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arXiv:2512.24374

Assembling a Bose-Hubbard superfluid from tweezer-controlled single atoms

William J. Eckner, Theodor Lukin Yelin, Alec Cao, Aaron W. Young, Nelson Darkwah Oppong, Lode Pollet, Adam M. Kaufman

cond-mat.quant-gasphysics.atom-phquant-phSubmitted Dec 30, 2025• Announced Dec 31, 2025• 0 citations
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Abstract

Quantum simulation relies on the preparation and control of low-entropy many-body systems to reveal the behavior of classically intractable models. The development of new approaches for realizing such systems therefore represents a frontier in quantum science. Here we experimentally demonstrate a new protocol for generating ultracold, itinerant many-body states in a tunnel-coupled two-dimensional optical lattice. We do this by adiabatically connecting a near-ground-state-cooled array of up to 50 single strontium-86 atoms with a Bose-Hubbard superfluid. Through comparison with finite-temperature quantum-Monte-Carlo calculations, we estimate that the entropy per particle of the prepared many-body states is approximately $2 k_B$, and that the achieved temperatures are consistent with a significant superfluid fraction. This represents the first time that itinerant many-body systems have been prepared from rearranged atoms, opening the door to bottom-up assembly of a wide range of neutral-atom and molecular systems.

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Quantum simulation relies on the preparation and control of low-entropy many-body systems to reveal the behavior of classically intractable models. The development of new approaches for realizing such systems therefore represents a frontier in quantum science. Here we experimentally demonstrate a new protocol for generating ultracold, itinerant many-body states in a tunnel-coupled two-dimensional optical lattice. We do this by adiabatically connecting a near-ground-state-cooled array of up to 50 single strontium-86 atoms with a Bose-Hubbard superfluid. Through comparison with finite-temperature quantum-Monte-Carlo calculations, we estimate that the entropy per particle of the prepared many-body states is approximately 2kB2 k_B2kB​, and that the achieved temperatures are consistent with a significant superfluid fraction. This represents the first time that itinerant many-body systems have been prepared from rearranged atoms, opening the door to bottom-up assembly of a wide range of neutral-atom and molecular systems.
The preparation of low-entropy starting conditions is a key requirement for many experiments involving neutral atoms. Here we propose a method to autonomously assemble arbitrary spatial configurations of atoms within arrays of optical tweezers or lattice sites, enabled by a combination of tunneling and ground-state laser cooling. In contrast to previous methods, our protocol does not rely on either imaging or evaporative cooling. This circumvents limitations associated with imaging fidelity and loss, especially in systems with small spatial scales, while providing a substantial improvement in speed relative to evaporative approaches. These features may make it well suited for preparing arbitrary initial conditions for Bose-Hubbard or Rydberg interacting systems.
We present a joint experimental and theoretical analysis to assess the adiabatic experimental preparation of ultracold bosons in optical lattices aimed at simulating the three-dimensional Bose-Hubbard model. Thermometry of lattice gases is realized from the superfluid to the Mott regime by combining the measurement of three-dimensional momentum-space densities with ab initio quantum Monte Carlo (QMC) calculations of the same quantity. The measured temperatures are in agreement with isentropic lines reconstructed via QMC for the experimental parameters of interest, with a conserved entropy per particle of S/N=0.8(1)k_{B}. In addition, the Fisher information associated with this thermometry method shows that the latter is most accurate in the critical regime close to the Mott transition, as confirmed in the experiment. These results prove that equilibrium states of the Bose-Hubbard model-including those in the quantum-critical regime above the Mott transition-can be adiabatically prepared in cold-atom apparatus.
We present a platform for the bottom-up construction of itinerant many-body systems: ultracold atoms transferred from a Bose-Einstein condensate into freely configurable arrays of microlens generated focused-beam dipole traps. This complements traditional optical lattices and provides a different access to the field of two-dimensional quantum simulators. The ultimate control of topology, well depth, atom number, and interaction strength is matched by sufficient tunneling. We characterize the required light fields, derive the Bose-Hubbard parameters for several alkali-metal species, and investigate the loading procedures and heating mechanisms. To demonstrate the potential of this approach, we analyze coupled annular Josephson contacts exhibiting many-body resonances.
The ability to control particles in the quantum regime at the individual particle level is a challenge at the frontier of quantum science and engineering. Of the many quantum objects developed in pursuit of this goal, ultracold molecules host rich internal states and unique inter-particle interactions that could lend themselves useful to a broad range of applications including quantum computing and simulation, precision measurements and quantum chemistry. In this thesis we present a bottom-up approach to creating single molecules in individual optical tweezers. In particular, single atoms of two different species are first trapped and cooled in individual optical tweezers then brought together to form a single molecule coherently. Using this approach, we have successfully created an array of fully quantum-state-controlled polar molecules. The quantum state – including both internal and external states – of the resulting molecules are known to us, and is the first time single neutral molecules have been under full quantum state control. This platform offers exciting new opportunities to harness the rich properties of molecules in many quantum science applications.
Ultracold atoms in optical lattices are a powerful platform for the study of quantum many-body physics. The combination of a high degree of isolation from the environment and external control over all relevant parameters makes these systems ideal candidates for the quantum simulation of fundamental lattice models. However, since the atoms are trapped in standing waves of interfering laser beams, the available trap geometries are constrained to regular lattices and single-site control is limited. In this thesis, an alternative experimental platform is investigated. Here, the combination of a microlens array and a spatial light modulator is used to provide a two-dimensional optical microtrap array for ultracold atoms. This setup allows for versatile trap geometries and comprehensive single-site control. The experimental feasibility of the described platform is investigated in the following way. First, the light field generating the microtrap array is simulated using a detailed model of the optical setup. The computed intensity distribution is proportional to the optical dipole potential for the atoms. Second, the simulation results are used to obtain the Hubbard parameters for multiple alkalies from numerical calculations as well as approximative analytical methods. It is shown that the strongly correlated regimes of the Bose-Hubbard model can be reached at sufficiently large tunneling rates. In addition, the impact of fluctuations in the trap parameters is investigated. Third, two approaches are considered for the preparation of low-entropy many-body states. On the one hand, a loading scheme is investigated which starts from a Bose-Einstein condensate and is used in optical lattice experiments. Here, the depth of the microtrap array is increased adiabatically. On the other hand, an array of isolated traps, which is initialized with one atom per site in the respective motional ground state, is considered as starting point. The itinerant regime of the Hubbard model is accessed by an adiabatic decrease of the trap depth. An analysis of ramp-induced excitations and external heating processes shows the feasibility of both approaches. Demonstrating the potential of the investigated platform, two applications are described. On the one hand, the tunneling dynamics of ultracold atoms between weakly coupled ring lattices is analyzed. Controlled by the interaction strength, multiple phenomena can be observed: Josephson oscillations exhibiting collapse and revival, inter-action-induced self-trapping, and tunneling resonances. On the other hand, the implementation of a scheme for universal quantum computing based on time-continuous quantum walks of interacting particles is proposed. Here, the information is encoded into the position of atomic wave packets moving through a planar graph which is built from optical microtraps and implements a quantum circuit. Details of an experimental implementation are discussed for both applications using the results derived in the preceding parts of this thesis.
Ultracold fermionic atoms in optical lattices offer pristine realizations of Hubbard models1, which are fundamental to modern condensed-matter physics2,3. Despite notable advancements4–6, the accessible temperatures in these optical lattice material analogues are still too high to address many open problems7–10. Here we demonstrate a several-fold reduction in temperature6,11–13, bringing large-scale quantum simulations of the Hubbard model into an entirely new regime. This is accomplished by transforming a low-entropy product state into strongly correlated states of interest via dynamic control of the model parameters14,15, which is extremely challenging to simulate classically10. At half-filling, the long-range antiferromagnetic order is close to saturation, leading to a temperature of T/t=0.05−0.05+0.06T/t=0.0{5}_{-0.05}^{+0.06}T/t=0.05−0.05+0.06​ based on comparisons with numerically exact simulations. Doped away from half-filling, it is exceedingly challenging to realize systematically accurate and predictive numerical simulations9. Importantly, we are able to use quantum simulation to identify a new pathway for achieving similarly low temperatures with doping. This is confirmed by comparing short-range spin correlations to state-of-the-art, but approximate, constrained-path auxiliary-field quantum Monte Carlo simulations16–18. Compared with the cuprates2,19,20, the reported temperatures correspond to a reduction from far above to below room temperature, at which physics such as the pseudogap and stripe phases may be expected3,19,21–24. Our work opens the door to quantum simulations that solve open questions in material science, develop synergies with numerical methods and theoretical studies, and lead to discoveries of new physics8,10. A several-fold reduction in temperature is accomplished using a neutral-atom Hubbard quantum simulator by transforming a low-entropy product state into strongly correlated states of interest via dynamic control of the model parameters.