We demonstrate high-fidelity repetitive measurements of nuclear spin qubits in an array of neutral ytterbium-171 ( 171 Yb) atoms.We show that the qubit state can be measured with a spin-flip probability of 0.004(4) for a single tweezer and 0.012(3) averaged over the array.This is accomplished by high cyclicity of one of the nuclear spin qubit states with an optically excited state under a magnetic field of B = 58 G, resulting in a spin-flip probability of approximately 10 -5 per scattered photon during fluorescence readout.The performance improves further as ∼ 1/B 2 .The state discrimination fidelity is 0.993(4) with a state-averaged readout survival of 0.994(3), limited by off-resonant scattering to dark states.We combine our measurement technique with high-contrast rotations of the nuclear spin qubit via an ac magnetic field to explore two paradigmatic scenarios, including the noncommutativity of measurements in orthogonal bases, and the quantum Zeno mechanism in which measurements "freeze" coherent evolution.Finally, we employ real-time feedforward to repetitively and deterministically prepare the qubit in the +z or -z direction after initializing it in a different basis and performing a measurement in the Z basis.These capabilities constitute an important step towards adaptive quantum circuits with atom arrays.
We demonstrate high-fidelity repetitive measurements of nuclear spin qubits in an array of neutral ytterbium-171 ( 171 Yb) atoms.We show that the qubit state can be measured with a spin-flip probability of 0.004(4) for a single tweezer and 0.012(3) averaged over the array.This is accomplished by high cyclicity of one of the nuclear spin qubit states with an optically excited state under a magnetic field of B = 58 G, resulting in a spin-flip probability of approximately 10 -5 per scattered photon during fluorescence readout.The performance improves further as ∼ 1/B 2 .The state discrimination fidelity is 0.993(4) with a state-averaged readout survival of 0.994(3), limited by off-resonant scattering to dark states.We combine our measurement technique with high-contrast rotations of the nuclear spin qubit via an ac magnetic field to explore two paradigmatic scenarios, including the noncommutativity of measurements in orthogonal bases, and the quantum Zeno mechanism in which measurements "freeze" coherent evolution.Finally, we employ real-time feedforward to repetitively and deterministically prepare the qubit in the +z or -z direction after initializing it in a different basis and performing a measurement in the Z basis.These capabilities constitute an important step towards adaptive quantum circuits with atom arrays.
We report on the realization of a fast, scalable, and high-fidelity qubit architecture, based on 171 Yb atoms in an optical tweezer array.We demonstrate several attractive properties of this atom for its use as a building block of a quantum information processing platform.Its nuclear spin of 1=2 serves as a long-lived and coherent two-level system, while its rich, alkaline-earth-like electronic structure allows for low-entropy preparation, fast qubit control, and high-fidelity readout.We present a near-deterministic loading protocol, which allows us to fill a 10 × 10 tweezer array with 92.73(8)% efficiency and a single tweezer with 96.0(1.4)%efficiency.In the future, this loading protocol will enable efficient and uniform loading of target arrays with high probability, an essential step in quantum simulation and information applications.Employing a robust optical approach, we perform submicrosecond qubit rotations and characterize their fidelity through randomized benchmarking, yielding 5.2ð5Þ × 10 -3 error per Clifford gate.For quantum memory applications, we measure the coherence of our qubits with T Ã 2 ¼ 3.7ð4Þ s and T 2 ¼ 7.9ð4Þ s, many orders of magnitude longer than our qubit rotation pulses.We measure spin depolarization times on the order of tens of seconds and find that this can be increased to the 100 s scale through the application of a several-gauss magnetic field.Finally, we use 3D Raman-sideband cooling to bring the atoms near their motional ground state, which will be central to future implementations of two-qubit gates that benefit from low motional entropy.
While data qubits with a long coherence time are essential for the storage of quantum information, ancilla qubits are pivotal in quantum error correction (QEC) for fault-tolerant quantum computing. The recent development of optical tweezer arrays, such as the preparation of large-scale qubit arrays and high-fidelity gate operations, offers the potential for realizing QEC protocols, and one of the important next challenges is to control and detect ancilla qubits while minimizing atom loss and crosstalk. Here, we present the realization of a hybrid system consisting of a dual-isotope ytterbium (Yb) atom array, in which we can utilize a nuclear spin qubit of fermionic Yb 171 as a data qubit and an optical clock qubit of bosonic Yb 174 as an ancilla qubit with a capacity of nondestructive qubit readout. We evaluate the crosstalk between qubits regarding the impact on the coherence of the nuclear spin qubits from the imaging light for Yb 174 . For the Hahn-echo sequence with a 399 nm probe and 556 nm cooling beams for Yb 174 , we observe 99.1(1.8)% coherence retained under 20 ms exposure, yielding a discrimination fidelity of 0.9992 and a survival probability of 0.988. The Ramsey sequence with a 556 nm probe beam shows negligible influence on the coherence, suggesting the potential future improvement of low crosstalk measurements. This result highlights the potential of the hybrid-Yb atom array for midcircuit measurements for ancilla-qubit-based QEC protocols. Published by the American Physical Society 2024
While data qubits with a long coherence time are essential for the storage of quantum information, ancilla qubits are pivotal in quantum error correction (QEC) for fault-tolerant quantum computing. The recent development of optical tweezer arrays, such as the preparation of large-scale qubit arrays and high-fidelity gate operations, offers the potential for realizing QEC protocols, and one of the important next challenges is to control and detect ancilla qubits while minimizing atom loss and crosstalk. Here, we present the realization of a hybrid system consisting of a dual-isotope ytterbium (Yb) atom array, in which we can utilize a nuclear spin qubit of fermionic 171Yb as a data qubit and an optical clock qubit of bosonic 174Yb as an ancilla qubit with a capacity of non-destructive qubit readout. We evaluate the crosstalk between qubits regarding the impact on the coherence of the nuclear spin qubits from the imaging light for 174Yb. The Hahn-echo sequence with a 399 nm probe and 556 nm cooling beams for 174Yb, we observe 99.1(1.8) % coherence retained under 20 ms exposure, yielding an imaging fidelity of 0.9992 and a survival probability of 0.988. The Ramsey sequence with a 556 nm probe beam shows negligible influence on the coherence, suggesting the potential future improvement of low cross-talk measurements. This result highlights the potential of the hybrid-Yb atom array for ancilla-qubit-based QEC protocols.
Neutral-atom arrays have rapidly advanced to support thousands of qubits and execute high-fidelity logical operations. However, these processors remain severely throttled by their slowest fundamental operation: nondestructive qubit measurement, which requires milliseconds and fundamentally limits the system's clock rate. This bottleneck arises from both an inherent photon-budget dilemma---sufficient fluorescence for reliable state discrimination must be collected without excessive heating or loss---and frame-based imaging, which imposes one common exposure and decision latency on intrinsically independent, site-local measurements. Here, we overcome these limitations with a fast, nondestructive readout architecture based on real-time, site-resolved adaptive protection. By integrating continuous photon counting with a dynamic feedforward framework, we decode qubit states with sub-microsecond latency and instantly shield atoms from redundant scattering. Demonstrated in parallel across a 100-qubit reconfigurable atom array, with adaptive protection on a 25-site subarray, this dynamic decision protocol reduces the average probe time to just 15μs. Model-free benchmarking yields a discrimination infidelity of 4.1×10−5 and an atom loss of 2.1×10−4, simultaneously setting new performance records for atom arrays. Exploiting this capability, we operate repeated quantum circuits at an unprecedented 1.7 kHz clock rate with atoms reused over 120 consecutive rounds---nearly sevenfold higher than the previous record---and enter the sub-millisecond cycle regime for the first time. By removing nondestructive readout as the dominant cycle-time bottleneck, this work unlocks high-clock-rate mid-circuit syndrome extraction, paving the way for high-throughput, fault-tolerant quantum computation.
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.
Neutral atom arrays are a rapidly developing platform for quantum science.Recently, alkaline earth atoms (AEAs) have attracted interest because their unique level structure provides several opportunities for improved performance.In this work, we present the first demonstration of a universal set of quantum gate operations on a nuclear spin qubit in an AEA, using 171 Yb.We implement narrow-line cooling and imaging using a newly discovered magic trapping wavelength at λ ¼ 486.78 nm.We also demonstrate nuclear spin initialization, readout, and single-qubit gates and observe long coherence times [T 1 ≈ 20 s and24ð5Þ s] and a single-qubit operation fidelity F 1Q ¼ 0.99959ð6Þ.We also demonstrate two-qubit entangling gates using the Rydberg blockade, as well as coherent control of these gate operations using light shifts on the Yb þ ion core transition at 369 nm.These results are a significant step toward highly coherent quantum gates in AEA tweezer arrays.