"The competition of different length scales in quantum many-body systems leads to phenomena such as correlated dynamics and nonlocal order. To investigate such effects in an itinerant lattice-based quantum simulator, it has been proposed to introduce tunable extended-range interactions using off-resonant optical coupling to Rydberg states, known as Rydberg dressing. In this work, we use this approach to realize an effective one-dimensional extended Bose-Hubbard model. Harnessing our quantum gas microscope, we probe the correlated out-of-equilibrium dynamics of extended-range repulsively bound pairs and ""hard rods."" By contrast, operating near equilibrium, we observe density ordering when adiabatically turning on the extended-range interactions. Our results pave the way to realizing light-controlled extended-range interacting quantum many-body systems."

Hybrid systems of single, trapped ions embedded in quantum gases are a promising platform for quantum simulations and the study of long-range interactions in the ultracold regime. Feshbach resonances allow for experimental control over the character and strength of the atom-ion interaction. However, the complexity of atom-ion Feshbach spectra, e.g., due to second-order spin-orbit coupling, requires a detailed experimental understanding of the resonance properties-such as the contributing open-channel partial waves. In this work, we immerse a single barium (Ba & thorn,.) ion in a bath of lithium (Li) atoms spin polarized in their hyperfine ground state to investigate the collision energy dependence of magnetically tunable atom- ion Feshbach resonances. We demonstrate fine control over the kinetic energy of the Ba & thorn,. ion and employ it to explore three-body recombination in the transition from the many- to the few-partial wave regime, marked by a sudden increase of resonant loss. In a dense spectrum-with on average 0.58(1) resonances per Gauss-we select a narrow, isolated feature and characterize it as an s-wave resonance. We introduce a quantum recombination model that allows us to distinguish it from higher-partial-wave resonances. Furthermore, in a magnetic field range with no significant loss at the lowest collision energies, we identify a higher-partial-wave resonance that appears and peaks only when we increase the energy to around the s-wave limit. Our results demonstrate that hybrid atom-ion traps can reach collision energies well in the ultracold regime and that the ion's kinetic energy can be employed to tune the collisional complex to resonance, paving the way for fast control over the interaction in settings where magnetic field variations are detrimental to coherence.

Hybrid atom-ion systems are a rich and powerful platform for studying chemical reactions, asthey feature both excellent control over the electronic state preparation and readout as well as aversatile tunability over the scattering energy, ranging from the few-partial wave regime to the quantum regime. In this work, we make use of these excellent control knobs, and present a joint experimental and theoretical study of the collisions of a single138Ba+ion prepared in the5d2D3/2,5/2metastable states with a ground state6Li gas near quantum degeneracy. We showthat in contrast to previously reported atom-ion mixtures, several non-radiative processes,including charge exchange, excitation exchange and quenching, compete with each other due tothe inherent complexity of the ion-atom molecular structure. We present a full quantum modelbased on high-level electronic structure calculations involving spin-orbit couplings. Results are in excellent agreement with observations, highlighting the strong coupling between the internalangular momenta and the mechanical rotation of the colliding pair, which is relevant in anyother hybrid system composed of an alkali-metal atom and an alkaline-earth ion

The relaxation behaviour of isolated quantum systems taken out of equilibrium is among the most intriguing questions in many-body physics1. Quantum systems out of equilibrium typically relax to thermal equilibrium states by scrambling local information and building up entanglement entropy. However, kinetic constraints in the Hamiltonian can lead to a breakdown of this fundamental paradigm owing to a fragmentation of the underlying Hilbert space into dynamically decoupled subsectors in which thermalization can be strongly suppressed2-5. Here we experimentally observe Hilbert space fragmentation in a two-dimensional tilted Bose-Hubbard model. Using quantum gas microscopy, we engineer a wide variety of initial states and find a rich set of manifestations of Hilbert space fragmentation involving bulk states, interfaces and defects, that is, two-, one- and zero-dimensional objects. Specifically, uniform initial states with equal particle number and energy differ strikingly in their relaxation dynamics. Inserting controlled defects on top of a global, non-thermalizing chequerboard state, we observe highly anisotropic, subdimensional dynamics, an immediate signature of their fractonic nature6-9. An interface between localized and thermalizing states in turn shows dynamics depending on its orientation. Our results mark the observation of Hilbert space fragmentation beyond one dimension, as well as the concomitant direct observation of fractons, and pave the way for in-depth studies of microscopic transport phenomena in constrained systems. Using quantum gas microscopy, Hilbert space fragmentation and fractonic excitations are observed in a two-dimensional tilted Bose-Hubbard model.

The coupling of an isolated quantum state to a continuum is typically associated with decoherence and decreased lifetime. For coupling rates larger than the bandwidth of the associated continuum, decoherence can be mitigated, and new stable eigenstates emerge. Here, we laser-couple diatomic molecules of highly excited Rydberg atoms, so-called Rydberg macrodimers, to a continuum of free motional states. Enabled by their small vibrational eigenfrequencies, we achieve the regime of strong continuum couplings and observe the appearance of new resonances. We explain the observed spectroscopic features as molecular states emerging in the presence of the light field using a Fano model. For atoms arranged on a lattice, we predict the strong continuum coupling to even stabilize triatomic molecules and find the first signatures of these by observing three-atom loss correlations using quantum gas microscopy. Our results present a mechanism to control decoherence and bind polyatomic molecules using strong light-matter interactions.