When quantum particles are confined into lower dimensions, an effective three-body interaction inevitably arises and may cause significant consequences. Here we study bosons in one dimension with weak two-body and three-body interactions, predict the existence of two three-body bound states when both interactions are attractive, and determine their binding energies as universal functions of the two-body and three-body scattering lengths. We also show that an infinitesimal three-body attraction induces an excited bound state only for 3, 39, or more bosons. Our findings herein have direct relevance to a broad range of quasi-one-dimensional systems realized with ultracold atoms.

Shallow trimers composed of three bosonic atoms in one-dimensional harmonic waveguides are studied in the vicinity of a Feshbach resonance. It is shown that for arbitrarily large values of the one-dimensional scattering length, an excited trimer branch exists in coexistence with the dimer and the trimer of the Lieb-Liniger model.

We solve the three-boson problem with contact two- and three-body interactions in one dimension and analytically calculate the ground and excited trimer-state energies. Then, by using the diffusion Monte Carlo technique, we calculate the binding energy of three dimers formed in a one-dimensional Bose-Bose or Fermi-Bose mixture with attractive interspecies and repulsive intraspecies interactions. Combining these results with our three-body analytics, we extract the three-dimer scattering length close to the dimer-dimer zero crossing. In both considered cases, the three-dimer interaction turns out to be repulsive. Our results constitute a concrete proposal for obtaining a one-dimensional gas with a pure three-body repulsion.

Experimental observation of the decoherence of macroscopic objects is of fundamental importance to the study of quantum collapse models and the quantum to classical transition. Optomechanics is a promising field for the study of such models because of its fine control and readout of mechanical motion. Nevertheless, it is challenging to monitor a mechanical superposition state for long enough to investigate this transition. We present a scheme for entangling two mechanical resonators in spatial superposition states such that all quantum information is stored in the mechanical resonators. The scheme is general and applies to any optomechanical system with multiple mechanical modes. By analytic and numeric modeling, we show that the scheme is resilient to experimental imperfections such as incomplete precooling, faulty postselection, and inefficient optomechanical coupling. This proposed procedure overcomes limitations of previously proposed schemes that have so far hindered the study of macroscopic quantum dynamics.

The Schrödinger equation for the ground state of the hydrogen molecule ${\mathrm{H}}_2$ is solved by applying the Rayleigh-Ritz variational method in Hylleraas coordinates without using the Born-Oppenheimer approximation. The nonrelativistic energy eigenvalue is converged to $-1.164025030880\left(7\right)$ atomic units. The leading-order relativistic corrections, including the mass-velocity, Darwin, orbit-orbit, spin-spin, and relativistic recoil terms, are evaluated perturbatively. Together with the higher-order relativistic and quantum electrodynamic corrections obtained by Puchalski et al. [Phys. Rev. Lett. 117, 263002 (2016)], we determine the dissociation energy of the hydrogen molecule, $D_0=36118.06971\left(33\right){\mathrm{cm}}^{-1}$, which agrees with the two recent experimental results of Liu et al. [J. Chem. Phys. 130, 174306 (2009)], $36118.06962\left(37\right){\mathrm{cm}}^{-1}$, and Altmann et al. [Phys. Rev. Lett. 120, 043204 (2018)], $36118.06945\left(31\right){\mathrm{cm}}^{-1}$.

A circularly polarized laser beam is used to levitate and control the rotation of microspheres in high vacuum. At low pressure, rotation frequencies as high as 6 MHz are observed for birefringent vaterite spheres, limited by centrifugal stresses. Due to the extremely low damping in high vacuum, the controlled optical rotation of amorphous ${\mathrm{SiO}}_2$ spheres is also observed at rates above several MHz. At ${10}^{-7}$ mbar, a damping time of $6\times {10}^4$ s is measured for a $10\text{−}\mu \mathrm{m}$-diam ${\mathrm{SiO}}_2$ sphere. No additional damping mechanisms are observed above gas damping, indicating that even longer damping times may be possible with operation at lower pressure. The controlled optical rotation of microspheres at MHz frequencies with low damping, including for materials that are not intrinsically birefringent, provides a tool for performing precision measurements using optically levitated systems.

Laser-cooled lanthanide atoms are ideal candidates with which to study strong and unconventional quantum magnetism with exotic phases. Here, we use state-of-the-art closed-coupling simulations to model quantum magnetism for pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical lattice. In contrast to the widely used single-channel Hubbard model description of atoms and molecules in an optical lattice, we focus on the single-site multichannel spin evolution due to spin-dependent contact, anisotropic van der Waals, and dipolar forces. This has allowed us to identify the leading mechanism, orbital anisotropy, that governs molecular spin dynamics among erbium atoms. The large magnetic moment and combined orbital angular momentum of the $4f$-shell electrons are responsible for these strong anisotropic interactions and unconventional quantum magnetism. Multichannel simulations of magnetic Cr atoms under similar trapping conditions show that their spin evolution is controlled by spin-dependent contact interactions that are distinct in nature from the orbital anisotropy in Er. The role of an external magnetic field and the aspect ratio of the lattice site on spin dynamics is also investigated.

A parity-time ($\mathcal{PT}$)-symmetric system emerging from a quantum dynamics is highly desirable in order to understand the possible implications of $\mathcal{PT}$ symmetry in the next generation of quantum technologies. In this work, we address this need by proposing and studying a circuit-QED architecture that consists of two coupled resonators and two qubits (each coupled to one resonator). By means of external driving fields on the qubits, we are able to tune gains and losses in the resonators. Starting with the quantum dynamics of this system, we show the emergence of the $\mathcal{PT}$ symmetry via the selection of both driving amplitudes and frequencies. We engineer the system such that a non-number-conserving dipole-dipole interaction emerges, introducing an instability at large coupling strengths. The $\mathcal{PT}$ symmetry and its breaking, as well as the predicted instability in this circuit-QED system, can be observed in a transmission experiment.

The use of multiparticle entangled states has the potential to drastically increase the sensitivity of atom interferometers and atomic clocks. The twist-and-turn (TNT) Hamiltonian can create multiparticle entanglement much more rapidly than the ubiquitous one-axis twisting Hamiltonian in the same spin system. In this paper, we consider the effects of detection noise—a key limitation in current experiments—on the metrological usefulness of nonclassical states generated under TNT dynamics. We also consider a variety of interaction-based readouts to maximize their performance. Interestingly, the optimum interaction-based readout is not the obvious case of perfect time reversal.

The two-loop self-energy correction to the Lamb shift of hydrogenlike ions is calculated for the $1s$, $2s$, and $2p_{1/2}$ states and nuclear charge numbers $Z=30-100$. The calculation is performed to all orders in the nuclear binding strength parameter $Z\alpha$. As compared to previous calculations of this correction, numerical accuracy is improved by an order of magnitude and the region of the nuclear charges is extended. An analysis of the $Z$ dependence of the obtained results demonstrates their consistency with the known $Z\alpha$-expansion coefficients.

We present a joint experimental and theoretical study of resonant interatomic Coulombic decay (RICD) in HeNe employing high resolution cold target recoil ion momentum spectroscopy and ab initio electronic structure and nuclear dynamics calculations. In particular, laboratory- and molecular-frame angular emission distributions of RICD electrons are examined in detail. The exciting-photon energy-dependent anisotropy parameter $\beta \left(\omega \right)$, measured for decay events that populate bound ${\mathrm{HeNe}}^{+}$ ions, is in agreement with the calculations performed for the ground ionic state $X^2{\mathrm{\Sigma }}_{1/2}^{+}$. A contribution from the $a^2{\mathrm{\Pi }}_{3/2}$ final ionic state is found to be negligible. For the $\mathrm{He}+{\mathrm{Ne}}^{+}$ fragmentation channel, the observed laboratory-frame angular distribution of RICD electrons is explained by a slow homogeneous dissociation of bound vibrational levels of the final ionic state $A^2{\mathrm{\Pi }}_{1/2}$ into vibrational continua of the lower lying states $X^2{\mathrm{\Sigma }}_{1/2}^{+}$ and $a^2{\mathrm{\Pi }}_{3/2}$. Our calculations predict that the angular distributions of RICD electrons in the body-fixed dipole plane provide direct access to the electronic character (i.e., symmetry) of intermediate vibronic resonances. However, because of the very slow dissociation of the $A^2{\mathrm{\Pi }}_{1/2}$ state, the molecular-frame angular distributions of RICD electrons in the $\mathrm{He}+{\mathrm{Ne}}^{+}$ fragmentation channel are inaccessible to our coincidence experiment.

We investigate the physical origin of frequency-modulated combs generated from single-section semiconductor diode lasers based on quantum wells, isolating the essential physics necessary for comb generation. We find that the two effects necessary for comb generation—spatial hole burning (leading to multimode operation) and four-wave mixing (leading to phase locking)—are indeed present in some quantum-well systems. The physics of comb generation in quantum wells is similar to that in quantum dot and quantum cascade lasers. We discuss the nature of the spectral phase and some important material parameters of these diode lasers.

We propose feasible scenarios for revealing the modified exchange statistics in one-dimensional anyon models in optical lattices based on an extension of the multicolor lattice-depth modulation scheme introduced in [Phys. Rev. A 94, 023615 (2016)]. We show that the fast modulation of a two-component fermionic lattice gas in the presence a magnetic field gradient, in combination with additional resonant microwave fields, allows for the quantum simulation of hardcore anyon models with periodic boundary conditions. Such a semisynthetic ring setup allows for realizing an interferometric arrangement sensitive to the anyonic statistics. Moreover, we show as well that simple expansion experiments may reveal the formation of anomalously bound pairs resulting from the anyonic exchange.

The Kochen-Specker theorem rules out models of quantum theory wherein projective measurements are assigned outcomes deterministically and independently of context. This notion of noncontextuality is not applicable to experimental measurements because these are never free of noise and thus never truly projective. For nonprojective measurements, therefore, one must drop the requirement that an outcome be assigned deterministically in the model and merely require that it be assigned a distribution over outcomes in a manner that is context-independent. By demanding context independence in the representation of preparations as well, one obtains a generalized principle of noncontextuality that also supports a quantum no-go theorem. Several recent works have shown how to derive inequalities on experimental data which, if violated, demonstrate the impossibility of finding a generalized-noncontextual model of this data. That is, these inequalities do not presume quantum theory and, in particular, they make sense without requiring an operational analog of the quantum notion of projectiveness. We here describe a technique for deriving such inequalities starting from arbitrary proofs of the Kochen-Specker theorem. It extends significantly previous techniques that worked only for logical proofs, which are based on sets of projective measurements that fail to admit of any deterministic noncontextual assignment, to the case of statistical proofs, which are based on sets of projective measurements that $do$ admit of some deterministic noncontextual assignments, but not enough to explain the quantum statistics.

Spectroscopic tools are fundamental for the understanding of complex quantum systems. Here, we demonstrate high-precision multiband spectroscopy in a graphenelike lattice using ultracold fermionic atoms. From the measured band structure, we characterize the underlying lattice potential with a relative error of $1.2\times {10}^{-3}$. Such a precise characterization of complex lattice potentials is an important step towards precision measurements of quantum many-body systems. Furthermore, we explain the excitation strengths into different bands with a model and experimentally study their dependency on the symmetry of the perturbation operator. This insight suggests the excitation strengths as a suitable observable for interaction effects on the eigenstates.

We show experimentally that three-dimensional laser cooling of lithium atoms on the $D_2$ line is possible when the laser light is tuned exactly to resonance with the dominant atomic transition. Qualitatively, it can be understood by applying simple Doppler cooling arguments to the specific hyperfine structure of the excited state of lithium atoms, which is both dense and inverted. However, to build a quantitative theory, we must resolve to a full model which takes into account both the entire atomic structure of all 24 Zeeman sublevels and the laser light polarization. Moreover, by means of Monte Carlo simulations, we show that coherent processes play an important role in showing consistency between the theory and the experimental results.

We study experimentally various physical limitations and technical imperfections that lead to damping and finite contrast of optically driven Rabi oscillations between ground and Rydberg states of a single atom. Finite contrast is due to preparation and detection errors, and we show how to model and measure them accurately. Part of these errors originates from the finite lifetime of Rydberg states, and we observe its $n^3$ scaling with the principal quantum number $n$. To explain the damping of Rabi oscillations, we use simple numerical models taking into account independently measured experimental imperfections and show that the observed damping actually results from the accumulation of several small effects, each at the level of a few percent. We discuss prospects for improving the coherence of ground-Rydberg Rabi oscillations in view of applications in quantum simulation and quantum information processing with arrays of single Rydberg atoms.

Virialized ultralight fields (VULFs) are viable cold dark-matter candidates and include scalar and pseudoscalar bosonic fields, such as axions and dilatons. Direct searches for VULFs rely on low-energy precision-measurement tools. While previous proposals have focused on detecting coherent oscillations of the VULF signals at the VULF Compton frequencies for individual devices, here I consider a network of such devices. Virialized ultralight fields are essentially dark-matter waves and as such they carry both temporal and spatial phase information. Thereby, the discovery reach can be improved by using networks of precision-measurement tools. To formalize this idea, I derive a spatiotemporal two-point correlation function for the ultralight dark-matter fields in the framework of the standard halo model. Due to VULFs being Gaussian random fields, the derived two-point correlation function fully determines $N$-point correlation functions. For a network of $N_D$ devices within the coherence length of the field, the sensitivity compared to a single device can be improved by a factor of $\sqrt{N_D}$. Further, I derive a VULF dark-matter signal profile for an individual device. The resulting line shape is strongly asymmetric due to the parabolic dispersion relation for massive nonrelativistic bosons. I discuss the aliasing effect that extends the discovery reach to VULF frequencies higher than the experimental sampling rate. I present sensitivity estimates and develop a stochastic field signal-to-noise ratio statistic. Finally, I consider an application of the formalism developed to atomic clocks and their networks.

Photons from distant astronomical sources can be used as a classical source of randomness to improve fundamental tests of quantum nonlocality, wave-particle duality, and local realism through Bell's inequality and delayed-choice quantum eraser tests inspired by Wheeler's cosmic-scale Mach-Zehnder interferometer gedanken experiment. Such sources of random numbers may also be useful for information-theoretic applications such as key distribution for quantum cryptography. Building on the design of an astronomical random number generator developed for the recent cosmic Bell experiment [Handsteiner et al. Phys. Rev. Lett. 118, 060401 (2017)], in this paper we report on the design and characterization of a device that, with 20-nanosecond latency, outputs a bit based on whether the wavelength of an incoming photon is greater than or less than $\approx 700$ nm. Using the one-meter telescope at the Jet Propulsion Laboratory Table Mountain Observatory, we generated random bits from astronomical photons in both color channels from 50 stars of varying color and magnitude, and from 12 quasars with redshifts up to $z=3.9$. With stars, we achieved bit rates of $\sim 1\times {10}^6{\mathrm{Hz}/\mathrm{m}}^2$, limited by saturation of our single-photon detectors, and with quasars of magnitudes between 12.9 and 16, we achieved rates between $\sim {10}^2$ and $2\times {10}^3\mathrm{Hz}/{\mathrm{m}}^2$. For bright quasars, the resulting bitstreams exhibit sufficiently low amounts of statistical predictability as quantified by the mutual information. In addition, a sufficiently high fraction of bits generated are of true astronomical origin in order to address both the locality and freedom-of-choice loopholes when used to set the measurement settings in a test of the Bell-CHSH inequality.

Optical binding is a form of light-mediated forces between elements of matter which emerge in response to the collective scattering of light. Such a phenomenon has been studied mainly in the context of the equilibrium stability of dielectric sphere arrays which move amid dissipative media. In this article, we demonstrate that optically bounded states of a pair of cold atoms can exist, in the absence of nonradiative damping. We study the scaling laws for the unstable-stable phase transition at negative detuning and the unstable-metastable one for positive detuning. In addition, we show that angular momentum can lead to dynamical stabilization with infinite-range scaling.