The Hawking effect—the amplification of fluctuations at the horizon—has been detected in quantum fluids through real-space density correlations. However, real-space observables integrate over frequency, mixing distinct scattering channels into a single interference pattern and obscuring the spectral and entanglement structure of the emission. Here, we numerically compute momentum-space two-point correlations in a transcritical quantum fluid, using the truncated Wigner approximation applied to a realistic, driven-dissipative polariton system. We spectrally resolve the Hawking-partner channel as well as graybody factor channels and find that both carry comparable correlation strength, demonstrating that the well-known real-space “moustache” is an interference between these spectrally distinct contributions. The Hawking-partner channel is dominated by negative correlations, a direct signature of quantum-vacuum pair creation. All features reach amplitudes detectable in state-of-the-art experiments. Our results establish that the full three-mode output state must be considered for entanglement characterization, and they provide a general framework applicable to any quantum fluid.

Chiroptical responses in atomic systems are usually weak, as they arise from the interference between electric- and much weaker magnetic-dipole transitions. We show that atoms arranged in chiral geometries can instead exhibit a strong collective chiroptical response mediated entirely by electric-dipole interactions. Using a coupled-dipole framework, we identify a regime of pronounced chiroptical response emerging at subwavelength interatomic separations, which can be tuned by the probe frequency. This enhancement is directly linked to the formation of subradiant collective modes. Our results establish a fundamental connection between geometric chirality and collective light-matter interactions, opening additional pathways for engineering and exploiting chiral optical responses in atomic systems.

Classical objectivity requires an environment to witness a pointer value, not merely to decohere it. We derive microscopic Hamiltonian laws for this distinction. Exact quantum nondemolition product monitoring yields a certified two-edge strong-Darwinism window: sufficient witnesses cross the optimal record-discrimination edge while retaining an unobserved complement that crosses the residual-coherence edge. Under additional regularity assumptions, the supplement gives converse bounds at the same logarithmic scale. For controlled-phase monitors, environmental asymmetry gives a single-fragment information bound, a redundancy converse, and, in efficient i.i.d. streams, an achievable block-capacity law for redundant witnesses. A finite-temperature spin-phase bath shows the physical separation: hot probes can decohere efficiently while losing the local asymmetry needed for objective witnesses.

We present a class of control pulses designed to transfer colocated ensembles without relying on frequency selectivity, thereby allowing much faster state transitions. A geometric approach allows us to construct sequences which are robust to changes in the background magnetic field along multiple axes, and errors in the pulse area. These pulses are extremely fast, with robustness to pulse area shown at half the quantum speed limit. We demonstrate these sequences on nuclear-dipole states, showing milliradian precision over several hours, 30-fold beyond the previous state of the art. This provides a path for extending the coherent integration time of ultralong-lived nuclear-spin states to the fundamental limit set by their $>10000$ s lifetimes, as the limiting self-interactions of the nuclei are suppressed in the symmetric superposition. The state-preparation quality demonstrated here directly opens up 30-fold improvements in next generation tests of the standard model, especially tests of the symmetries of QCD and searches for dark matter; it is also crucial for the development of nuclear-spin-based quantum memories and may be useful in other scenarios demanding extremely fast but robust transitions.

Releasing shell-shaped Bose-Einstein condensates from the external confinement produces a spherically symmetric density distribution characterized by concentric ripples surrounding a central peak. Here, we investigate how a vortex-antivortex dipole affects this dynamics, finding that increasing dipole separation progressively breaks the spherical symmetry. Correspondingly, the interplay of vortex physics and curvature produces a nonmonotonic behavior of the cloud aspect ratio with the vortex distance, and decreases the maximal central density achieved during the expansion. These features can be used for detecting vortex dipoles prepared in shell-shaped superfluids, as well as a basis for analyzing their signatures in other thin superfluids with more general curved geometries.

Quantized transport usually occurs in linear periodic systems with nontrivial topology. While nonlinearity can strongly influence this transport, particularly through the formation of solitons, it is still determined by the spatiotemporal Chern indices of the bands of the underlying linear potential. Here, we show that nonlinear quantized transport can be induced by a sliding nonlinear lattice, even when the latter is combined with a static linear lattice, whose bands are topologically trivial. In such a system, an effective topology emerges from characteristic features of stable Wannier solitons and can be described in terms of the transport of Wannier centers associated with a composite potential combining the stationary linear lattice and an effective moving nonlinear lattice. The phenomenon is generic, as confirmed by the analysis of the continuous Gross-Pitaevskii equation with mutually sliding nonlinear and linear lattices, as well as by the corresponding discrete model with spatially varying coefficients. By increasing the norm of the input state, i.e., the nonlinearity strength, one can observe the unique transition from the absence of transport, to the topological transport, and, eventually, to the nontopological dragging of the input state by the nonlinear lattice.

We present a microscopic calculation of spontaneous photon emission by twisted (paraxial) electrons propagating through inhomogeneous, axisymmetric magnetic fields. We construct exact electron states that incorporate transverse mode structure and wave-front curvature by combining the Foldy-Wouthuysen transformation with a geometric framework based on Lewis-Ermakov invariants and metaplectic transformations. We show that the evolution of such structured states corresponds to an open path in the space of quadratic forms, giving rise to a geometric contribution to the emission amplitude that cannot be eliminated by gauge choice or adiabatic arguments. The inverse radius of curvature of the electron wave front controls a finite-window boundary contribution to the emission amplitude in regions where the external magnetic field vanishes locally; this contribution vanishes when the observation window is extended to infinity. The mechanism presented generalizes Landau-level radiation to nonasymptotic, structured electron states and establishes a direct connection between noncyclic geometric evolution and photon emission.

We investigate a noncylindrically symmetric vector optical field constructed in the orthogonal dipolar coordinate system. This field generates a spin-dependent transverse wave-vector shift, enabling a controllable optical spin Hall effect in tightly focused fields. We demonstrate that the separation distance between opposite spins can be continuously tuned by varying the topological order of the dipolar vector optical field. Furthermore, the separated spins give rise to an extraordinary optical force governed by the Belinfante spin momentum, which manifests itself as a customizable spin-curl force and drives nanoparticles in opposite directions depending on their spin state. This work establishes a geometric degree of freedom for engineering spin-orbit interactions, providing a powerful platform for chiral nanoparticle sorting and advanced spin-photomechanical devices.

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 $0.9951\left(9\right)$.