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arXiv:2411.11708 · PRX Quantum

High-Fidelity Universal Gates in the 171 Yb Ground-State Nuclear-Spin Qubit

Juan A. Muniz, M. B. Stone, D. T. Stack, M. Jaffe, Jonathan M. Kindem, Laura Wadleigh, E. Zalys-Geller, Xiaogang Zhang, C.-A. Chen, Matthew A. Norcia, J. Epstein, E. Halperin, Frederic Hummel, Thomas F. Wilkason, Ming Li, K. Barnes, P. Battaglino, Thomas C. Bohdanowicz, G. Booth, A. Brown, M. O. Brown, William B. Cairncross, Kayleigh Cassella, Robin Coxe, Daniel Crow, M. Feldkamp, C. Griger, A. Heinz, A. M. W. Jones, Hyosub Kim, Jonathan P. King, Krish Kotru, J. Lauigan, Jan Marjanovic, E. Megidish, M. Meredith, Mickey McDonald, R. Morshead, S. Narayanaswami, C. Nishiguchi, T. Paule, Kelly Ann Pawlak, Kristen L. Pudenz, David Rodríguez Pérez, Albert Ryou, Jonathan Simon, A. Smull, Miroslav Urbánek, R. J. M. van de Veerdonk, Zachary Vendeiro, Tsung-Yao Wu, Xin Xie, Benjamin Bloom

Published May 21, 2025• 44 citations

Abstract

Arrays of optically trapped neutral atoms are a promising architecture for the realization of quantum computers. In order to run increasingly complex algorithms, it is advantageous to demonstrate high-fidelity and flexible gates between long-lived and highly coherent qubit states. In this work, we demonstrate a universal high-fidelity gate set with individually controlled and parallel application of single-qubit gates and two-qubit gates operating on the ground-state nuclear-spin qubit in arrays of tweezer-trapped 171 Yb atoms. We utilize the long lifetime, flexible control, and high gate fidelity of our system to characterize native gates using single- and two-qubit Clifford and symmetric subspace randomized-benchmarking circuits with more than 200 controlled- Z () gates applied to one or two pairs of atoms. We measure our two-qubit entangling gate fidelity to be 99.72(3)% (99.40(3)%) with (without) postselection. In addition, we introduce a simple and optimized method for calibration of multiparameter quantum gates. These results represent important milestones toward executing complex and general quantum computation with neutral atoms.

DOI: 10.1103/prxquantum.6.020334

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Neutral atoms in optical tweezer arrays have emerged as a leading platform for quantum information processing. The fidelity of entangling gates mediated by Rydberg interactions has improved rapidly and is increasingly constrained by blackbody-radiation-induced transitions, which shorten Rydberg lifetimes and create contaminant states that can cause correlated errors. Cryogenic environments can suppress these transition rates by more than an order of magnitude. However, realizing a universal gate set in such an environment has remained an outstanding challenge. Here, we demonstrate a universal quantum gate set in a cryogenic

^{133}

Cs atom array, with a single-qubit gate fidelity of 99.970(2)% and a raw two-qubit entangling-gate fidelity of 99.76(8)%, within the range of leading room-temperature implementations. The entangling gate uses direct single-photon coupling between the electronic ground state and a Rydberg

P

state, avoiding scattering and light shifts associated with two-photon coupling. The gate operates at a modest Rabi frequency of

2π\times4.3

MHz. The measured fidelity agrees with our error model dominated by atomic motion, indicating a straightforward route to higher fidelity through improved cooling, while the fundamental error contribution from Rydberg decay is below

3\times10^{-4}

. These results establish a path to entangling-gate fidelities substantially beyond the current state of the art through cryogenic suppression of Rydberg decay, reducing the overhead for fault-tolerant computation.

We report the implementation of universal two- and three-qubit entangling gates on neutral-atom qubits encoded in long-lived hyperfine ground states. The gates are mediated by excitation to strongly interacting Rydberg states and are implemented in parallel on several clusters of atoms in a one-dimensional array of optical tweezers. Specifically, we realize the controlled-phase gate, enacted by a novel, fast protocol involving only global coupling of two qubits to Rydberg states. We benchmark this operation by preparing Bell states with fidelity F≥95.0(2)%, and extract gate fidelity ≥97.4(3)%, averaged across five atom pairs. In addition, we report a proof-of-principle implementation of the three-qubit Toffoli gate, in which two control atoms simultaneously constrain the behavior of one target atom. These experiments demonstrate key ingredients for high-fidelity quantum information processing in a scalable neutral-atom platform.

Quantum computers must achieve large-scale fault-tolerant operation to deliver on their promise of transformational processing power. This will require thousands or millions of high-fidelity quantum gates and similar numbers of qubits. Demonstrations using neutral-atom qubits trapped and manipulated by lasers have shown that this modality can provide high two-qubit gate () fidelities and scalable operation. However, the gates in these demonstrations are driven by lasers that do not resolve individual qubits, with universal computation enabled by physical midcircuit shuttling of the qubits. This relatively slow operation may greatly extend run times for useful large-scale computation. Here, we demonstrate a universal neutral-atom quantum computer with gate rates limited by optical switching times, rather than shuttling, by individually addressing tightly focused laser beams at an array of single atoms. We achieve fidelity of 99.35(4)% and local single-qubit R Z gate fidelity of 99.902(8)% in both cases accounting for leakage out of the computational basis. Moreover, we demonstrate nondestructive readout of alkali-atom qubits with 0.9(3)% loss, which boosts operational speed. This technique also enables us to measure a state-of-the-art fidelity of 99.73(3)% when excluding atom-loss events, which may be mitigated through erasure conversion. Our results represent a critical step toward large-scale fault-tolerant neutral-atom quantum computers that can execute computations on practical timescales.

Quantum systems with more than two levels - so-called qudits - offer increased computational density and reduced circuit complexity compared to qubit-based architectures, but achieving universal and scalable control remains challenging. We propose an all-optical scheme for universal qudit control in trapped neutral atoms in moderate to high magnetic fields, focusing on the fermionic isotope 173Yb (I = 5/2). The strong hyperfine interaction in the 3P1 manifold enables fast and selective Raman transitions between nuclear-spin states in the 1S0 ground-state manifold using a single linearly polarized laser. For each neighboring transition in the qudit manifold, we identify a magic polarization angle that enables coherent, state-selective control while suppressing off-resonant excitations, with operation frequencies exceeding 100 kHz. Combined with phase-shift operations, this provides universal control of the full single-qudit space. We further discuss compatible two-qudit gates based on the Rydberg blockade mechanism, completing a universal gate set, and analyze state-selective readout schemes compatible with the proposed protocol. Our results identify 173Yb as a promising platform for high-fidelity, all-optical qudit-based quantum information processing.