulent dynamical behavior is predicted to follow closely the initial emission of vortex-antivortex pairs, relying on the expected Kolmogorov classical scaling law, which is verified by the spectral analysis of the incompressible part of the kinetic energy. Within our aim to provide further support in the investigations to date of quantum turbulence, which have been focused on nondipolar Bose-Einstein condensates, we emphasize the role of dipole-dipole interactions in the fluid dynamics.

In multipartite Bell scenarios, we study the nonlocality robustness of the Greenberger-Horne-Zeilinger (GHZ) state. When each party performs planar measurements forming a regular polygon, we exploit the symmetry of the resulting correlation tensor to drastically accelerate the computation of (i) a Bell inequality via Frank-Wolfe algorithms and (ii) the corresponding local bound. The Bell inequalities obtained are facets of the symmetrized local polytope and they give the best-known upper bounds on the nonlocality robustness of the GHZ state for three to ten parties. Moreover, for four measurements per party, we generalize our facets and hence show, for any number of parties, an improvement on Mermin's inequality in terms of noise robustness. We also compute the detection efficiency of our inequalities and show that some give rise to the activation of nonlocality in star networks, a property that was only shown with an infinite number of measurements.

The Weyl-Wigner formalism for evaluating the intrinsic information of Dirac bispinors as correlated qubits (localized) in a magnetic field is investigated in the extension to statistical ensembles. The confining external field quantizes the quantum correlation measures implied by the spin-parity qubit structure of the Dirac equation in $3+1$ dimensions, which simplifies the computation of the entanglement quantifier for mixed states in relativistic Landau levels. This allows for the evaluation of quantum and classical correlations in terms of entropy measures for Dirac structures that are eventually mixed. Our results are twofold. First, a family of mixed Gaussian states is obtained in phase space, and its intrinsic correlation structure is computed in closed form. Second, the partition function for the low-dimensional Dirac equation in a magnetic field is derived through complex integration techniques. It describes the low-temperature regime in terms of analytically continued zeta functions and the high-temperature limit as a polynomial on the temperature variable. The connection with lower dimensional systems is further elicited by mapping the spin-parity qubits to valley-sublattice bispinors of the low-energy effective Hamiltonian of graphene.

Noise is the main source that hinders us from fully exploiting quantum advantages in various quantum informational tasks. However, characterizing and calibrating the effect of noise is not always feasible in practice. Especially for quantum parameter estimation, an estimator constructed without precise knowledge of noise entails an inevitable bias. Recently, virtual purification-based error mitigation (VPEM) has been proposed to apply for quantum metrology to reduce such a bias occurring from unknown noise. While it was demonstrated to work for particular cases, whether VPEM always reduces a bias for general estimation schemes is unclear. For more general applications of VPEM to quantum metrology, we study factors determining whether VPEM can reduce the bias. We find that the closeness between the dominant eigenvector of a noisy state and the ideal quantum probe (without noise) with respect to an observable determines the reducible amount of bias by VPEM. Next, we show that one should carefully choose the reference point of the target parameter, which gives a smaller bias than others because the bias depends on the reference point. Otherwise, even if the dominant eigenvector and the ideal quantum probe are close, the bias of the mitigated case could be larger than the nonmitigated one. Finally, we analyze the error mitigation for a phase estimation scheme under various noises. Based on our analysis, we predict whether VPEM can effectively reduce a bias and numerically verify our results.

The silicon vacancy (${\mathrm{V}}_{\mathrm{Si}}$) in $3C$-SiC is studied as a center of interest in the field of quantum technologies, modeled as an electron spin (behaving as a two-state qubit in appropriate conditions) interacting through hyperfine coupling with the SiC nuclear spin bath containing ${}^{29}\mathrm{Si}$ and ${}^{13}\mathrm{C}$ nuclei in their natural isotopic concentration. We calculate the formation energies of the neutral and charged ${\mathrm{V}}_{\mathrm{Si}}$ with ab initio methods based on the density functional theory, identifying the stability of the neutral charge state for energies close to the valence band of $3C$-SiC. In addition, magnetic properties are calculated for the ${\mathrm{V}}_{\mathrm{Si}}^{-1}$ in $3C$-SiC and for ${\mathrm{V}}_{\mathrm{Si}}^0$ in both cubic and hexagonal SiC polytypes. We thereon evaluate, for the defect in the cubic polytype, the free induction decay and the Hahn-echo sequence on the electron spin interacting with the nuclear spin bath, shedding light on the electron spin-echo envelope modulation phenomenon and the decoherence effect by means of the cluster correlation expansion theory. We find a nonexponential coherence decay, which is a typical feature of solid-state qubits subjected to low-frequency $1/f$-type noise from the environment.

Magnetic-field-gradient-induced spin polarization transverse relaxation is re-examined in an alkali-metal atomic cell with antirelaxation coating. The experimentally observed motional-narrowing effect in a paraffin-coated vapor cell, a phenomenon for depicting the suppression of spin polarization transverse relaxation caused by the magnetic-field gradient, is more than an order of magnitude weaker than theoretical predictions. Such a discrepancy is due to the existence of background gas. By taking the background gas into consideration, Redfield theory combined with the Langevin approach is proposed to depict the magnetic-field-gradient-induced spin relaxation in a coated cell, and the model is verified to be consistent with the previous results derived under two limits in which the mean free path is either much smaller (diffusion regime) or much larger than (ballistic regime) the cell size. Our work provides a potentially feasible method to evaluate the background gas pressure inside the coated cell, and it can help to foster better comprehension of the performance of an antirelaxation coated cell.

We propose a generalized binary-encounter Bethe model (GBEB) based on corrected acceleration energies to predict the electron-impact ionization cross sections of molecules. The acceleration energy of the incident electron is inversely proportional to the molecular effective charge felt by the ejected electron. The symmetry of molecular orbitals is analyzed to determine the core and valence effective charges. We tested the GBEB model on several organic, inorganic, and atmospheric molecules with increasing complexity. The calculated total ionization cross sections are in better agreement with the experimental data than the predictions from the original BEB model. Another major advantage of the present model rests upon the convenience that it does not need any ad hoc correction used in previous BEB models.

The electron and ion properties observed in photoionization inherit the symmetry properties of both a target and radiation. Introducing symmetry breaking in the photoionization process, one can expect to observe a noticeable variation of the vector correlation parameters of either an outgoing photoelectron or a residual ion. One of the ways to violate symmetry is to irradiate matter by twisted radiation, which involves an additional screw. In the paper we present an extension of the approach developed in Phys. Rev. A 108, 023117 (2023) for photoelectron angular distribution to the other vector correlation parameters, specifically, photoelectron spin polarization, orientation, and alignment of the residual ion. Usually two conditions are needed to produce polarized photoelectrons: a system possesses a helix and a presence of noticeable spin-orbital interaction. Here, we investigate whether a twisted light brings an additional helicity to a system. As an illustrative example we consider ionization of a valence $4p$ shell of atomic krypton by circularly and linearly polarized Bessel light. The photoelectron spin components are analyzed as a function of the cone angle of twisted radiation.

We study quench dynamics of bosonic fractional quantum Hall systems in small lattices with cylindrical boundary conditions and low particle density. The states studied have quasiholes or quasiparticles relative to the bosonic Laughlin state at half-filling. Pinning potentials are placed at edge sites (or sites close to the edges) to trap quasiholes and qausiparticles. The potentials are then turned off, and because the edges of fractional quantum Hall systems host chiral edge modes, we expect chiral dynamics of the quasiholes and quasiparticles. We numerically show that chiral motion of the density distribution is observed and robust for the case with positive potentials (quasiholes), but that there is no noticeable chiral motion for negative potentials (quasiparticles). The comparison of the numerical ground states with model lattice Laughlin wave functions suggests that both positive and negative potentials do create and pin anyons that are not necessarily well separated on small lattices. Initializing the dynamics with the model state also shows the lack of chiral dynamics of quasiparticles. Our results suggest that, in small lattices with low particle density, quasiparticles are strongly adversely affected in dynamical processes, whereas quasiholes are dynamically robust.