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arXiv:2305.19266

Mid-circuit operations using the omg-architecture in neutral atom arrays

Joanna W. Lis, Aruku Senoo, William F. McGrew, Felix Rönchen, Alec Jenkins, Adam M. Kaufman

Published May 30, 2023• 14 citations
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Abstract

We implement mid-circuit operations in a 48-site array of neutral atoms, enabled by new methods for control of the $\textit{omg}$ (optical-metastable-ground state qubit) architecture present in ${}^{171}$Yb. We demonstrate laser-based control of ground, metastable and optical qubits with average single-qubit fidelities of $F_{g} = 99.968(3)$, $F_{m} = 99.12(4)$ and $F_{o} = 99.804(8)$. With state-sensitive shelving between the ground and metastable states, we realize a non-destructive state-detection for $^{171}$Yb, and reinitialize in the ground state with either global control or local feed-forward operations. We use local addressing of the optical clock transition to perform mid-circuit operations, including measurement, spin reset, and motional reset in the form of ground-state cooling. In characterizing mid-circuit measurement on ground-state qubits, we observe raw errors of $1.8(6)\%$ on ancilla qubits and $4.5(1.0)\%$ on data qubits, with the former (latter) uncorrected for $1.0(2)\%$ ($2.0(2)\%$) preparation and measurement error; we observe similar performance for mid-circuit reset operations. The reported realization of the $\textit{omg}$ architecture and mid-circuit operations are door-opening for many tasks in quantum information science, including quantum error-correction, entanglement generation, and metrology.

DOI
10.48550/arxiv.2305.19266

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Mid-circuit ground-state cooling and ancilla readout in the omg\textit{omg}omg architecture
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A Dual Metastable-State Encoding Architecture for Quantum Processing with 171Yb^{171}\mathrm{Yb}171Yb Atom Arrays
Neutral-atom arrays combine scalable qubit registers, long coherence times, flexible optical control, and strong Rydberg-mediated entangling interactions, making them a promising platform for quantum information processing. However, physical error rates remain a challenge, and fault-tolerant quantum error correction (QEC) requires repeated mid-circuit measurement and reset of ancilla qubits without disturbing nearby data qubits. This requirement introduces significant control and architectural overhead, making qubit encoding an important architectural decision. Here, we propose a dual metastable-state qubit encoding for 171Yb^{171}\mathrm{Yb}171Yb atoms that utilizes two independent qubit subspaces in the (6s6p) 3P0(6s6p)\,{}^3\mathrm{P}_0(6s6p)3P0​ and (6s6p) 3P2(6s6p)\,{}^3\mathrm{P}_2(6s6p)3P2​ manifolds. The 3P0{}^3\mathrm{P}_03P0​ manifold provides a long-coherence nuclear-spin (NS) qubit suitable for storage and arithmetic operations, while the 3P2{}^3\mathrm{P}_23P2​ manifold provides a hyperfine-spin (HF) qubit, with ΔHF=2π×6.7 GHzΔ_{\mathrm{HF}} = 2π\times 6.7~\mathrm{GHz}ΔHF​=2π×6.7 GHz, that enables fast Raman operations and direct state-selective imaging. Coherent shelving between the two metastable manifolds connects the qubit subspaces, allowing operations to be assigned to spectrally distinct processor zones. We simulate single-qubit and two-qubit gate fidelities in 3P2{}^3\mathrm{P}_23P2​, as well as coherent shelving between the HF and NS qubit subspaces. We incorporate these physical-level estimates into an architectural resource estimation and logical-level simulation. Our approach integrates mid-circuit measurements and fast qubit operations within a single-species platform, providing a versatile framework for future fault-tolerant quantum computing with neutral-atom qubits.
Mid-circuit qubit measurement and rearrangement in a 171^{171}171Yb atomic array
Measurement-based quantum error correction relies on the ability to determine the state of a subset of qubits (ancillae) within a processor without revealing or disturbing the state of the remaining qubits. Among neutral-atom based platforms, a scalable, high-fidelity approach to mid-circuit measurement that retains the ancilla qubits in a state suitable for future operations has not yet been demonstrated. In this work, we perform imaging using a narrow-linewidth transition in an array of tweezer-confined 171^{171}171Yb atoms to demonstrate nondestructive state-selective and site-selective detection. By applying site-specific light shifts, selected atoms within the array can be hidden from imaging light, which allows a subset of qubits to be measured while causing only percent-level errors on the remaining qubits. As a proof-of-principle demonstration of conditional operations based on the results of the mid-circuit measurements, and of our ability to reuse ancilla qubits, we perform conditional refilling of ancilla sites to correct for occasional atom loss, while maintaining the coherence of data qubits. Looking towards true continuous operation, we demonstrate loading of a magneto-optical trap with a minimal degree of qubit decoherence.
The realization of fault-tolerant quantum computation hinges on the ability to execute deep quantum circuits while maintaining gate fidelities consistently above error-correction thresholds. Although neutral-atom arrays have recently demonstrated high-fidelity two-qubit gates and early-stage logical quantum processors, sustaining such high performance across deep, repetitive circuits remains a formidable challenge due to cumulative motional heating and atom loss. Here we demonstrate a sustainable neutral-atom framework that overcomes these limitations by integrating a suite of hardware-efficient mid-circuit operations. We report a two-qubit controlled logic gate with a raw fidelity of 99.60(1)%, which is further increased to a fidelity of 99.81(1)% via non-destructive erasure detection. Crucially, by implementing in-circuit Raman sideband cooling and qubit re-initialization, we demonstrate that gate fidelities can be maintained at the ~99.8% level across multiple operational rounds without observable degradation. By actively managing the internal and motional entropy of the system mid-stream, our in-situ refreshable architecture provides a critical pathway for executing the repeated syndrome-extraction cycles required for large-scale, continuous quantum error correction.
Over the past decade, quantum information science has progressed from few-qubit demonstrations to experiments with hundreds of qubits. Neutral atom processors based on individual atoms trapped in arrays of optical tweezers have emerged as a leading candidate due to their inherent scalability and flexible connectivity. Advanced protocols like measurement-based state preparation and quantum error correction, however, require efficient crosstalk-free mid-circuit operations for the readout, reset, and replenishment of a subset of qubits. In typical single-species atom arrays, where all atoms are identical and on-resonance, such operations necessitate complex overheads from single-site addressing, coherent transport, or shielding techniques, to mitigate the qubit decoherence induced from photons scattered by neighboring atoms. To address this challenge of engineering scalable quantum architectures compatible with efficient control techniques, we introduce and implement the first dual-species atom array platform, and explore new dynamics inaccessible in single-species arrays. In this approach, two atomic species are addressed independently due to the spectral separation between their control wavelengths. We engineer two-dimensional arrays from individual rubidium (Rb) and cesium (Cs) atoms in up to 512 optical tweezers, and show that the two species can be independently trapped, cooled, and imaged with state-of-the-art performance metrics. Harnessing this intrinsic crosstalk-free control, we establish the key primitives of mid-circuit readout, real-time processing and feed-forward, and coherent mid-circuit reloading. By integrating these capabilities, we realize in-sequence, real-time correction of correlated phase errors via a spectator qubit protocol. Next, we excite atoms to Rydberg states in the Förster regime, accessing hitherto unobserved enhanced interspecies Rydberg interactions, and program them to implement the first interspecies CNOT gate. We combine this multispecies entanglement with mid-circuit readout to achieve quantum non-demolition measurement of a Rb-qubit using an auxiliary Cs-qubit, circumventing physical qubit transport. Finally, leveraging the two qubit modalities, we present the first experimental demonstration of quantum cellular automata in atom arrays using only global addressing, and prepare a 17-qubit Cs cluster state with Rb-mediated interactions. The dual-species platform and techniques established in this thesis pave the way toward measurement-based algorithms and real-time feedback control in large-scale quantum systems.
Measuring part of a quantum system in the midst of its evolution and acting on the result in real time is essential for numerous quantum information protocols. Neutral-atom arrays are a leading platform for quantum information processing, but their mid-circuit measurement-and-feedforward cycle times have remained slow, typically exceeding 1 ms. Here we demonstrate fast mid-circuit measurement and real-time feedforward in an array of atomic qubits coupled to a high-finesse optical cavity. Local light shifts tune individual data qubits out of resonance with the cavity, shielding their coherence, while a near-resonant probe drives a selected qubit whose emission is collected with Purcell enhancement. Mid-circuit measurements of four qubits with sub percent infidelity reduce the coherence of a fifth unmeasured data qubit by less than 2%. We implement real-time feedforward to correct measurement-induced phase shifts and to realize an adaptive circuit for optimal quantum state discrimination and conditional state preparation. Our approach reduces the measurement-and-feedforward cycle time to below 100 μμμs and establishes optical cavities as a route to fast control of neutral-atom quantum systems.