Probing the Kitaev honeycomb model on a neutral-atom quantum computer
Simon J. Evered, Marcin Kalinowski, Alexandra A. Geim, Tom Manovitz, Dolev Bluvstein, Sophie H. Li, Nishad Maskara, Hengyun Zhou, Sepehr Ebadi, Muqing Xu, Joseph Campo, Madelyn Cain, Stefan Ostermann, Susanne F. Yelin, Subir Sachdev A, Markus Greiner, Vladan Vuletić, Mikhail D. Lukin
Quantum simulations of many-body systems are among the most promising applications of quantum computers1. In particular, models based on strongly correlated fermions are central to our understanding of quantum chemistry and materials problems2, and can lead to exotic, topological phases of matter3,4. However, owing to the non-local nature of fermions, such models are challenging to simulate with qubit devices5. Here we realize a digital quantum simulation architecture for two-dimensional fermionic systems based on reconfigurable atom arrays6. We utilize a fermion-to-qubit mapping based on Kitaev’s model on a honeycomb lattice3, in which fermionic statistics are encoded using long-range entangled states7. We prepare these states efficiently using measurement8 and feedforward9, realize subsequent fermionic evolution through Floquet engineering10,11 with tunable entangling gates12 interspersed with atom rearrangement, and improve results with built-in error detection. Leveraging this fermion description of the Kitaev spin model, we efficiently prepare topological states across its complex phase diagram13 and verify the non-Abelian spin-liquid phase3 by evaluating an odd Chern number14,15. We further explore this two-dimensional fermion system by realizing tunable dynamics and directly probing fermion exchange statistics. Finally, we simulate strong interactions and study the dynamics of the Fermi–Hubbard model on a square lattice. These results pave the way for digital quantum simulations of complex fermionic systems for materials science, chemistry16 and high-energy physics17. Digital quantum simulations of Kitaev’s honeycomb model are realized for two-dimensional fermionic systems using a reconfigurable atom-array processor and used to study the Fermi–Hubbard model on a square lattice.
Quantum simulations of many-body systems are among the most promising applications of quantum computers1. In particular, models based on strongly correlated fermions are central to our understanding of quantum chemistry and materials problems2, and can lead to exotic, topological phases of matter3,4. However, owing to the non-local nature of fermions, such models are challenging to simulate with qubit devices5. Here we realize a digital quantum simulation architecture for two-dimensional fermionic systems based on reconfigurable atom arrays6. We utilize a fermion-to-qubit mapping based on Kitaev’s model on a honeycomb lattice3, in which fermionic statistics are encoded using long-range entangled states7. We prepare these states efficiently using measurement8 and feedforward9, realize subsequent fermionic evolution through Floquet engineering10,11 with tunable entangling gates12 interspersed with atom rearrangement, and improve results with built-in error detection. Leveraging this fermion description of the Kitaev spin model, we efficiently prepare topological states across its complex phase diagram13 and verify the non-Abelian spin-liquid phase3 by evaluating an odd Chern number14,15. We further explore this two-dimensional fermion system by realizing tunable dynamics and directly probing fermion exchange statistics. Finally, we simulate strong interactions and study the dynamics of the Fermi–Hubbard model on a square lattice. These results pave the way for digital quantum simulations of complex fermionic systems for materials science, chemistry16 and high-energy physics17. Digital quantum simulations of Kitaev’s honeycomb model are realized for two-dimensional fermionic systems using a reconfigurable atom-array processor and used to study the Fermi–Hubbard model on a square lattice.
Understanding topological matter is an outstanding challenge across several disciplines of physical science.Programmable quantum simulators have emerged as a powerful approach to studying such systems.While quantum spin liquids of paradigmatic toric code type have recently been realized in the laboratory, controlled exploration of topological phases with non-Abelian excitations remains an open problem.We introduce and analyze a new approach to simulating topological matter based on periodic driving.Specifically, we describe a model for a so-called Floquet spin liquid, obtained through a periodic sequence of parallel quantum gate operations that effectively simulates the Hamiltonian of the non-Abelian spin liquid in Kitaev's honeycomb model.We show that this approach, including the toolbox for preparation, control, and readout of topological states, can be efficiently implemented in state-of-the-art experimental platforms.One specific implementation scheme is based on Rydberg atom arrays and utilizes recently demonstrated coherent qubit transport combined with controlled-phase gate operations.We describe methods for probing the non-Abelian excitations, and the associated Majorana zero modes, and simulate possible fusion and braiding experiments.Our analysis demonstrates the potential of programmable quantum simulators for exploring topological phases of matter.Extensions including simulation of Kitaev materials and lattice gauge theories are also discussed.
Quantum processors have the potential to significantly advance our understanding of quantum systems. In particular, the programmability of digital quantum devices enables access to highly tunable quantum dynamics and observables. The central challenge, however, is suppressing errors, making quantum error correction essential for large-scale algorithms. In this thesis, I present work on quantum processing with reconfigurable atom arrays, with experiments featuring up to 448 neutral atom qubits, high two-qubit gate fidelities, arbitrary connectivity, and mid-circuit qubit readout and reuse. Using this system, I describe how we realize gate-based quantum simulations. In particular, we experimentally study Kitaev’s honeycomb model and explore hardware-efficient fermion-to-qubit encodings. We then leverage unique opportunities with atoms to study the key building blocks of scalable quantum error correction. These include below-threshold performance, deep computation at constant entropy, and universal logical gates. Together, these experiments highlight unique near-term opportunities with atom arrays and chart a path toward future large-scale atomic processors.
Kitaev's honeycomb model is a paradigmatic exactly solvable system hosting a quantum spin liquid with non-Abelian anyons and topologically protected edge modes, offering a platform for fault-tolerant quantum computation. However, real candidate Kitaev materials invariably include complex secondary interactions that obscure the realization of spin-liquid behavior and demand novel quantum computational approaches for efficient simulation. Here we report quantum simulations of a 22-site Kitaev honeycomb lattice on a trapped-ion quantum processor, without and with non-integrable Heisenberg interactions that are present in real materials. We develop efficient quantum circuits for ground-state preparation, achieving high accuracy with energy errors equivalent to an effective temperature of 0.2 (in units of the Kitaev interactions), consistent with the experimentally relevant spin-liquid regime. Starting from these states, we apply controlled perturbations and measure time-dependent spin correlations along the system's edge. In the non-Abelian phase, we observe chiral edge dynamics consistent with a non-zero Chern number, a hallmark of topological order, which vanishes upon transition to the Abelian toric code phase. Extending to the non-integrable Kitaev-Heisenberg model, we find that weak Heisenberg interactions preserve chiral edge dynamics, while stronger couplings suppress them, signaling the breakdown of topological protection. Our work demonstrates a viable route for probing dynamical signatures of topological order in quantum spin liquids using programmable quantum hardware, opening new pathways for quantum simulation of strongly correlated materials.
Simulating the properties of many-body fermionic systems is an outstanding computational challenge relevant to material science, quantum chemistry, and particle physics.-5.4pc]Please note that the spelling of the following author names in the manuscript differs from the spelling provided in the article metadata: D. González-Cuadra, D. Bluvstein, M. Kalinowski, R. Kaubruegger, N. Maskara, P. Naldesi, T. V. Zache, A. M. Kaufman, M. D. Lukin, H. Pichler, B. Vermersch, Jun Ye, and P. Zoller. The spelling provided in the manuscript has been retained; please confirm. Although qubit-based quantum computers can potentially tackle this problem more efficiently than classical devices, encoding nonlocal fermionic statistics introduces an overhead in the required resources, limiting their applicability on near-term architectures. In this work, we present a fermionic quantum processor, where fermionic models are locally encoded in a fermionic register and simulated in a hardware-efficient manner using fermionic gates. We consider in particular fermionic atoms in programmable tweezer arrays and develop different protocols to implement nonlocal gates, guaranteeing Fermi statistics at the hardware level. We use this gate set, together with Rydberg-mediated interaction gates, to find efficient circuit decompositions for digital and variational quantum simulation algorithms, illustrated here for molecular energy estimation. Finally, we consider a combined fermion-qubit architecture, where both the motional and internal degrees of freedom of the atoms are harnessed to efficiently implement quantum phase estimation as well as to simulate lattice gauge theory dynamics.
Abstract 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 encodings 1,2 , enforcing fermionic statistics and conservation laws such as particle number and magnetization 3 independent of gate errors. While ultracold atoms in optical lattices have become established as powerful analogue simulators of strongly correlated fermionic matter 4–7 , neutral-atom platforms have concurrently emerged as versatile, scalable architectures for spin-based digital quantum computation 8 . Unifying these capabilities requires high-fidelity motionally coherent gates for fermionic atoms 9–11 , similar to collisional gates in bosonic systems 12,13 , 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 microscopy 14 , we microscopically characterize spin-exchange and pair-tunnelling gates and realize a robust composite pair-exchange gate, a key building block for quantum chemistry simulations 3,15 . 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 readout 16–19 in scalable analogue–digital hybrid quantum simulators. Combined with local addressing 20,21 , these gates mark a crucial step towards a fully digital fermionic quantum computer based on controlled motion and entanglement of neutral atoms.
Programmable quantum systems provide insights into many-body quantum phenomena and enable new methods for computation and metrology. The frontier challenge for these systems is scaling up in the number of quantum particles while retaining a high degree of quantum control. In recent years arrays of neutral atoms have emerged as a scalable and powerful platform for tackling these challenges, thanks to their large number of qubits, flexible geometry, and a well-established toolbox for preparation, detection, coherent control. At the forefront of quantum science and engineering, these systems have been used for quantum simulation of various spin models and have also demonstrated building blocks of quantum computation. In this thesis I will present advances in development of large two-dimensional atom arrays, where hundreds of individual atoms are trapped, rearranged, and initialized in various defect-free arrangements in one or two dimensions. Afterwards, interactions between atoms is controlled via coherent excitation to highly excited Rydberg states, resulting in strong long-range van der Waals forces. We utilize these interaction for quantum simulation of many-body spin Hamiltonians by demonstrating preparation of several exotic phases of matter, study phase transitions, and probe non-equilibrium dynamics. Further, we study the quantum speedup in solving a hard combinatorial optimization problem via efficiently mapping the problem onto the Rydberg atom array. We also utilize Rydberg interactions to demonstrate high-fidelity two-qubit gate operations in a reconfigurable atom array architecture. Lastly I will demonstrate recent technical improvements that have enabled larger system sizes, higher fidelity rydberg excitations, and local control of individual atoms, paving the way for novel approaches for studying quantum many-body phenomena.