Achieving precise control of ultracold atomic gases requires a detailed understanding of atom loss mechanisms. Motivated by the anomalous three-body decay in a three-component Fermi gas reported by Schumacher et al. [arXiv:2301.02237], this work investigates mechanisms that possibly contribute to the observed loss. The three-body Schrödinger equation is solved in the hyperspherical adiabatic representation with pairwise van der Waals interactions, and the $S$ matrix is obtained via the eigenchannel $R$-matrix method to compute recombination rate coefficients $K_3$ and two-body cross sections. At the magnetic-field strength where the anomalous decay occurs, $K_3$ is unitary limited, exhibiting the threshold energy scaling $K_3\left(E\right)\propto E^{-1}$ that applies when only one scattering length is resonant. Consequently, the thermally averaged $\langle K_3\rangle$ acquires a temperature dependence. Because the experiment is performed in the degenerate regime, $\langle K_3\rangle$ also explicitly depends on the per-spin densities through the per-spin Fermi energies $E_F^{\left(i\right)}\propto n_i^{2/3}$. As the gas is diluted and degeneracy is reduced, $\langle K_3\rangle$ approaches the nondegenerate value and becomes a function of temperature only. Channel-resolved branching ratios and cross sections are folded into a Monte Carlo cascade simulation of secondary collisions and trap escape. The analysis indicates that typical three-body recombination events remove fewer than three atoms on average and that the atom losses are primarily due to the ejection of secondary collision products rather than the initial three-body recombination products. Therefore, a significant fraction of the released binding energy remains in the trapped ensemble as kinetic energy. Retained energy drives evaporative loss, offering a plausible, partial explanation for the anomalous decay.

We propose to use cavity Rydberg electromagnetically induced transparency to generate Schrödinger cat states of optical photons. We predict that this should make it possible to generate states with relatively large mean photon numbers. With existing technology, mean photon numbers around 30 seem feasible. The main limitation is photon loss during the process, which generates the state. The ability to tune the strength of the photon loss caused by atomic spontaneous emission makes it possible to have little decoherence despite significant photon loss during the generation of the state.

We investigate the Coulomb explosion dynamics of ${\mathrm{H}}_2$ molecules embedded in helium nanodroplets, induced by an intense ultraviolet femtosecond laser pulse. By employing ion-ion coincidence and momentum correlation spectroscopy, we identify the Coulomb-exploded double ionization of ${\mathrm{H}}_2$ molecules within the droplets. Our results demonstrate that the collisions between dissociating ${\mathrm{H}}^{+}$ ions and surrounding He atoms significantly alter both the kinetic energy distributions and the emission direction of the ion fragments. Notably, the $\mathrm{He}{\mathrm{H}}^{+}$ fragments originating from the Coulomb explosion channel exhibit higher kinetic energies in larger droplets, a phenomenon driven by the solvation dynamics that depend on the fragment's kinetic energy and droplet size. This study provides deep insights into the translation, dissociation, and solvation processes of light impurities in quantum liquid, underscoring the critical role of droplet size in shaping fragment kinetics during these processes.

We report the creation of an ultracold gas of bosonic ${}^{39}\mathrm{K}{}^{133}\mathrm{Cs}$ molecules. We first demonstrate a cooling strategy relying on sympathetic cooling of ${}^{133}\mathrm{Cs}$ to produce an ultracold mixture. From this mixture, weakly bound molecules are formed using a Feshbach resonance at 361.7 G. The molecular gas contains $7.6\left(10\right)\times {10}^3$ molecules with a lifetime of about 130 ms, limited by two-body decay. We perform Feshbach spectroscopy to observe several new interspecies resonances and characterize the bound state used for magnetoassociation. Finally, we fit the combined results to obtain improved K-Cs interaction potentials. This provides a good starting point for the creation of ultracold samples of ground-state ${}^{39}\mathrm{K}{}^{133}\mathrm{Cs}$ molecules.

Ultracold dipolar atoms and molecules provide a flexible quantum simulation platform for studying strongly interacting many-body systems. Determining microscopic Hamiltonian parameters of the simulator is crucial for it to be useful. We study effective interactions emerging in quasi-one-dimensional (q1D) dipolar quantum gases, revealing significant nonuniversal corrections to the commonly used 1D pseudopotential. We demonstrate that a full 3D treatment employing realistic interaction potentials is essential for describing the reduced-dimensional system. Our findings are particularly relevant to experiments probing excited states and nonequilibrium phenomena.

The formation and properties of a supersolid structure in a three-component ultracold Bose gas mixture at $T=0$ are investigated theoretically. The system consists of ${}^{23}\mathrm{Na}$, ${}^{39}\mathrm{K}$, and ${}^{41}\mathrm{K}$ atomic species, in which the binary mixtures of (${}^{23}\mathrm{Na},{}^{39}\mathrm{K}$) and (${}^{39}\mathrm{K},{}^{41}\mathrm{K}$) can form self-bound quantum droplets stabilized by quantum fluctuations. Two such droplets can bind together by the shared ${}^{39}\mathrm{K}$ component, forming a stable “dimer” structure, which displays vibrational modes analogous to a classical diatomic molecule. A simple protocol is proposed to create a stable linear chain formed by periodic repetition of this basic building block, i.e., an alternating sequence of (${}^{23}\mathrm{Na},{}^{39}\mathrm{K}$) and (${}^{39}\mathrm{K},{}^{41}\mathrm{K}$) droplets. This structure exhibits both periodic density modulations from the droplet ordering and global phase coherence due to the shared ${}^{39}\mathrm{K}$ component, satisfying the criteria for supersolidity. This expands the class of known supersolids by adding a system where mediated binding—rather than intrinsic long-range interactions or engineered band structures as in previously known supersolids—is the key organizing principle, thereby offering alternative directions for both theory and experiment. The low-energy excitation spectrum, probed by density perturbations, identifies modes corresponding to droplet vibrations close to the ones expected from a classical diatomic chain, coexisting with low-energy superfluid (Goldstone-type) modes.

We investigate a phase-controllable mechanism for generating optical torque in a five-level double-tripod (DT) atom-light coupling scheme interacting with four strong coherent control fields as well as two weak optical vortex probe beams carrying orbital angular momentum (OAM). The spatial phase gradients of the OAM-carrying probes induce a quantized torque that is transferred to the atoms, rotating them and generating a directed atomic flow within an annular geometry. Analytical solutions of the optical Bloch equations under steady-state conditions show that the induced torque and resulting rotational motion exhibit high sensitivity to phase variations. We show that the DT system coherently reconfigures into either coupled-$\mathrm{\Lambda }$ or double-$\mathrm{\Lambda }$ schemes depending on the relative phases, with each configuration exhibiting distinct quantized torque characteristics. This enables precise phase control of the atomic current flow, with potential applications in quantum control, precision measurement, and quantum information processing.

Spontaneous parametric down-converters (SPDCs) are the best available entanglement sources for distributing entanglement in a quantum internet. However, their intrinsically probabilistic nature, and their need to operate at low brightness to suppress multipair events, dictate that multiplexed SPDC arrays are required for high-rate distribution in that application. Early SPDC multiplexing proposals involved path switching, whose switching losses significantly degrade performance. The present paper proposes and analyzes a scheme for spectral multiplexing that provides entanglement-distribution rates well in excess of the state of the art. It builds on zero-added-loss multiplexing (ZALM) [Phys. Rev. Appl. 19, 054029 (2023)] for high-rate heralded entanglement generation, which does not require a switched array of SPDCs. Our ZALM's SPDCs rely on nonlinear crystals with $N_I$ phase-matched spectral islands, each generating two-mode squeezed-vacuum states. Also, our ZALM's multiplexing protocol uses both same-island and cross-island heralding, which allows the entanglement-delivery rate to approximately scale as $N_I^2$ in the realistic weak-squeezing regime. As a result, our scheme uses an order of magnitude fewer spectral channels than the original ZALM proposal, which may enable near-term implementations of satellite-to-ground or fiber-optic based ZALM architectures.

In one-dimensional bosonic quantum mixtures with a SU(2)-symmetry-breaking Hamiltonian, the dynamical evolution explores different particle-exchange-symmetry sectors. For the case of infinitely strong intraspecies repulsion, the hallmark of such symmetry oscillations is time modulations of the momentum distribution [Musolino et al., Phys. Rev. Lett. 133, 183402 (2024)], an observable routinely accessed in experiments with ultracold atoms. In this work we show that this phenomenon is robust in strongly interacting quantum mixtures with an arbitrary interspecies-to-intraspecies interaction-strength ratio. Taking as the initial state the ground state of the SU(2)-symmetric Hamiltonian and time evolving with the symmetry-breaking Hamiltonian, we analyze how the amplitude and frequency of symmetry oscillations, and thus of the momentum-distribution oscillations, depend on the strength of the symmetry-breaking perturbation. We find that the set of symmetry sectors which are coupled during the time evolution is dictated by the spin-flip symmetry of the initial state and show that the population of the initial state may vanish periodically, even in the thermodynamic limit, thus revealing the robustness and universality of the symmetry oscillations.

We demonstrate that the Fourier transform of a function leads to interference effects in phase space which allow the reconstruction of the essential properties of the original function, even when we restrict the inverse Fourier transform to the phase factor rather than the complete Fourier transform. We analyze this phase-only reconstruction, known from signal processing, in quantum mechanics for the elementary example of a superposition of two real-valued Gaussians. We employ the Wigner function as well as techniques of semiclassical quantum mechanics to show that their key features, such as their separation and their width, are indeed encoded in the phase of the Fourier transform. For this example, the amplitude-only reconstruction performing the inverse Fourier transform of the absolute value of the Fourier transform fails.

We propose an effective scheme to enhance $N$-photon bundle emission of the squeezed mode via parametric driving. By placing a ${\chi }^{\left(2\right)}$ nonlinear medium and a typical two-level qubit into a cavity, the atom-cavity coupling strength is greatly enhanced while an additional squeezed reservoir is introduced to suppress noise amplification. As a consequence, it is demonstrated that the emitted probabilities of two-photon bundles are obviously increased, whereas the purity remains nearly unchanged. Remarkably, even for the more challenging case of three-photon bundles, our scheme still achieves a significant enhancement in their generation. The light resource with squeezed photons may find potential applications in quantum sensing technology and quantum metrology.

We report the production of an intense and controlled beam of electronically excited sulfur atoms in the ${}^{1}D_2$ state using a multistage Zeeman decelerator. Sulfur atoms, generated via photolysis of ${\mathrm{CS}}_2$, are produced in both the ground ${}^{3}P_J$ and excited ${}^{1}D_2$ states. We demonstrate that both can be manipulated using the decelerator, and that temporal separation between them can be achieved by operating in deceleration mode. This enables the generation of sulfur atom beams with a well-defined velocity, narrow velocity spreads, and an enhanced quantum-state purity. To assess the suitability of the beam for scattering studies, we performed a proof-of-principle elastic collision experiment with $\mathrm{S}\left({}^{1}D_2\right)$ and argon atoms. The observed velocity-map-imaging signal confirms that the $\mathrm{S}\left({}^{1}D_2\right)$ beam density is sufficient for detailed scattering studies. These results form the foundation for future studies of reactive and quenching processes involving $\mathrm{S}\left({}^{1}D_2\right)$ atoms at tunable and well-defined collision energies.

Entangled photon pairs are key elements in quantum communication and quantum cryptography. State-of-the-art sources of entangled photons are mainly based on parametric down-conversion from nonlinear crystals, which is probabilistic in nature, and on cascade emission from biexciton quantum dots, which finds difficulties in generating entangled photons in the visible regime. Here, we use the Wigner-Weisskopf theory to provide a demonstration that polarization-entangled photon pairs can be emitted from two interacting quantum emitters with two-level-system behavior and perpendicular transition dipole moments. These emitters can represent a large variety of systems (e.g., organic molecules, quantum dots, and diamond color centers) offering a large technological versatility, for example, in the spectral regime of the emission. We show that a highly entangled photon pair can be postselected from this system by including optical filters. Additionally, we verify that the photon entanglement is not significantly affected by small changes in the detection directions and in the orientation between the dipole moments.

The polarization of incident light may be tuned with the Brewster effect that is widely used in photography and optical coatings. The Brewster angle demonstrating zero reflection is usually observed for transverse-magnetic polarized light, but recent studies have discovered the generalized Brewster effect in transverse-electric polarization using nanostructures. In this work, we discover the way of the Brewster angle and perfect absorption control in transverse-electric polarization with two-dimensional plasmonic materials and nanostructures. We derive the analytical model of the reflectionless metasurface described by the surface conductivity within and beyond the total internal reflection state leading to the perfect absorption and generalized Brewster's angle, respectively. Then, we support our analytical results by the full-wave numerical simulation using the effective two-dimensional sheet obeying the Drude-Lorentz dispersion model and the real design of plasmonic anisotropic metasurface based on gold nanodisks. The results obtained open new opportunities for the planar polarization optics and related devices including polarization transformers, optical isolators, antireflection coatings, and biodetectors.

We propose and implement a protocol to measure the state-dependent motion of Rydberg atoms induced by dipole-dipole interactions. Our setup enables simultaneous readout of both the atomic internal state and position on a one-dimensional array of optical tweezers. We benchmark the protocol using two atoms in the same Rydberg state, which experience van der Waals repulsion, and measure velocities in agreement with theoretical predictions. When preparing the atoms in a different pair state, we observe an oscillatory dynamics that we attribute to the proximity of a macrodimer bound state. Finally, we perform a Stern-Gerlach-like experiment in which a superposition of the two previous pair states results in the separation of the atomic wave packet into two macroscopically distinct trajectories, thereby demonstrating spin-motion coupling mediated by the interactions.

We study the temporal dynamics of light interacting with a one-dimensional lattice of cold atoms. In such a system, a photonic band gap opens up, yielding an efficient Bragg reflection for an incident field incoming with the right angle and detuning. Here, we report two new effects appearing in the Bragg reflection. First, for some detunings, there is a “flash,” i.e., a transient increase of the reflected intensity when the incident field is switched off. Second, the subsequent extinction of the reflected field is clearly superradiant, with decay rates up to eight times the natural decay rate of the atomic excited state. Numerical simulations are in qualitative agreement with the observations, which can be explained by a classical photonic model. Our results are a step towards exploiting this photonic band gap in atomic systems for quantum-optical applications.

Information obtained from noise characterization of a quantum device can be used in classical decoding algorithms to improve the performance of quantum error-correcting codes. Focusing on the surface code under local (i.e., single-qubit) noise, we present a versatile, numerical method to quantify the performance improvement gained by adapting an optimal surface-code decoder to specific, user-defined features of the physical noise model. Our method is based on a tensor-network decoding algorithm, which uses the syndrome information as well as a process matrix description of the noise to compute a near-optimal correction. By selectively mischaracterizing the noise model input to the decoder and measuring the resulting loss in fidelity of the logical qubit, we can determine the relative importance of individual noise parameters for decoding. We apply this method to several physically relevant uncorrelated noise models with features such as coherence, spatial inhomogeneity, and bias. While noise generally requires many parameters to describe completely, we find that to achieve near-optimal decoding it appears only necessary to adapt the decoder to a small number of critical parameters.

We investigate a quantum metrological protocol operating in a non-Markovian environment by employing the quantum Brownian motion model, in which the system is linearly coupled to a reservoir of harmonic oscillators. Specifically, we use a position-momentum (PM) correlated Gaussian state as a probe to examine how memory effects influence the evolution of the system's covariance matrix in the weak-coupling regime under both high- and low-temperature conditions. To confirm the presence of non-Markovian behavior, we apply two well-established non-Markovianity quantifiers. Furthermore, we estimate both the channel's sample temperature and its non-Markovianity witness parameter. Our results demonstrate that non-Markovianity and PM correlations can jointly be valuable resources to enhance metrological performance.

We present a quantum theory of a magneto-optical trap (MOT) from first principles based on the quantum kinetic equation for the atomic density matrix, taking into account the recoil effects caused by the interaction of atoms with the laser field. An efficient method for solving the quantum kinetic equation is proposed. It is shown that the steady-state solution describing the atoms in the MOT has a significantly nonequilibrium nature and can be described within the framework of a two-temperature distribution. The momentum distribution of cold atoms in the MOT depends on the magnetic field gradient and, in general, significantly differs from the momentum distribution of atoms in the optical molasses, which is usually used as an approximation to describe the MOT. We have also shown that with an increase in the magnetic field gradient, a spatial two-component distribution of atoms in the trap is formed even for a single-particle approximation when interatomic interactions are neglected.

We investigate strong-field-induced electronic coherences in argon and molecular nitrogen ions created by high-intensity, few-cycle infrared laser pulses. This is a step toward the long-sought goal of strong-field coherent control in molecular chemistry. We employ high-intensity, few-cycle infrared laser pulses in a pump-probe setup to investigate a recent prediction that electronic coherences in nitrogen molecules change the ion yields versus pump-probe delay. [Yuen et al., Phys. Rev. A 109, L011101 (2024)]. The predicted coherence signals in molecular nitrogen could not be resolved above the optical interference of the pump and probe pulses; a simultaneous measurement clearly resolved the induced cation fine-structure coherence in strong-field-ionized argon. The results of our comparison with simulations suggest that optical interference effects manifest differently in each ionic species and must be carefully accounted for when interpreting experimental data. We find that nonsequential double ionization in the low-intensity region of the focal volume can reduce the visibility of coherence generated by two-pulse sequential ionization, and we quantify the importance of pulse shape and spectral characteristics for isolating the desired coherence signals.