We introduce a quantum control method for superconducting transmon qubits that substantially outperforms conventional techniques in precision and robustness against coherent errors. Our approach leverages composite pulses (CPs) to effectively mitigate system-specific errors, such as qubit frequency and anharmonicity variations. By utilizing CPs, we demonstrate both complete and partial population transfers between qubit states, as well as the implementation of two essential single-qubit quantum gates. Simulations reveal substantial reductions in common error rates and gate durations. The effectiveness of our method is validated through four independent verification techniques, underscoring its potential for advancing quantum computing with superconducting qubits.

We investigate how the quantum friction experienced by a polarizable atom moving with constant velocity parallel to a planar interface is modified when the latter consists of chiral or nonreciprocal media, with special focus on topological insulators. Macroscopic quantum electrodynamics is used to obtain the velocity-dependent Casimir-Polder frequency shift and decay rate. These results are a generalization to matter with time-reversal symmetry breaking. Our findings are illustrated by examining the nonretarded and retarded limits for five examples: a perfectly conducting mirror, a perfectly reflecting nonreciprocal mirror, a three-dimensional topological insulator, a perfectly reflecting chiral mirror, and an isotropic chiral medium. Different asymptotic power laws are found for all these materials. Interestingly, two bridges exist between chirality and nonreciprocity through the frequency shift, which arise as a consequence of the magnetoelectric coupling. Specifically, the position-dependent Casimir-Polder frequency shift for the nonreciprocal case depends on a geometric magnetic field associated with photoionization of chiral molecules, while the Casimir-Polder frequency shift depending on the velocity for the chiral case has the optical rotatory strength as the atomic response, and those for the nonreciprocal case depend on an analog of the optical rotatory strength.

We investigate the orientation dependence of enhanced ionization (EI) during strong-field-driven nuclear motion in acetylene (${\mathrm{C}}_2{\mathrm{H}}_2$). Here, we both initiate and probe molecular dynamics in acetylene with intense 6-fs cross-polarized pulse pairs, separated by a variable delay. Following multiple ionization by the first pulse, acetylene undergoes simultaneous elongation of the carbon-carbon and carbon-hydrogen bonds, enabling further ionization by the second pulse and the formation of a very highly charged state, [${\mathrm{C}}_2{\mathrm{H}}_2{]}^{6+}$. At small interpulse delays ($<20$ fs), this enhancement occurs when the molecule is aligned to the probe pulse. Conversely, at large delays ($>40$ fs), formation of [${\mathrm{C}}_2{\mathrm{H}}_2{]}^{6+}$ occurs when the molecule is aligned to the pump pulse. By analyzing the polarization and time dependence of sequentially ionized [${\mathrm{C}}_2{\mathrm{H}}_2{]}^{6+}$, we resolve two transient alignments that both contribute to a large increase in the multiple ionization yield. This cross-polarized pulse pair scheme uniquely enables selective probing of deeply bound orbitals, providing new insights on orientation-dependent EI in highly charged hydrocarbons.

In this paper, as a continuation of our recent article demonstrating that the $2p$ atom pair is entangled in the ${\mathrm{H}}_2$ photodissociation [Phys. Rev. A 111, 023116 (2025)], we have discovered the origins of the entanglement for the $2p$ atom-pair state and obtained the entanglement entropies by origins. The same investigation has been carried out for the precursor molecular state of the $2p$ atom pair. The reason for the increase of the entanglement entropy during the dissociation from the precursor molecule into the $\mathrm{H}\left(2p\right)+\mathrm{H}\left(2p\right)$ atom pair has been made clear.

This article evaluates the lens characteristics of a nonrotationally symmetric electron lens based on a ponderomotive potential, i.e., a ponderomotive lens, formed by intersecting one or more optical beams perpendicular to an electron beam. Based on geometric optics, design formulas are derived for the focal length and general spherical aberration coefficients of specifically crossed ponderomotive lenses. Numerical calculations demonstrate that a pair of these crossed ponderomotive lenses can effectively correct spherical aberration in the objective lens of an electron microscope. Unlike rotationally symmetric ponderomotive lenses, which require the optical beam to be coaxially aligned with the electron beam, the crossed ponderomotive lens avoids the need to place optical mirrors and lenses directly on the beam axis. Thus, it offers practical advantages in designing and building electron optical instruments and contributes to system miniaturization. With lens properties similar to multipole lenses, the proposed crossed ponderomotive lens is expected to facilitate diverse developments in electron optical systems incorporating ponderomotive potentials.

We investigate the photonic spin Hall effect (PSHE) and the Goos-Hänchen shift (GH shift) in semi-Dirac materials. Through theoretical modeling, we demonstrate that the anisotropic dielectric function in semi-Dirac materials plays a critical role in determining the magnitude and polarity of these optical displacements. Furthermore, by utilizing the unidirectional drift of massless Dirac electrons in semi-Dirac materials, we systematically reveal how the drift velocity and direction modulate the behavior of optical displacements. The results indicate that the unique electronic properties of semi-Dirac materials—particularly their anisotropic dielectric response and carrier drift dynamics—establish mechanisms for controlling optical displacements and polarization-dependent phenomena. This work opens a new avenue for designing advanced photonic devices with tunable optical responses, particularly with significant application potential in quantum information processing and topological photonics.

We develop a general approach to describe the scattering of quantum light by a lossy macroscopic object placed in vacuum with no restrictions on both its dispersive optical response and its spatially inhomogeneous composition. Our analysis is based on the modified Langevin noise formalism, a recently introduced version of macroscopic quantum electrodynamics where scattering $s$ modes are explicitly separated from electric $e$ and magnetic $m$ medium excitations; accordingly the formalism involves three kinds of noninteracting boson polaritons such that, in the lossless limit, $s$ polaritons reduce to standard photons whereas $e$ and $m$ polaritons disappear. We analytically derive the input-output unitary relation joining the boson operators of the ingoing and outgoing polaritons, a nontrivial result hinging upon original relations which comprehensively describe the transmission-emission-absorption interplay pertaining the classical radiation scattering, relations we here deduce by resorting to properties of the dyadic Green's function. Besides we exploit the input-output relation to connect the output state of the field to the input one, this unveiling the role played by various classical electromagnetic dyadics in quantum optical scattering. We specialize the discussion to the most common situation where the object is initially not electromagnetically excited, with the ingoing electromagnetic state only containing $s$ polaritons, and we analyze the impact of the classical transmission and absorption dyadics on the transitions from ingoing to outgoing $s$ polaritons and on the creation of outgoing $e$ and $m$ polaritons, respectively. Since the scattered radiation is collected in the far-field and the object is usually left unmeasured, we analytically derive the reduced density operator of the outgoing $s$ polaritons revealing, in particular, how object losses both produce quantum decoherence of the scattered radiation and enable to exploit the possible entanglement among ingoing $s$ polaritons to dramatically manipulate the statistical mixture of the quantum states pertaining to the scattered radiation.

We experimentally and theoretically study the formation of dressed states emerging from strong collective coupling of the narrow intercombination line of Yb atoms to a single mode of a high-finesse optical cavity. By permanently trapping and cooling the Yb atoms during their interaction with the cavity, we gain continuous experimental access to the dressed states. This allows us to detect both their field and their atomic properties, by simultaneously measuring the steady-state cavity transmission and free-space fluorescence. By varying the cavity and probe frequencies, we observe coupled atom-cavity states with atom-number-dependent splitting, the hallmark of collective strong coupling of the atoms with the single cavity mode. We find additional fluorescence output at atomic resonance, which we explain by the effects of dephasing and inhomogeneous broadening. We compare our experimental results with a theoretical model and find good qualitative agreement.

We investigate the generation of a triphoton state based on spontaneous six-wave mixing in cold atoms coherently driven by pumping, dressing, and coupling fields upon separate transitions. The designed energy-level structure largely suppresses linear absorption (Raman gain) of generated triphotons due to destructive interference (negligible excitation) and avoids stray biphotons arising from spontaneous four-wave mixing with appropriate atomic states and driving schemes. Numerical results show that two Stokes and one anti-Stokes photon, traveling respectively at the vacuum light speed and a reduced group velocity, can be simultaneously generated in a joint spectral region of two detunings exhibiting four resonances. Original third-order and reduced second-order time correlations of these photons suggest that one is an excellent messenger for heralding the existence of the other two, exhibiting a considerable generation rate and an obvious nonclassical feature.

We investigate the inseparability of states generated by superposition of a multipartite pure entangled state with a product state. In particular, we identify specific multipartite entangled states that will always produce inseparability after superposition with an arbitrary completely product state. Thus, these entangled states are unconditionally superposition robust, and we refer to this phenomenon as “unconditional inseparability of superposition” in multipartite quantum systems. In this way, we complete the picture of unconditional inseparability of superposition which was introduced earlier for bipartite systems. We also characterize the superposition of a multipartite pure entangled state with a pure biseparable state. However, the present analysis allows us to obtain a more general result, viz., there exists at least one pure entangled state in any multipartite Hilbert space such that its superposition with an arbitrary completely product state always yields an entangled state. On the other hand, for any bipartite pure entangled state, if at least one of the subsystems is a qubit, then it is always possible to find a suitable product state such that the superposition of the entangled state and the product state produces a product state. In this way, we find a feature of multipartite quantum systems which is in sharp contrast with that of bipartite ones. We then show how unconditional inseparability of superposition can be useful in exhibiting an indistinguishability property within the local unambiguous state discrimination problem.

The quantum Monte Carlo technique known as the stochastic series expansion (SSE) relies on a crucial no-branching condition: the SSE sampling is carried out in the computational basis, and the no-branching assumption ensures that superpositions of basis states do not appear when operators are applied. Without this proviso, the number of complex amplitudes would grow exponentially with the number of qubits and would eventually overwhelm the memory and processing power of a classical computer. However, the action of Clifford group elements on stabilizer states can be very efficiently described without resorting to an amplitude description. We explore how stabilizer states allow an extension of the SSE technique, and we give an example of a toy model that can be studied in this way. The method is also illustrated using the transverse-field Ising model.

A theoretical study of spin dynamics in nonrelativistic particle beams with interacting angular momenta traversing static, spatially varying magnetic fields is presented. The computational framework evaluates sinusoidal magnetic field configurations, calculating key observables such as average spin projections and state populations during the interaction. It is demonstrated that such fields can effectively enhance nuclear polarization in partially, incoherently polarized hydrogen and deuterium atomic beams, as well as coherently rotationally state-selected hydrogen deuteride molecular beams. This enhancement is attributed to transitions induced within the hyperfine regime of these systems. The study spans frequency ranges from gigahertz scales for atoms to hundreds of kilohertz for molecules, corresponding to magnetic field variations on spatial scales from submillimeters to meters.

This study presents an optimization technique for atomic structure calculations using the Flexible Atomic Code, focusing on complex multielectron systems relevant to $r$-process nucleosynthesis and kilonova modeling. We introduce a method to optimize the fictitious mean configuration used in the Flexible Atomic Code, significantly improving the accuracy of calculated energy levels and transition properties for lanthanide and actinide ions. Our approach employs a sequential model-based optimization algorithm to refine the fictitious mean configuration, iteratively minimizing the discrepancy between calculated and experimentally determined energy levels. We demonstrate the efficacy of this method through detailed analyses of Au ii, Pt ii, Pr ii, Pr iii, Er ii, and Er iii, representing a broad range of atomic configurations. The results show substantial improvements in the accuracy of the calculated energy levels, with average relative differences to the NIST data reduced from 20–60% to 10% or less for the studied ions. Transition wavelength calculations exhibit good agreement with experimental data, with about 90% of the calculated values falling within 10% of measurements for Pr and Er ions. While improvements in the transition probability calculations are observed, the calculated radiative transition probabilities. $\left[\log \right(gf$) values] still show significant discrepancies compared to the experimental data, with root-mean-square deviations of approximately 1.1–1.4 dex for Pr and Er ions. We extend our optimization technique to systematic calculations of singly and doubly ionised lanthanides, achieving accuracies comparable to or surpassing those of ab initio atomic structure codes. The method's broad applicability across the lanthanide series demonstrates its potential for enhancing opacity calculations and spectral modeling in astrophysical contexts.

The interplay of periodic driving and dissipation is a fundamental feature of nonequilibrium physics. We elaborate a scenario for the formation of dissipative multispot excitations (MSEs) in Kerr cavities, modeled by the one- and two-dimensional (1D and 2D) Lugiato-Lefever (LL) equations, which include a spatially periodic pump (SPP). First, we demonstrate that the SPP produces three alternative exact periodic solutions of the LL equation, expressed in terms of the $\mathrm{sn}$, $\mathrm{cn}$, and $\mathrm{dn}$ elliptic functions. By means of numerical methods, we explore the modulational instability (MI) and transverse instability (TI) of the periodic states in 1D and 2D settings, respectively. In the case of the defocusing nonlinearity, the 1D MI breaks the periodic states into an array of spatiotemporal crescents. In the case of self-focusing, the 1D MI, initiated by small random perturbations, leads to the establishment of a chaotic state, with the amplitude statistics featuring a long-tail probability distribution, that represents the presence of dissipative rogue waves. On the other hand, spatially periodic perturbations initiate the formation of breather chains, which periodically disappear and reappear, resembling the Fermi-Pasta-Ulam-Tsingou recurrence. In the 2D regime, the TI results in the formation of an array of 2D lumps. For a given SPP strength, the exact solutions for the periodic structures are stable if the loss constant exceeds a critical value. The findings reported here provide a contribution to nonequilibrium physics in general and may find direct applications in laser physics.

Abrupt time variations of the properties of optical materials have been at the center of intense research efforts in recent years, with the prospect of enabling extreme wave transformations and of leveraging time as a degree of freedom for wave control. While the most viable approach to yield ultrafast variations of the optical material response is through optical pumping of nonlinear media, the complex dynamics in these systems are not yet fully understood. Here, as a relevant case study of recent experimental observations, we rigorously investigate the pump-probe dynamics in a 310-nm-thick transparent conductive oxide etalon, using a weak 40-fs probe and a pump that displays peak power densities in the $\mathrm{TW}/\mathrm{c}{\mathrm{m}}^2$ range with a duration of a few femtoseconds. We examine the pump-probe interaction using a hydrodynamic Maxwell approach that accounts for diffraction, self-focusing and self-defocusing, self- and cross-phase modulation, probe gain, and linear and nonlinear material dispersion expanded in the perturbative regime up to ninth order for both pump and probe. By allowing the intricacies of the pump-probe interaction to proceed in time, we can also define an effective spatiotemporal permittivity for a more direct evaluation of the material ultrabroadband optical behavior. The reported results challenge the conventional modeling of this kind of problem, which has so far overlooked pump dynamics, simplistically assigning a local time-dependent refractive index to the probe that may be designed to fit the experimental data but has no physical connection to the complex pump-probe interaction. Our approach unveils new dynamics, pointing toward the possibility to achieve extreme pulse compression into the attosecond range and nonlinear diffraction over deeply subwavelength propagation distances, thus opening a possible new path toward novel and cost-effective tools for integrated photonics and attosecond science.

Two-color laser induced plasma filamentation in air could serve as tabletop sources of broadband terahertz (THz) pulses. Ubiquitous air in the earth facilitates its widespread utilities, particularly, in wireless communication and remote sensing, exploiting the unique advantage of the air-based scheme that the THz sources can be delivered over standoff distances via the pump laser propagation in air. However, the THz emission pattern inevitably has a conical angular profile with a dip in the propagation axis. Therefore, THz energy concentration, propagation directionality, and accuracy of signal demodulation are significantly impaired, greatly limiting its direct applications. Here, we successfully eliminate the unfavorable conical profile by experiments and meanwhile enhance THz directionality and intensity by 17 folds at the focus by use of abruptly autofocusing laser beams. Our simulations with a far-field model well reproduce the experimental observations, when the air filament length is read from the experimentally recorded fluorescence images. More importantly, we find that because the Gouy phase of Gaussian beam is ignored, the widely adopted dephasing length is significantly overestimated by 30 folds, which cannot explain the observed conical THz emission even when the filament length is shorter than the dephasing length. While the abruptly autofocusing beams are employed, the dephasing length is increased by five folds and the dephasing effect can be well overcome, which causes elimination of the unfavorable conical profile and enhancement of the THz intensity. This scheme is easily accessible since the abruptly autofocusing beam can be achieved by imposing a spatial light modulator on the input Gaussian beam.

We propose a liquid-crystal-filled microcavity system that enables polarization-selective control of exciton-polariton condensates. The structure consists of a microcavity with embedded perovskite layers, which are positioned to couple independently with orthogonally polarized cavity modes. This configuration allows for the engineering of independent stationary potentials for different polarization components. Using topology optimization, we design these potentials to shape the spatial distribution of polariton condensates, enabling smooth intensity gradation encoding in the emission profile. Our approach provides a versatile platform for polarization-sensitive optical processing and spatial light modulation.