We realize the first magneto-optical trap of an atom in main group III of the Periodic Table. Our atom of choice (indium) does not have a transition out of its ground state suitable for laser cooling; therefore, laser cooling is performed on the $|5P_{3/2},F=6\rangle \to |5D_{5/2},F=7\rangle$ transition, where $|5P_{3/2},F=6\rangle$ is a long-lived metastable state. Optimization of our trap parameters results in atoms numbers as large as $5\times {10}^8$ atoms with temperatures of order 1 mK. Additionally, through trap decay measurements, we infer a one-body trap lifetime of $12.3\mathrm{s}$. This lifetime is consistent with background gas collisions and indicates that our repumpers have closed all leakage pathways. We also infer a two-body loss rate of $1.6\times {10}^{-11}{\mathrm{cm}}^3/\mathrm{s}$, which is comparable to those measured in alkali atoms. The techniques demonstrated in this Letter can be straightforwardly applied to other group-III atoms, and our results pave the way for realizing quantum degenerate gases of these particles.

Trapped ions form an advanced technology platform for quantum information processing with long qubit coherence times, high-fidelity quantum logic gates, optically active qubits, and a potential to scale up in size while preserving a high level of connectivity between qubits. These traits make them attractive not only for quantum computing, but also for quantum networking. Dedicated, special-purpose trapped-ion processors in conjunction with suitable interconnecting hardware can be used to form quantum repeaters that enable high-rate quantum communications between distant trapped-ion quantum computers in a network. In this regard, hybrid traps with two distinct species of ions, where one ion species can generate ion-photon entanglement that is useful for optically interfacing with the network and the other has long memory lifetimes, useful for qubit storage, have been proposed for entanglement distribution. We consider an architecture for a repeater based on such dual-species trapped-ion systems. We propose and analyze a protocol based on spatial and temporal mode multiplexing for entanglement distribution across a line network of such repeaters. Our protocol offers enhanced rates compared to rates previously reported for such repeaters. We determine the ion resources required at the repeaters to attain the enhanced rates, and the best rates attainable when constraints are placed on the number of repeaters and the number of ions per repeater. Our results bolster the case for near-term trapped-ion systems as quantum repeaters for long distance quantum communications.

We demonstrate the direct loading of a ${\mathrm{D}}_2$ magneto-optical trap (MOT) of potassium-39 atoms from a cryogenic buffer gas beam source. We load ${10}^8$ atoms in a 10 ms pulse, with no degradation in performance up to a 10 Hz repetition rate. Observed densities reach $\approx {10}^{11}$ atoms/${\mathrm{cm}}^3$ in a single pulse, achieved with a modest Zeeman slower but no sub-Doppler cooling or transverse compression. This system produces an ideal starting point for ultracold atom experiments where high experimental repetition rates are desirable and initial high densities are critical. Extension to other atomic species (e.g., refractory metals) that present technical challenges to high-yield production using oven-based sources is straightforward.

Optical beams with periodic lattice structures have broadened the study of structured waves. In the present work, we generate spin-orbit entangled photon states with a lattice structure and use them in a remote state preparation protocol. We sequentially measure spatially dependent correlation rates with an electron-multiplying intensified CCD camera and verify the successful remote preparation of spin-orbit states by performing pixel-wise quantum state tomography. Control of these structured waves in the quantum regime provides a method for quantum sensing and manipulation of periodic structures.

We show that the performance and functionality of atom chips can be transformed by using graphene-based van der Waals heterostructures to overcome present limitations on the lifetime of the trapped atom cloud and on its proximity to the chip surface. Our analysis involves Green's-function calculations of the thermal (Johnson) noise and Casimir-Polder atom-surface attraction produced by the atom chip. This enables us to determine the lifetime limitations produced by spin flip, tunneling, and three-body collisional losses. Compared with atom chips that use thick metallic conductors and substrates, atom-chip structures based on two-dimensional materials reduce the minimum attainable atom-surface separation to a few hundred nanometers and increase the lifetimes of the trapped atom clouds by orders of magnitude so that they are limited only by the quality of the background vacuum. We predict that atom chips with two-dimensional conductors will also reduce spatial fluctuations in the trapping potential originating from imperfections in the conductor patterns. These advantages will enhance the performance of atom chips for quantum sensing applications and for fundamental studies of complex quantum systems.

We report a spectroscopic investigation of the $3d{\delta }_{\mathrm{\Omega }}$ ($\mathrm{\Omega }=\frac{3}{2},\frac{5}{2}$) Rydberg states of the ${\mathrm{MgAr}}^{+}$ molecular cation. Vibrational levels of the $3d{\delta }_{3/2}$ spin-orbit component with $v\ge 15$ were observed to directly predissociate into charge-transfer continua correlating to the $\mathrm{Mg}\left(3s^2{}^{1}S\right)$ $+$ ${\mathrm{Ar}}^{+}\left(3p^5{}^{2}P\right)$ dissociation limit, making it possible to record their spectra by isolated-core multiphoton Rydberg dissociation spectroscopy. Vibrational states below $v=15$, which do not predissociate, were characterized with partial rotational resolution using a multiphoton excitation and dissociation quantum-control scheme that radiatively couples the $3d\delta$ vibronic states to predissociative levels of the $3d\pi$ state. An effective Hamiltonian approach was used to theoretically investigate this scheme, including the origin of the control over the spectral lineshapes provided by the laser detuning. This approach provided results in quantitative agreement with the measured spectra. Potential-energy functions were derived for the $3d{\delta }_{\mathrm{\Omega }}$ states from experimental data. They are very similar to the one of the $X^{2+}{}^1{\mathrm{\Sigma }}^{+}$ ground state of the ${\mathrm{MgAr}}^{2+}$ doubly charged ion, highlighting the Rydberg character of the $3d\delta$ state. Whereas homogeneous charge-transfer interactions play a major role in the dynamics of the Rydberg states of molecular ions, the present study shows that heterogeneous interactions leave these states essentially unaffected.

We study theoretically the nonlinear dynamics induced by shear-flow instability in segregated two-component Bose-Einstein condensates in terms of the Weber number, which is defined by extending the past theory on the Kelvin-Helmholtz instability in classical fluids. Numerical simulations of the Gross-Pitaevskii equations demonstrate that dynamics of pattern formation is well characterized by the Weber number We, clarifying the microscopic aspects unique to the quantum fluid system. For $\text{We}\lesssim 1$, the Kelvin-Helmholtz instability induces flutter-finger patterns of the interface and quantized vortices are generated at the tip of the fingers. The associated nonlinear dynamics exhibits a universal behavior with respect to We. When $\text{We}\gtrsim 1$ in which the interface thickness is larger than the wavelength of the interface mode, the nonlinear dynamics is effectively initiated by the counter-superflow instability. In a strongly segregated regime and a large relative velocity, the instability causes transient zipper pattern formation instead of generating vortices due to the lack of circulation to form a quantized vortex per a finger. In a weakly segregating regime and a small relative velocity, the instability leads to the sealskin pattern in the overlapping region, in which the frictional relaxation of the superflow cannot be explained only by the homogeneous counter-superflow instability. We discuss the details of the linear and nonlinear characteristics of this dynamical crossover from small to large Weber numbers, where microscopic properties of the interface become important for the large Weber number.

The Fermi National Accelerator Laboratory (FNAL) Muon $g-2$ Experiment has measured the anomalous precession frequency $a_{\mu }^{}\equiv (g_{\mu }^{}-2)/2$ of the muon to a combined precision of 0.46 parts per million with data collected during its first physics run in 2018. This paper documents the measurement of the magnetic field in the muon storage ring. The magnetic field is monitored by systems and calibrated in terms of the equivalent proton spin precession frequency in a spherical water sample at $34.7{}^{\circ }\mathrm{C}$. The measured field is weighted by the muon distribution resulting in ${\tilde{\omega }}_p^{\prime }$, the denominator in the ratio ${\omega }_a^{}$/${\tilde{\omega }}_p^{\prime }$ that together with known fundamental constants yields $a_{\mu }^{}$. The reported uncertainty on ${\tilde{\omega }}_p^{\prime }$ for the Run-1 data set is 114 ppb consisting of uncertainty contributions from frequency extraction, calibration, mapping, tracking, and averaging of 56 ppb, and contributions from fast transient fields of 99 ppb.

We investigate theoretically the strong-field regime of light-matter interactions in the topological-insulator class of quantum materials. In particular, we focus on the process of nonperturbative high-order harmonic generation from the paradigmatic three-dimensional topological insulator bismuth selenide (${\mathrm{Bi}}_2{\mathrm{Se}}_3$) subjected to intense midinfrared laser fields. We analyze the contributions from the spin-orbit-coupled bulk states and the topological surface bands separately and reveal a major difference in how their harmonic yields depend on the ellipticity of the laser field. Bulk harmonics show a monotonic decrease in their yield as the ellipticity increases, in a manner reminiscent of high harmonic generation in gaseous media. However, the surface contribution exhibits a highly nontrivial dependence, culminating with a maximum for circularly polarized fields. We attribute the observed anomalous behavior to (i) the enhanced amplitude and the circular pattern of the interband dipole and the Berry connections in the vicinity of the Dirac point and (ii) the influence of the higher-order, hexagonal warping terms in the Hamiltonian, which are responsible for the hexagonal deformation of the energy surface at higher momenta. The latter are associated directly with spin-orbit-coupling parameters. Our results thus establish the sensitivity of strong-field-driven high harmonic emission to the topology of the band structure as well as to the manifestations of spin-orbit interaction.

We show how quantum many-body systems on hyperbolic lattices with nearest-neighbor hopping and local interactions can be mapped onto quantum field theories in continuous negatively curved space. The underlying lattices have recently been realized experimentally with superconducting resonators and therefore allow for a table-top quantum simulation of quantum physics in curved background. Our mapping provides a computational tool to determine observables of the discrete system even for large lattices, where exact diagonalization fails. As an application and proof of principle we quantitatively reproduce the ground state energy, spectral gap, and correlation functions of the noninteracting lattice system by means of analytic formulas on the Poincaré disk, and show how conformal symmetry emerges for large lattices. This sets the stage for studying interactions and disorder on hyperbolic graphs in the future. Importantly, our analysis reveals that even relatively small discrete hyperbolic lattices emulate the continuous geometry of negatively curved space, and thus can be used to experimentally resolve fundamental open problems at the interface of interacting many-body systems, quantum field theory in curved space, and quantum gravity.

We present a kinetic model for optical pumping in ${\mathrm{Lu}}^{+}$ and ${\mathrm{Lr}}^{+}$ ions as well as a theoretical approach to calculate the transport properties of ${\mathrm{Lu}}^{+}$ in its ground ${}^{1}S_0$ and metastable ${}^{3}D_1$ states in helium background gas. Calculations of the initial ion state populations, the field and temperature dependence of the mobilities and diffusion coefficients, and the ion arrival time distributions demonstrate that the ground- and metastable-state ions can be collected and discriminated efficiently under realistic macroscopic conditions.

Established techniques for deterministically creating dark solitons in repulsively interacting atomic Bose-Einstein condensates (BECs) can only access a narrow range of soliton velocities. Because velocity affects the stability of individual solitons and the properties of soliton-soliton interactions, this technical limitation has hindered experimental progress. Here we create dark solitons in highly anisotropic cigar-shaped BECs with arbitrary position and velocity by simultaneously engineering the amplitude and phase of the condensate wave function, improving upon previous techniques which explicitly manipulated only the condensate phase. The single dark soliton solution present in true one-dimensional (1D) systems corresponds to the kink soliton in anisotropic three-dimensional systems and is joined by a host of additional dark solitons, including vortex ring and solitonic vortex solutions. We readily create dark solitons with speeds from zero to half the sound speed. The observed soliton oscillation frequency suggests that we imprinted solitonic vortices, which for our cigar-shaped system are the only stable solitons expected for these velocities. Our numerical simulations of 1D BECs show this technique to be equally effective for creating kink solitons when they are stable. We demonstrate the utility of this technique by deterministically colliding dark solitons with domain walls in two-component spinor BECs.

Here we present an expanded analysis of a model for the manipulation and control of observables in a strongly correlated, many-body system, which was first presented by McCaul et al. [G. McCaul et al., Phys. Rev. Lett. 124, 183201 (2020)]. A field-free, nonlinear equation of motion for controlling the expectation value of an essentially arbitrary observable is derived, together with rigorous constraints that determine the limits of controllability. We show that these constraints arise from the physically reasonable assumptions that the system will undergo unitary time evolution, and has enough degrees of freedom for the electrons to be mobile. Furthermore, we give examples of multiple solutions to generating target observable trajectories when the constraints are violated. Ehrenfest theorems are used to further refine the model and provide a check on the validity of numerical simulations. Finally, the experimental feasibility of implementing the control fields generated by this model is discussed.

We propose and demonstrate a method to increase the momentum separation between the arms of an atom interferometer and thus its area and measurement precision, by using Bloch oscillations (BOs) in an excited band of a pulsed optical standing-wave lattice. Using excited bands allows us to operate at particular “magic” depths, where high momentum-transfer efficiency ($>99.4\%$ per $\hslash k$, where $\hslash k$ is the photon momentum) is maintained while minimizing the lattice-induced phase fluctuations ($<1\mathrm{mrad}$ per $\hslash k$) that are unavoidable in ground-band BOs. We apply this method to demonstrate interferometry with up to $40\hslash k$ momenta supplied by BOs. We discuss extensions of this technique to larger momentum transfer and adaptations towards metrological applications of atom interferometry such as a measurement of the fine-structure constant.

Signatures of quantum transport are expected to quickly vanish as dissipation is introduced in a system. This dissipation can take several forms, including that of particle loss, which has the consequence that the total probability current is not conserved. Here, we study the effect of such losses at a quantum point contact (QPC) for ultracold atoms. Experimentally, dissipation is provided by a near-resonant optical tweezer the power and detuning of which control the loss rates for the different internal atomic states as well as their effective Zeeman shifts. We theoretically model this situation by including losses in the Landauer-Büttiker formalism over a wide range of dissipative rates. We find good agreement between our measurements and our model, both featuring robust conductance plateaus. Finally, we are able to map out the atomic density by varying the position of the near-resonant tweezer inside the QPC, realizing a dissipative scanning gate microscope for cold atoms.

We consider a nanoparticle levitated in a Paul trap in ultrahigh cryogenic vacuum, and look for the conditions which allow for a stringent noninterferometric test of spontaneous collapse models. In particular we compare different possible techniques to detect the particle motion. Key conditions which need to be achieved are extremely low residual pressure and the ability to detect the particle at ultralow power. We compare three different detection approaches based, respectively, on an optical cavity, an optical tweezer, and an electrical readout, and for each one we assess advantages, drawbacks, and technical challenges.

We have measured the quadratic Zeeman coefficient for the ${}^{1}S_0\leftrightarrow {}^{3}P_0$ optical clock transition in ${}^{27}\mathrm{Al}^{+}$, $C_2=-71.944\left(24\right)\mathrm{MHz}/{\mathrm{T}}^2$, and the unperturbed hyperfine splitting of the ${}^{25}\mathrm{Mg}^{+}{}^{2}S_{1/2}$ ground electronic state, $\mathrm{\Delta }W/h=1788762752.85\left(13\right)\mathrm{Hz}$, with improved uncertainties. Both constants are relevant to the evaluation of the ${}^{27}\mathrm{Al}^{+}$ quantum-logic clock systematic uncertainty. The measurement of $C_2$ is in agreement with a previous measurement and a recent calculation at the $1\sigma$ level. The measurement of $\mathrm{\Delta }W$ is in good agreement with a recent measurement and differs from a previously published result by approximately $2\sigma$. With the improved value for $\mathrm{\Delta }W$, we deduce an improved value for the nuclear-to-electronic $g$-factor ratio $g_I/g_J=9.299308313\left(60\right)\times {10}^{-5}$ and the nuclear $g$-factor for the ${}^{25}\mathrm{Mg}$ nucleus $g_I=1.86195782\left(28\right)\times {10}^{-4}$. Using the values of $C_2$ and $\mathrm{\Delta }W$ presented here, we derive a quadratic Zeeman shift of the ${}^{27}\mathrm{Al}^{+}$ quantum-logic clock of $\mathrm{\Delta }\nu /\nu =-(9241.8\pm 3.7)\times {10}^{-19}$, for a bias magnetic field of $B\approx 0.12\mathrm{mT}$.

Optical cavities can induce photon-mediated interactions among intracavity-trapped atoms. Multimode cavities provide the ability to tune the form of these interactions, e.g., by inducing a nonlocal sign-changing term to the interaction. By accounting for the Gouy phase shifts of the modes in a nearly degenerate, confocal, Fabry-Pérot cavity, we provide a theoretical description of this interaction, along with additional experimental confirmation to complement that presented in the companion paper [Y. Guo et al., Phys. Rev. Lett. 122, 193601 (2019)]. Furthermore, we show that this interaction should be written in terms of a complex order parameter, allowing for a $\mathrm{U}\left(1\right)$ symmetry to emerge. This symmetry corresponds to the phase of the atomic density wave arising from self-organization when the cavity is transversely pumped above a critical threshold power. We show theoretically and experimentally how this phase depends on the position of the Bose-Einstein condensate within the cavity and discuss mechanisms that break the $\mathrm{U}\left(1\right)$ symmetry and lock this phase. We then consider alternative Fabry-Pérot multimode cavity geometries (i.e., beyond the confocal) and schemes with more than one pump laser and show that these provide additional capabilities for tuning the cavity-meditated interaction among atoms, including the ability to restore the $\mathrm{U}\left(1\right)$ symmetry despite the presence of symmetry-breaking effects. These photon-mediated interactions may be exploited for realizing quantum liquid crystalline states and spin glasses using multimode optical cavities.

We propose a method for the detection and characterization of nuclear decay processes. Specifically, we describe how nuclear decay recoil can be observed within small particles levitated in an optical trap with high positional resolution. Precise measurements of the magnitude of each recoil as well as their rate of occurrence can provide accurate information about the isotopic composition of a radioactive sample. We expect that this technique for nuclear material characterization will be especially useful in the area of nuclear forensic analysis.

At ultralow energies, atoms and molecules undergo collisions and reactions that are best described in terms of quantum-mechanical wave functions. In contrast, at higher energies these processes can be understood quasiclassically. Here, we investigate the crossover from the quantum-mechanical to the quasiclassical regime both experimentally and theoretically for photodissociation of ultracold diatomic strontium molecules. This basic reaction is carried out with a full control of quantum states for the molecules and their photofragments. The photofragment angular distributions are imaged and calculated by using a quantum-mechanical model as well as the Wenzel–Kramers–Brillouin approximation and a semiclassical approximation that are explicitly compared across a range of photofragment energies. The reaction process is shown to converge to its high-energy (axial-recoil) limit when the energy exceeds the height of any reaction barriers. This phenomenon is quantitatively investigated for two-channel photodissociation by using intuitive parameters for the channel amplitude and phase. While the axial-recoil limit is generally found to be well described by a commonly used quasiclassical model, we find that when the photofragments are identical particles, their bosonic or fermionic quantum statistics can cause this model to fail, requiring a quantum-mechanical treatment even at high energies.