We investigate the dynamical stability and real-time dynamics of the two types of ferrodark solitons (FDSs) which occur as topological magnetic domain walls in the easy-plane phase of a quasi-two-dimensional (2D) ferromagnetic spin-1 Bose-Einstein condensate. The type-I FDS has positive inertial mass and exhibits a single dynamical instability that generates in-plane spin winding, causing polar-core spin-vortex dipoles. The positive inertial mass leads to the elastic oscillations of the soliton under transverse perturbations. The type-II FDS has negative inertial mass and exhibits a snake instability and a spin-twist instability, with the latter involving the generation of out-of-plane spin winding. Distinct from the normal dynamics of negative mass solitons under long-wavelength transverse perturbations, the snake instability does not lead to the type-II FDS breaking down. Instead, segments of the type-II FDS convert to type-I and mass vortex dipoles are produced. The resulting hybridized chain of the two soliton types and vortices appears as a stable vortex–domain wall composite excitation and exhibits complex 2D dynamics at long times, while the vortices remain confined and the topological structure of a magnetic domain wall persists.

We present a method for deriving limits on Raman scattering in structured media and exploit it to constrain the maximum Raman signal resulting from a plane wave incident on either a single Raman molecule in the vicinity of a structured medium or a designable Raman medium. Results pertaining to metallic and dielectric structures illustrate the importance of accounting for the nonlinear interplay between pump and signal fields, showing that treating the pump-focusing and signal-extraction processes separately, as in prior work, leads to unrealistic enhancements. The formulation could readily find applications in further enhancing surface-enhanced Raman scattering (SERS) spectroscopy and Raman-assisted lasing.

Motivated by recent advances in the creation of few-body atomic Fermi gases with attractive interactions, we study theoretically the few-to-many-particle crossover of pair excitations, which for large particle numbers evolve into a mode that describes amplitude fluctuations of the superfluid order parameter (the “Higgs” mode). Our analysis is based on the hypothesis that salient aspects of the excitation spectrum are captured by interactions between time-reversed pair states in a harmonic oscillator potential. Microscopically, this assumption leads to a Richardson-type pairing model, which is integrable and thus allows a systematic quantitative study of the few-to-many-particle crossover with only minor numerical effort. We first establish a parity effect in the ground-state energy, i.e., a spectral convexity in the energy of open-shell configurations compared to their closed-shell neighbors, which is quantified by a so-called Matveev-Larkin parameter discussed for mesoscopic superconductors, which generalizes the pairing gap to mesoscopic ensembles and which behaves quantitatively differently in a few-body and a many-body regime. The crossover point for this quantity is widely tunable as a function of interaction strength. We then compute the excitation spectrum and demonstrate that the pair excitation energy shows a minimum that deepens with increasing particle number and shifts to smaller interaction strengths, consistent with the finite-size precursor of a quantum phase transition to a superfluid state. We extract a critical finite-size scaling exponent that characterizes the decrease of the gap with increasing particle number.

We investigate magneto-optical trap-loss spectroscopy of Rydberg excited ${}^{85}\mathrm{Rb}$ $(66\le n\le 68S_{1/2})$ atoms, placed inside a tailored microwave cavity. The cavity frequency at 13.053 GHz is in resonance with the $67S_{1/2}\to 66P_{3/2}$ transition, inducing a ladder multiphoton microwave Rydberg absorption and emission. The observed spectra are modeled with an extended Jaynes-Cummings formalism that accounts for nonlinear multiphoton absorption from and emission into the cavity, the loss from the trap due to Rydberg excitation, and cavity imperfection. We calculate the average photons in each spectral feature and find evidence for fractional photon emission into the cavity modes within the loss spectra. The microwave cavity Rydberg spectroscopy in this work provides key insights for advancing Rydberg-based sensors, quantum gates in hybrid systems, and the broader development of quantum technologies.

We propose a protocol in quantum illumination (QI) leveraging entanglement in discrete-variable states. Our investigation shows that, as $M\to \infty$, the $M$-mode Bell state matches the 6 dB advantage of the two-mode squeezed vacuum in high noise. It also excels in low- and mid-noise conditions, demonstrating that QI's benefits are not restricted to high background noise. Moreover, the protocol benefits from a sequential decision rule, increasing the advantage beyond 6 dB. These findings present an intriguing alternative to continuous-variable states and open different applications for QI using discrete-variable states.

The rich entanglement dynamics and transitions exhibited by monitored quantum systems typically only exist in the conditional state, making observation extremely difficult. In this Letter, we construct a general recipe for mimicking the conditional entanglement dynamics of a monitored system in a corresponding measurement-free dissipative system involving directional interactions between the original system and a set of auxiliary register modes. This mirror setup autonomously implements a measurement-feedforward dynamics that effectively retains a coarse-grained measurement record. We illustrate our ideas in a bosonic system featuring a competition between entangling measurements and local unitary dynamics, and also discuss extensions to qubit systems and truly many-body systems.

We propose a spectroscopic probe of the breaking and localization of Cooper pairs in an atomic Fermi superfluid interacting with a Rydberg impurity. This is achieved by monitoring the formation of diatomic and triatomic ultralong-range molecular species in the superfluid across the Bardeen-Cooper-Schrieffer (BCS)–Bose-Einstein condensation (BEC) crossover. The triatomic Rydberg molecule in the BEC regime heralds the trapping of a tightly bound Cooper pair, reminiscent of pion capture in nuclear matter, while the breaking of a Cooper pair on the BCS side by a diatomic Rydberg molecule is evocative of binary-star tidal disruption by a black hole. Spectroscopy of the Fermi superfluid and Rydberg molecules allows for an estimation of the Cooper-pair size while the Rydberg molecule binding energies discern many-body pairing effects.

We investigate the scattering properties and bound states of a quasi-two-dimensional (Q2D) spin-polarized Fermi gas near a $p$-wave Feshbach resonance. Strong confinement promotes the out-of-plane spatial wave function to an orbital degree of freedom with an energetic gap. Employing radio-frequency (rf) spectroscopy, we observe both power-law scaling and the dimensional-crossover feature that are indicative of an emergent $s$-wave interaction channel. Additionally, we demonstrate the formation of two types of low-energy dimers, possessing either $s$-wave or $p$-wave symmetry, through rf spin-flip association from an orbital mixture. Our observations are compared to predictions from a Q2D scattering model that incorporates exchange-antisymmetric orbital pair wave functions. These findings underscore how gapped orbital degrees of freedom can control scattering symmetry in strongly confined ultracold gases.

The Choi state is an indispensable tool in the study and analysis of quantum channels. Considering a channel in terms of its associated Choi state can greatly simplify problems. It also offers an alternative approach to the characterization of a channel, with properties of the Choi state providing novel insight into a channel's behavior. The rank of a Choi state, termed the Choi rank, has proven to be an important characterizing property, and here, its significance is further elucidated through an operational interpretation. The Choi rank is shown to provide a universal bound on how successfully two agents, Alice and Bob, can perform an entanglement-assisted exclusion task. The task can be considered an extension of superdense coding, where Bob can only output information about Alice's encoded bit string with certainty. Conclusive state exclusion, in place of state discrimination, is therefore considered at the culmination of the superdense coding protocol. In order to prove this result, a necessary condition for conclusive $k$-state exclusion of a set of states is presented in order to achieve this result, and the notions of weak and strong exclusion are introduced.

The study of state-to-state spin-exchange collisions near $p$-wave Feshbach resonances offers great opportunities to explore many-body interactions and novel quantum phases. Here, we report the observation of a spin-exchange collision near a $p$-wave Feshbach resonance within a mixture of the lowest and third-lowest hyperfine states of ${}^6\mathrm{Li}$ atoms. The spin-exchange interaction is observed over a range of 10 G and produces a pair of atoms in the second-lowest hyperfine states that are captured by a deep optical dipole trap. We apply a coupled-channel method to calculate the scattering properties of this system. We find that the $p$-wave resonance exhibits a low inelastic collision rate and a broad resonance profile, which is due to the modification by the accompanying spin-exchange collisions. These findings open up new possibilities for the creation of long-lived, strongly interacting $p$-wave Fermi gases.

Efficient sub-Doppler laser cooling and optical trapping of YO molecules offer new opportunities to study collisional dynamics in the quantum regime. Confined in a crossed optical dipole trap, we achieve the highest phase-space density of $2.5\times {10}^{-5}$ for a bulk laser-cooled molecular sample. This sets the stage to study YO-YO collisions in the microkelvin temperature regime, and reveal state-dependent, single-partial-wave two-body collisional loss rates. We determine the partial-wave contributions to loss of specific rotational states (first excited $N=1$ and ground $N=0$) following two strategies. First, we measure the change of the collision rate in a spin mixture of $N=1$ by tuning the kinetic energy with respect to the $p$- and $d$-wave centrifugal barriers. Second, we compare loss rates between a spin mixture and a spin-polarized state in $N=0$. Using quantum defect theory with a partially absorbing boundary condition at short range, we show that the dependence on temperature for $N=1$ can be reproduced in the presence of a $d$-wave or $f$-wave resonance, and the dependence on a spin mixture for $N=0$ with a $p$-wave resonance.

Subwavelength arrays of quantum two-level emitters have emerged as an interesting platform displaying prominent collective effects that can be harnessed for applications. Here, we study such arrays under strong coherent driving, realizing an open quantum many-body problem in a strongly nonlinear regime. For this we introduce an approach to this problem in terms of a dynamical mean-field theory, paving the way for further studies. We show that the spectrum of scattered light, characterized by the famous Mollow triplet for a single atom, develops a characteristic line shape with flat sidebands determined by dipolar interactions and relevant for experiments. Remarkably, this is to some extent independent of the specific geometry, but is sensitive to the ordered arrangement of the atoms. This line shape therefore characterizes atomic arrays and distinguishes them from disordered ensembles and noninteracting emitters.

We determine the phase diagram of a one-dimensional Bose gas in the presence of disorder with short- and long-range correlations, the latter decaying with distance as $1/{\left|x\right|}^{1+\sigma }$. When $\sigma <0$, the Berezinskii-Kosterlitz-Thouless transition between the superfluid and the localized phase is driven by the long-range correlations and the Luttinger parameter $K$ takes the critical value $K_c\left(\sigma \right)=3/2-\sigma /2$. The localized phase is a Bose glass for $\sigma >{\sigma }_c=3-{\pi }^2/3\simeq -0.289868$, and a Mott glass—characterized by a vanishing compressibility and a gapless conductivity—when $\sigma <{\sigma }_c$. Our conclusions, based on the nonperturbative functional renormalization group and perturbative renormalization group, are confirmed by the study of the case $\sigma =-1$, corresponding to a perfectly correlated disorder in space, where the model is exactly solvable in the semiclassical limit $K\to 0^{+}$.

Recent finite-temperature numerical simulations have unveiled a quantum “spin” microemulsion analog, found by raising the temperature of a stripe supersolid phase in a Rashba spin-orbit coupled Bose gas. This microemulsion state is a highly correlated, isotropic normal fluid where atoms self-arrange based on their internal pseudospin into patterns that resemble bicontinuous microemulsions. This finding leaves several open questions regarding the broader accessibility of this phase in experiments. Here, we use equilibrium finite-temperature numerical simulations based on a coherent-state path integral representation to perform a computational investigation into the thermodynamic stability of the spin microemulsion state. Numerical simulations emphasize the requirement of a nearly, but not perfectly, isotropic spin-orbit coupling in order to achieve the microemulsion phase in cold-atom experiments. Moreover, the microemulsion state exists independent of miscibility of the pseudospin components and for a wide range of pseudospin population imbalance, suggesting a high degree of flexibility in choosing the atom and hyperfine states in an experimental realization. Finally, we demonstrate this feasibility by mimicking a Rashba spin-orbit-coupled ${}^{87}\mathrm{Rb}$ experiment in an isotropic harmonic trap, where we confirm the microemulsion's existence via its density profile and equilibrium quasimomentum distribution.

Collective effects on the light scattered by disordered media such as Anderson localization and coherent backscattering critically depend on the reciprocity between interfering optical paths. In this Letter, we explore the breaking of reciprocity for the light scattered by a disordered cold-atom setup, taking advantage of the noncommutation of optical elements that manipulate the polarization of the interfering paths. This breaking of symmetry manifests itself in the reduction of the fringes' contrast as the light scattered by the cloud interferes with that from its mirror image. We provide a geometrical interpretation in terms of the Pancharatnam-Berry phase, which we directly access from the fringe displacement. Our work paves the way toward the manipulation of path reciprocity and interference of light using atomic media, where it could be combined with collective and saturation effects.

Low-frequency $1/f^{\alpha }$ charge noise significantly hinders the performance of voltage-controlled spin qubits in quantum dots. Here, we utilize fractional calculus to design voltage control pulses yielding the highest average fidelities for noisy quantum gate operations. We focus specifically on the exponential voltage control of the exchange interaction generating two-spin swap${}^k$ gates. When stationary charge noise is the dominant source of gate infidelity, we derive that the optimal exchange pulse is long and weak, with the broad shape of the symmetric $\mathrm{beta}$ distribution function with parameter $1-\alpha /2$. The common practice of making exchange pulses fast and high in amplitude still remains beneficial in the case of strongly nonstationary noise dynamics, modeled as fractional Brownian motion. The proposed methods are applicable to the characterization and optimization of quantum gate operations in various voltage-controlled qubit architectures.

Magic-state resource theory is a powerful tool with applications in quantum error correction, many-body physics, and classical simulation of quantum dynamics. Despite its broad scope, finding tractable resource monotones has been challenging. Stabilizer entropies have recently emerged as promising candidates (being easily computable and experimentally measurable detectors of nonstabilizerness) though their status as true resource monotones has been an open question ever since. In this Letter, we establish the monotonicity of stabilizer entropies for $\alpha \ge 2$ within the context of magic-state resource theory restricted to pure states. Additionally, we show that linear stabilizer entropies serve as strong monotones. Furthermore, we extend stabilizer entropies to mixed states as monotones via convex roof constructions whose computational evaluation significantly outperforms optimization over stabilizer decompositions for low-rank density matrices. As a direct corollary, we provide improved conversion bounds between resource states, revealing a preferred direction of conversion between magic states. These results conclusively validate the use of stabilizer entropies within magic-state resource theory and establish them as the only known family of monotones that are experimentally measurable and computationally tractable.

Quantum state preparation for trapped-ion qubits often relies on high-quality circularly polarized light, which may be difficult to achieve with chip-based integrated optics technology. We propose and implement a hybrid optical and microwave scheme for intermediate-field hyperfine qubits which instead relies on frequency selectivity. Experimentally, we achieve $99.94\%$ fidelity for linearly polarized $({\sigma }^{+}/{\sigma }^{-})$ light, using ${}^{43}\mathrm{Ca}^{+}$ at 28.8 mT. We find that the fidelity remains above $99.8\%$ for a mixture of all polarizations $({\sigma }^{+}/{\sigma }^{-}/\pi )$. We calculate that the method is capable of $99.99\%$ fidelity in ${}^{43}\mathrm{Ca}^{+}$, and even higher fidelities in heavier ions such as ${}^{\text{137}}\mathrm{Ba}^{+}$.

The simulation of synthetic dimensions by manipulating internal states of atoms and molecules has provided the opportunity to investigate regimes outside those of more traditional quantum many-body platforms. Highly excited Rydberg states of atoms are a particularly promising platform to engineer Hamiltonians in such synthetic dimensions due to their large number of addressable states and the readily available technologies for manipulating their couplings and for detecting them. In this Letter we demonstrate the realization of topological quantum pumping in synthetic dimensions by engineering a one-dimensional Rice-Mele chain from the Rydberg states of cesium atoms and manipulating their couplings in a time-dependent fashion through radio-frequency fields. We implement Thouless protocols for topological pumping and investigate the efficiency for pumping an effective quantum particle as a function of the period of pumping and other parameters while allowing for rates of change that are not necessarily adiabatic. We demonstrate that optimal pumping efficiencies of up to 90% can be achieved when the pump is operated in the topological Thouless regime, even when the pumping is accompanied by the wave-packet spread that arises from the energy dispersion of the particle along the synthetic dimension.