The presence of a magnetized element, say, a ferrite, or a magnetically biased plasmonic particle in a guiding medium leads to nonreciprocal behavior of the entire ambient surroundings. The nonreciprocity measure depends on the particle's excitation, which in turn depends on the magnetized material damping rate $\mathrm{\Gamma }$. Therefore, intuitively speaking, the heavier the material damping rate is, the weaker the nonreciprocal response. In this Letter, we reveal a more delicate mechanism demonstrating a loss-threshold phenomenon for nonreciprocity. Specifically, under certain conditions, we show that the nonreciprocity effect is robust against material loss up to a critical loss threshold ${\mathrm{\Gamma }}_{\mathrm{c}}$ that depends on the magnetization bias strength. Although this effect can be observed to some limited extent in the near field of the magnetized element, even in free space, its appearance when the magnetized particle is placed inside a cavity, as is often the case in nonreciprocal microwave devices, is substantially stronger and occurs with magnetization strength equivalent to cyclotron over plasma frequency as low as 5%–10% and with loss rates in the same order, thus making it measurable in various configurations and a wide range of frequencies from rf to low terahertz.

We present a theoretical study on the circular polarization of the $1s2s^{2}2p_{1/2}{J}_d=1\to 1s^{2}2s^2{J}_f=0$ electric-dipole emission following the resonant electron capture of lithiumlike ions with spin-polarized electrons. Special attention is paid to how the spin polarization of the recombined electrons influences the circular polarization of the emitted photons. To this end, detailed calculations are carried out for different spin-polarization states of the recombined electrons within the framework of the density-matrix theory by employing the multiconfigurational Dirac-Hartree-Fock and relativistic distorted-wave methods. We uncover that the emitted photons are strongly circularly polarized, exhibiting a pronounced sensitivity to the spin polarization of the recombined electrons, with a distinct dependence on the emission angle. The pronounced sensitivity of the circular polarization to the spin polarization of the recombined electrons can serve as a powerful diagnostic scheme for the spin polarization of electron beams. Beyond its fundamental significance, such a circular-polarization-resolved diagnostic scheme holds promising potential applications in plasma physics and materials science, enabling precise spin diagnostics in extreme plasmas and allowing the characterization of spin-related properties in magnetic materials.

We investigate a spin-degenerate Fermi gas coupled to a high-finesse optical cavity, where the competition between scalar and vectorial couplings is controlled by the relative polarization angle of the pump and cavity fields. We find that the phase transition threshold is synergistically determined by the scalar-vectorial coupling weight and Pauli blocking, with the latter dictating the critical pump lattice depth required for the onset of superradiance. For a two-component Fermi gas with opposite spins, the population ratio drives two distinct types of phase transitions corresponding to real-space phase separation: continuous and discontinuous. Nevertheless, the boundary of the phase transition remains fundamentally governed by the scalar-vectorial coupling competition. We clarify the impact of the relative polarization angle on phase transitions of the system; these results also apply to bosonic systems. Our results provide valuable theoretical insights for future experimental realizations.

Moiré photonic crystals support flatband modes with extreme field localization, offering a powerful platform for high-$Q$ microcavities and photonic devices. In realistic structures, however, finite size and unavoidable fabrication disorder break ideal translational symmetry and can strongly modify radiative loss. Here we investigate the radiative properties of flatband modes in a finite, single-cell three-dimensional photonic crystal, which represents the minimal functional moiré-type element of practical devices. By controlling the disorder level, we systematically investigate how the disorder strength affects the radiative loss and quality factor of moiré flatband modes. We find a pronounced nonmonotonic dependence of the average $Q$ factor on disorder, i.e., weak disorder initially enhances $Q$, while stronger disorder rapidly degrades it. Analysis of radiation channels reveals that slight disorder can manipulate the far-field radiation and suppress the radiative coupling, whereas larger disorder destroys the coherence of moiré interference, enhances multiple scattering, and drives energy into the radiation light cone, which leads to a pronounced increase in radiative loss. These results demonstrate the dual role of disorder in moiré flatband photonics and provide clear design guidelines for disorder-resistant high-$Q$ photonic devices.

The Mpemba effect, where a state farther from equilibrium relaxes faster than one closer to it, is a striking phenomenon in both classical and quantum systems. In open quantum systems, however, the quantum Mpemba effect (QME) typically occurs only for specifically chosen initial states, which limits its universality. Here we present a general and experimentally feasible strategy to realize both QME and anti-QME. By applying a temporary bond-dissipation quench, we selectively suppress or enhance slow relaxation modes, thereby reshaping relaxation pathways independently of both the system and the initial state. We demonstrate this mechanism in systems with dephasing and boundary dissipation, and we outline feasible cold-atom implementations. Our results establish controllable dissipation as a versatile tool for quantum control, accelerated relaxation, and efficient nonequilibrium protocols.

We present an effective theory for describing electron dynamics driven by an optical external field in a Schrödinger's cat state. We show that the reduced electron density matrix evolves as an average over trajectories $\left\{{\rho }_{\alpha }\right\}$ weighted by the Sudarshan-Glauber $P$ distribution $P\left(\alpha \right)$ in the weak light-matter coupling regime. Each trajectory obeys an equation of motion, $\mathrm{i}{\partial }_t{\rho }_{\alpha }={\mathcal{H}}_{\alpha }{\rho }_{\alpha }-{\rho }_{\alpha }{\mathcal{H}}_{\alpha }$, where an effective Hamiltonian ${\mathcal{H}}_{\alpha }$ becomes non-Hermitian due to quantum interference of light. The optical quantum interference is transferred to electrons through the asymmetric action between the ket and bra state vectors in ${\rho }_{\alpha }$. This non-Hermitian dynamics differs from the conventional one observed in open quantum systems, described by $\mathrm{i}{\partial }_t\rho =\mathcal{H}\rho -\rho {\mathcal{H}}^{†}$, which has complex conjugation in the second term. We confirm that the reduced, trajectory-resolved effective theory agrees with full electron-photon simulations for the few-electron Dicke model, thereby validating the interferential non-Hermitian description in the weak-coupling regime.

Different quantum systems possess different favorable qualities. On the one hand, ensemble-based quantum memories are suited for fast multiplexed long-range entanglement generation. On the other hand, single-atomic systems provide access to gates for processing of information. Both of those can provide advantages for high-rate entanglement generation within quantum networks. We develop a hybrid architecture that takes advantage of these properties by combining trapped-ion nodes and nodes comprised of spontaneous parametric down-conversion photon-pair sources and absorptive memories based on rare-earth ion ensembles. To this end, we solve the central challenge of matching the different bandwidths of photons emitted by those systems in an initial entanglement-generation step. This enables the parallel execution of multiple probabilistic tasks in the initial stage. As a particular example, we show that our approach can lead to a significant speed-up for the fundamental task of creating ion-ion entanglement over hundreds of kilometers in a quantum network.

Due to their photonic components, exciton-polariton systems provide a convenient platform to study the coherence properties of weakly interacting Bose gases. In particular, optical interferometry enables the measurement of the first-order coherence function, which provides information about the intrinsic correlations of the system. In this Letter, we derive a universal curve for the coherent fraction of a noninteracting, equilibrium, homogeneous, two-dimensional Bose gas, with density expressed in units of the observation area, and compare it to recent experimental results. Although there is a sharp transition from normal to superfluid phases in the thermodynamic limit, the coherent fraction of the gas varies continuously across this transition due to the finite system size. We find that the theory agrees nearly perfectly with the experimental data in the low-density limit with no free parameters other than the effective temperature, highly constrained by the measurements. At higher density, the experiments are consistent with standard weakly interacting Bose gas theory. By having a theory that treats both the optical diffraction and Bose coherence, we can clearly see the effect of the quantum statistics on the coherence.

Imaging molecular chirality in the strong-field regime requires understanding which stages of the photoelectron dynamics carry enantiosensitive information—and, ideally, controlling them independently. Here, we demonstrate that in rescattering photoelectron spectroscopy (RPES), which probes the photoelectron momentum distribution at the backward rescattering caustic, the enantiosensitive signal decomposes into two physically distinct contributions arising at the tunneling and rescattering stages, each reflecting the vortex structure of the photoelectron wave packet at that stage. In a phase-controlled two-color field, these contributions can be switched on and off independently by tuning a single experimental parameter, the relative phase. This elevates RPES from a structural probe to a stage-resolved chiroptical platform for imaging molecular chirality.

Toroidal dipole moments arise from poloidal current distributions and form a distinct class of electromagnetic excitations with unique near-field characteristics. Using Lorenz-Mie theory, we show that interference between conventional magnetic and magnetic toroidal dipoles in core-shell nanoparticles produces Fano resonances and pronounced forward-backward scattering asymmetry. By introducing optical gain in the dielectric core, we demonstrate that the toroidal mode can be selectively enhanced, enabling control of near-field confinement and far-field scattering directionality. As the gain varies, we find that the system undergoes a continuous transition from suppressed backscattering to suppressed forward scattering through an intermediate regime of dominant magnetic-dipole radiation. This dipolar scattering pattern is associated with a phase resonance of the magnetic toroidal dipole and a reversal of the poloidal current handedness. These results identify gain-controlled toroidal excitations as a tunable mechanism for directional scattering in nanoscale systems.

${}^{225}\mathrm{Ra}^{+}$ ions (nuclear spin $I=1/2$) have transitions that are first-order insensitive to magnetic field noise, which is advantageous for optical clocks and quantum information science. We report on laser cooling and trapping of ${}^{225}\mathrm{Ra}^{+}$ ions and hyperfine splitting measurements of the ion's $7\mathrm{s}{}^2{\mathrm{S}}_{1/2}$, $7\mathrm{p}{}^2{\mathrm{P}}_{1/2}$, and $6\mathrm{d}{}^2{\mathrm{D}}_{3/2}$ states. We measured the ground-state hyperfine constant, $A\left({\mathrm{S}}_{1/2}\right)=$ $-27.684511052\left(5\right)\mathrm{GHz}$, and the quadratic Zeeman coefficient, $C_2=142.3\left(1.0\right)$ $\mathrm{Hz}{\mathrm{G}}^{-2}$, of the ${}^2{\mathrm{S}}_{1/2}(F=0,m_F=0)\leftrightarrow {}^2{\mathrm{S}}_{1/2}(F=1,m_F=0)$ transition. Our result addresses a discrepancy in the literature for the ground-state hyperfine splitting. We measured the hyperfine constants of the ${}^2{\mathrm{P}}_{1/2}$ state, $A\left({\mathrm{P}}_{1/2}\right)=$ $-5.447\left(4\right)\mathrm{GHz}$, and the ${}^2{\mathrm{D}}_{3/2}$ state, $A\left({\mathrm{D}}_{3/2}\right)=$ $-619.7\left(1.1\right)\mathrm{MHz}$. We also performed state preparation and measurement using the ground-state hyperfine levels and realized a fidelity of $0.9951\left(9\right)$.

Recent works on the decoherent histories formalism suggest that slowly evolving macroscopic quantities (extensive sums of local observables) in quantum many-body systems can be consistently monitored: The existence of past measurements does not alter future outcome distribution. Here, for Gaussian weak measurements, we show that fluctuations of macroscopic quantities cannot be consistently monitored in general, in contrast to their intensive mean value. Exceptions include fluctuations at infinite temperature, at critical points, and in semiclassical systems. We analytically quantify nonconsistency in terms of susceptibility and obtain related results on entropy growth under noisy unitary.

Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of paraxial wave packets in reflection from a planar interface, known collectively as optical shifts, appear inevitable within the framework of the wave theory. Yet, we demonstrate that such shifts can be completely eliminated at a given angle of incidence at a planar interface of homogeneous dielectric and absorbing media by classically entangling phase-space degrees of freedom of an incident wave packet. Thus, we can attain a geometric optics limit in the wave-packet reflection from a single planar interface. We identify a set of plasmonic materials (noble metals) and a parameter regime for which such cancellation is robust to modest errors in the incidence angle and source coherence, as well as polarization, providing practical guidelines for tailoring transverse beam displacements and angular deviations with standard metallic coatings.

We directly measure the branching ratio of the $5s4d{}^1{D}_2\to 5s5p{}^3{P}_2$ transition and the decay rate of the $5s5p{}^1{P}_1\to 5s4d{}^1{D}_2$ transition in neutral strontium. For more than four decades, these quantities lacked an experimental determination independent of theoretical input. We measure the branching ratio to be 0.177(4), significantly lower than the widely cited theoretical value of 0.322 [C. W. Bauschlicher, Jr. et al., J. Phys. B: At. Mol. Phys. 18, 1523 (1985)]. We also determine the decay rate to be $5.3\left(5\right)\times {10}^3{\mathrm{s}}^{-1}$, consistent with the value reported by Hunter et al. [Phys. Rev. Lett. 56, 823 (1986)] but substantially lower than the recent theoretical prediction of $9.25\left(40\right)\times {10}^3{\mathrm{s}}^{-1}$ [A. Cooper et al., Phys. Rev. X 8, 041055 (2018)]. These measurements provide an experimental benchmark for quantitative modeling of loss processes in laser cooling and single-atom fluorescence detection in optical tweezers with Sr.

We report a differential momentum measurement of nonsequential double ionization (NSDI) of Mg in strong laser fields, by combining laser ablation with the supersonic molecular beam technique. The experimental result shows that the momentum distribution of ${\mathrm{Mg}}^{2+}$ ions along the laser polarization exhibits a single-peaked structure. This finding, confirmed by our fully classical model, provides direct experimental evidence that the NSDI of Mg proceeds predominantly via the recollision excitation with a subsequent ionization pathway. Furthermore, we find a distinct discrepancy in the shape of the momentum distribution obtained from the experiment and the classical model. The discrepancy mainly arises from the inability of the model to account for the returning electron impact ionization and excitation cross sections. Our experimental approach can be readily extended to other atomic species that are solid at room temperature. It also has important implications for probing electron entanglement in NSDI of alkaline-earth metal atoms.

The Josephson diode, a nonreciprocal quantum element analogous to the familiar semiconductor p–n junction diode, has been realized in solid-state systems. However, it remains relatively unexplored in atomtronic circuits, which, in contrast to the solid state, allow real-time, in situ, and tunable control over key elements such as junction geometry, current-phase relationship, symmetry breaking, and interaction-induced nonlinearity. In this Letter, we propose and numerically demonstrate the realization of the Josephson diode effect in an atomtronic circuit consisting of a ring-shaped Bose-Einstein condensate and with optical barriers serving as Josephson junctions. Our implementation of this macroscopic nonreciprocal quantum phenomenon is based on realizing the required inversion symmetry breaking through asymmetric barrier placement and an asymmetric alternating current drive, enabling position- and drive-tunable diode effects with efficiencies up to 20% and 91%, respectively. While standard time-of-flight absorption imaging can readily observe these effects, we employ cavity optomechanics for cleaner, in situ, real-time, and nondestructive measurements of the relevant condensate dynamics. Our results establish a highly tunable platform for nonreciprocal Josephson transport, opening avenues for diode-based neutral-atom technologies in future quantum circuits.

We introduce the correlation-efficient time-evolution (CETE) algorithm for simulating quantum many-body dynamics. CETE recasts each step of time evolution as a time-independent correlation problem: the ansatz begins from a mean-field single Slater determinant and is then correlated to capture the true time-evolved state. We derive this exact ansatz from a contraction of the time-dependent Schrödinger equation onto the space of two electrons. Unlike conventional evolution by sequential short-time propagators, which must both correlate and decorrelate the state as the degree of correlation fluctuates in time, CETE correlates only once. This substantially reduces circuit depth, extending accessible simulation times on near-term quantum devices. We demonstrate the approach by simulating the electronic time evolution of the hydrogen molecule and the helium hydride ion, highlighting the potential for the CETE algorithm to simulate strongly correlated systems on near-term devices.

Quantum sensing with qubits has advanced fundamental physics searches, but higher dimensional systems offer largely unexplored potential. We show that in ultralight dark matter searches spin-1 NV-center qutrits exploiting common mode noise suppression achieve an order of magnitude improvement in axion-electron coupling sensitivity over qubit-based schemes. While enhanced quantum Fisher information in multilevel systems is known abstractly, we demonstrate its explicit realization in a realistic open quantum system via an optimal protocol saturating the Cramer-Rao bound, yielding a universal fourfold enhancement. This principle applies broadly to multilevel quantum platforms, including superconducting, neutral atom, and trapped-ion systems, establishing higher dimensional sensing as a powerful probe of new physics.