Floquet -engineered moiré quasicrystal patterns of ultracold Bose gases in twisted bilayer optical lattices

The Coherent Backscattering (CBS) peak is a well-known interferential signature of weak localization in disordered or chaotic systems. More recently, a second interference feature-the Coherent Forward Scattering (CFS) peak-was predicted to emerge in the regime of strong localization. However, it has never been directly observed. Here we report the direct observation of the CFS peak and demonstrate its dual role as a signature of non-ergodicity and as a probe of symmetries in quantum chaotic systems. Using a shaken rotor model realized with a Bose-Einstein condensate (BEC) of ultracold atoms in a modulated optical lattice, we investigate dynamical localization in momentum space. The CFS peak emerges in the position distribution as a consequence of non-ergodic dynamics, while its growth timescale and width reveal the underlying localization length. By finely tuning the modulation, we control time-reversal and parity symmetries and measure their distinct effects on both CBS and CFS peaks in position space. Our results highlight the strong link of both temporal growth and contrast of the coherent scattering peaks with symmetry and localization. This work opens several perspectives for investigating coherent scattering signatures in a many-body context.

Abstract We present a modular Zeeman slower based on permanent magnets, designed for miniaturized quantum sensor applications like Sr optical lattice clocks. Using a longitudinal magnetic field geometry, the 3D printed system replicates the field profile of traditional solenoid-based Zeeman slowers without power consumption or active cooling. The Zeeman slower achieves comparable performance to solenoidbased designs, with a similar number of Sr atoms loaded into the magneto-optical trap at 461 nm transition. This approach offers a low-cost, low-power solution for portable quantum technologies.

Chemical reactions in a statistical ensemble are conventionally regarded as incoherent processes driven by thermodynamics. In the quantum degenerate regime, where atoms and molecules form coherent matter waves, reactions are theoretically described by nonlinear mixing of matter-wave fields. In this scenario, we expect phase matching between reactants and products, analogous to the mixing of photonic fields in nonlinear optics. Here we report on the observation of phase coherent reaction dynamics of Bose-condensed atoms and molecules near a Feshbach resonance. Using matter-wave diffraction with optical lattices, we verify spatial coherence of both atoms and molecules and observe phase doubling when atomic waves combine into molecular waves, the matter-wave analogue of optical frequency doubling. The diffraction patterns further reveal two-atom entanglement generated during the reaction. Our observations establish phase coherence and entanglement generation as two essential features of "quantum many-body chemistry". Moreover, our work opens a pathway to control of reaction dynamics by manipulation of matter-wave phases.

We present an erratum to our Letter [Opt. Lett.50, 5214 (2025)10.1364/OL.566758] correcting two typographical errors: (1) in the expression for M following Eq. (2), and (2) in the expression for δ following Eq. (3). All the simulations in the original Letter were performed using the correct expressions for M and δ, and therefore this correction does not affect the results and conclusions of the original Letter.

Photonic skyrmions are topological textures that exhibit remarkable resilience to environmental perturbations and support deeply subwavelength features, making them promising candidates for high-resolution microscopy, optical computing devices and ultrahigh-density information encoding. However, in contrast to free-space optical skyrmions, all existing approaches to generate polaritonic field skyrmions are limited by a lack of dynamic tunability. In general, without engineering the phase of the incident light, both their lattice site diameter and total topological charges remain fixed after fabrication. These constraints originate from a shared reliance on wavelength-dependent coupling structures or complex excitation conditions. To overcome these limitations, we introduce the concept of dynamically controllable polaritonic topologies generated by non-local photonic modes. Here we leverage quasi-bound states in the continuum resonances in dielectric metasurfaces to launch hyperbolic phonon polaritons in hexagonal boron nitride that interfere to create highly confined photonic skyrmion lattices with diameters down to 271 nm (λ/25). Thanks to the steep dispersion of hexagonal boron nitride, we can change the excitation frequency to achieve control over the size of individual photonic skyrmions within the same physical resonator structure. In addition, our platform is not limited to one type of topology but can generate optical meron lattices and kπ-twist skyrmions through straightforward variations in resonator shape, providing a feasible path towards skyrmion multiplexing and near-arbitrary topologies. The synergistic integration of resonant metasurfaces with polaritonic topologies has potential applications for nanophotonics, such as topological lasing, nonlinear optics and twistronics, as well as for condensed matter physics, such as Chern insulators and topological edge states.

We investigate the interaction-induced resistivity of ultracold fermions in a three-dimensional optical lattice. In situ observations of transport dynamics enable the determination of real and imaginary resistivity. In the strongly interacting metallic regime, we observe a striking saturation of the current-dissipation rate toward a value that is independent of the interaction strength. This phenomenon is quantitatively captured by a dissipation model that uses a renormalized two-body scattering matrix. We further measure the temperature dependence of resistivity in the strongly interacting limit and discuss the predicted asymptotic high-temperature behavior. Our results provide a clear microscopic understanding of bounded resistivity of low-density metals, thus providing a useful benchmark for studies of strongly correlated atomic and electronic systems.

Novel dynamics and Cooper-pair momentum measurement in Fulde-Ferrell-Larkin-Ovchinnikov superfluids on optical lattices

Modal analysis of optical vortex lattices upon propagation and focusing

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We derive an analog of the Lellouch-Lüscher (LL) relation for few-body bosonic systems, linking few-body scattering loss rates to the energies and widths of the corresponding harmonically trapped few-body states. Three-body numerical simulations show that the LL relation applies across a broad range of interaction strengths and energies and allows the determination of scattering rates within a single partial wave. Our Letter establishes a robust theoretical framework for understanding the role of the finite-volume effect in few-body observables in optical lattice and tweezer experiments, enabling precise determination of multibody scattering rates.

Strongly interacting fermions represent the key constituent of several intriguing phases of matter. However, due to the inherent complexity of these systems, important regimes are still inaccessible. Here, we derive a realistic and flexible setup based on ultracold magnetic lanthanide atoms trapped in a one-dimensional optical lattice. Leveraging their large magnetic moments, we design a fermionic t–J model with independently tunable hopping, spin-spin couplings, and onsite interaction. Through combined analytical and numerical analysis, we uncover a variety of many-body quantum phases–including superconducting and topological states. Crucially, in the regime of attractive onsite interaction, we reveal that topology and superconductivity coexist, thus giving rise to an exotic state of matter: a topological triplet superconductor. We also outline a practical protocol to prepare and detect all discovered phases using current experimental techniques. Our results establish an alternative and powerful route for a deeper understanding of strongly interacting fermionic quantum matter.

Abstract We propose a model for tunable $\mathcal{PT}$-symmetric branched optical lattices by investigating both linear and nonlinear Schrödinger equations with a $\mathcal{PT}$-symmetric periodic potential on the graph and solving them by imposing weighted vertex boundary conditions. A constraint derived from these vertex conditions determines the exceptional point of the system. In the $\mathcal{PT}$ unbroken phase, this constraint enforces $\mathcal{PT}$-symmetric boundary conditions at the vertices, ensuring a purely real spectrum; its violation leads to the emergence of complex eigenvalues in the linear regime. In the nonlinear regime, the same constraint determines the linear stability of solitons: satisfying the constraint yields stable solitons, whereas violating it corresponds to unstable solitons.

Quantum simulations of electronic structure and strongly correlated quantum phases are among the most promising applications of quantum computing. These computations benefit from native fermionic encodings1,2, enforcing fermionic statistics and conservation laws such as particle number and magnetization3 independent of gate errors. While ultracold atoms in optical lattices have become established as powerful analogue simulators of strongly correlated fermionic matter4-7, neutral-atom platforms have concurrently emerged as versatile, scalable architectures for spin-based digital quantum computation8. Unifying these capabilities requires high-fidelity motionally coherent gates for fermionic atoms9-11, similar to collisional gates in bosonic systems12,13, paving the way for programmable fermionic quantum processors. Here we demonstrate collisional entangling gates with fidelities up to 99.75(6)% and Bell-state lifetimes exceeding 10 s, realized by means of controlled interactions of fermionic atoms in an optical superlattice. Using quantum gas microscopy14, we microscopically characterize spin-exchange and pair-tunnelling gates and realize a robust composite pair-exchange gate, a key building block for quantum chemistry simulations3,15. Our results establish controlled collisions in optical lattices as a competitive and complementary route to high entangling gate fidelities in neutral-atom quantum computers. Operating intrinsically with fermions, this capability naturally extends to many-qubit architectures, in which fermionic statistics become relevant, enabling complex state preparation and advanced readout16-19 in scalable analogue-digital hybrid quantum simulators. Combined with local addressing20,21, these gates mark a crucial step towards a fully digital fermionic quantum computer based on controlled motion and entanglement of neutral atoms.

Quantum computing represents a central challenge in modern science. Neutral atoms in optical lattices have emerged as a leading computing platform, with collisional gates offering a stable mechanism for quantum logic1-10. However, previous experiments have treated ultracold collisions as a dynamically fine-tuned process11-22, which obscures the underlying quantum geometry and quantum statistics crucial for realizing intrinsically robust operations. Here we propose and experimentally demonstrate a purely geometric two-qubit SWAP gate by transiently populating qubit doublon states of fermionic atoms in a dynamical optical lattice. The presence of these doublon states, together with fermionic exchange anti-symmetry, enables a two-particle quantum holonomy-a geometric evolution in which dynamical phases are absent23. This yields a gate mechanism that is intrinsically protected against fluctuations and inhomogeneities of the confining potentials. The resilience of the gate is further reinforced by time-reversal and chiral symmetries of the Hamiltonian. We experimentally validate this exceptional protection, achieving a loss-corrected amplitude fidelity of 99.91(7)% measured across the entire system consisting of more than 17,000 atom pairs. When combined with recently developed topological pumping methods for atom transport16, our results pave the way for large-scale, highly connected quantum processors. This work introduces a new model for quantum logic that transforms fundamental symmetries, including quantum statistics, into a powerful resource for fault-tolerant computation.

Long-range and multibody interactions are crucial for quantum simulation and quantum computation. Yet, their practical realization using elementary pairwise interactions remains an outstanding challenge. We propose an experimental scheme based on the Bose-Hubbard system with a periodic driving of the on-site energy and global-range density-density interactions, a setup readily implementable via cold atoms in optical lattices with cavity-mediated interactions. Optimally chosen driving parameters can induce global kinetic constraints, where tunneling rates are selectively suppressed depending on the particle number imbalance between all even and odd sites. This mechanism, together with the flexible tunability of local tunneling rates, provides efficient implementation schemes of a family of global controlled gates for quantum computation. We illustrate this scheme for the N-qubit Toffoli gate, circumventing the need for a two-body gate decomposition, and elaborate on the efficient preparation of entangled many-body states.

We introduce and systematically investigate the generation of dispersive shock waves, which arise naturally in physical settings such as optical waveguide arrays and superfluids confined within optical lattices. The underlying physically relevant model is a nonlinear Schrödinger (NLS) equationwith a periodic potential. We consider the evolution of piecewise smooth initial data composed of two distinct nonlinear periodic eigenmodes. To begin interpreting the resulting wave dynamics, we employ the tight-binding approximation, reducing the continuous system to a discrete NLS (DNLS) model with piecewise constant initial data (i.e., a Riemann problem), where each constant state represents a discrete Floquet-Bloch mode at the continuum model level. The resulting tight-binding approximation is shown to display higher fidelity for deeper periodic potentials. This reduced DNLS model effectively models the dynamics at the minima of the periodic potential of the original continuum NLS. Within such a single-band DNLS framework, we apply tools from Whitham modulation theory and long-wave quasicontinuum reductions to uncover and analyze a rich spectrum of nonconvex, discrete dispersive hydrodynamic phenomena, comparing the resulting phenomenology with that of the periodic-potential-bearing continuum model.

We introduce a new class of tunable periodic structures formed by launching two obliquely propagating surface acoustic waves on a piezoelectric substrate that supports a two-dimensional material. The resulting acoustoelectric superlattice exhibits two salient features. First, its periodicity is widely tunable, spanning a length scale intermediate between moiré superlattices and optical lattices, enabling the formation of narrow, topologically nontrivial energy bands. Second, unlike moiré systems, where the superlattice amplitude is set by intrinsic interlayer tunneling and lattice relaxation, the amplitude of the acoustoelectric potential is externally tunable via the surface acoustic wave power. Using massive monolayer graphene as an example, we demonstrate that varying the frequencies and power of the surface acoustic waves enables insitu control over the band structure of the 2D material, generating flat bands and nontrivial valley Chern numbers, featuring a highly localized Berry curvature.

Abstract We report a systematic uncertainty of 9.2×10 -19 for the USTC Sr1 optical lattice clock, achieving accuracy at the level required for the roadmap of the redefinition of the SI second. A finite-element model with in situ -validated, spatially-resolved chamber emissivity reduced blackbody radiation shift uncertainty to 6.3×10 -19 . Concurrently, the externally mounted lattice cavity, by providing a larger beam waist, reduced the atomic density and thereby suppressed the density shift. Enhanced lattice depth modulation consolidated lattice light shift uncertainty to 6.3×10 -19 by enabling simultaneous determination of key polarizabilities and magic wavelength. Magnetic shifts were resolved below 10 -18 via precision characterization of the second-order Zeeman coefficient. Supported by a clock laser stabilized on an ultralow-expansion glass cavity with crystalline-coated mirrors and refined temperature control suppressing BBR fluctuations, the clock also achieves a frequency stability better than 1×10 -18 at 30,000-s averaging time. These developments collectively establish a new benchmark in USTC Sr1 clock performance and pave the way for high-accuracy applications in metrology and fundamental physics.

Abstract Optical Raman lattices in ultra-cold alkali-metal and alkaline-earth atoms provide a powerful method to synthesize spin-orbit (SO) coupling. While the ground-state energy splittings (divided by the Planck’s constant) can reach the range of tens of megahertz in alkali-metal atoms, the typical ground-state energy splittings are on the order of tens of kilohertz or smaller in alkaline-earth atoms (AEAs) such as 87 Sr. For AEAs, because such limited ground-state energy splittings are rather close to the kilohertz-scale recoil energy that is relevant for optical lattice physics, a standard implementation of two-dimensional (2D) optical Raman lattice can lead to parasitic periodic moving potentials that heat up the atomic temperature and severely limit the atomic lifetime. Recently, an improved optical Raman lattice scheme was proposed and experimentally realized in ultra-cold strontium fermions, which significantly enhanced the lifetime of 2D-SO-coupled fermions. However, a concrete electro-optical setup has yet to be demonstrated and its control precision needs to be quantified. Here we demonstrate the electro-optical setup of an improved optical Raman lattice scheme that suppresses the effect of moving lattice potentials for alkaline-earth fermions by introducing a sufficiently large frequency separation between two sets of laser polarization components, where each set yields an independent Raman coupling. To quantify the precision of this setup, we feedback-control the relative phase between two sets of Raman couplings, which is an important parameter characterizing the 1D-2D crossover of SO couplings, and measure the stability of this phase over hour-long periods. We also investigate the optimum range for the applied frequency separation. Our approach provides a useful tool that helps achieve long-lived SO-coupled systems using AEAs.