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arXiv:2305.19119

Mid-circuit qubit measurement and rearrangement in a $^{171}$Yb atomic array

Matthew A. Norcia, William B. Cairncross, Barnes, K., P. Battaglino, Brown, A., M. O. Brown, Kayleigh Cassella, C. -A. Chen, Robin Coxe, Daniel Crow, J. Epstein, C. Griger, A. M. W. Jones, Hyosim Kim, Jonathan M. Kindem, Jonathan P. King, Stanimir Kondov, Krish Kotru, J. Lauigan, M. Li, M. Lu, E. Megidish, Marjanovic, J., Mickey McDonald, Thomas Mittiga, Juan A. Muniz, S. Narayanaswami, C. Nishiguchi, Remy Notermans, T. Paule, Pawlak, K., Peng, L., Albert Ryou, A. Smull, D. T. Stack, M. B. Stone, A. Sucich, Miroslav Urbánek, R. J. M. van de Veerdonk, Zachary Vendeiro, Thomas F. Wilkason, Tsung-Yao Wu, Xin Xie, Zhang, X., Benjamin Bloom

Published May 30, 2023• 11 citations
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Abstract

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 $^{171}$Yb 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.

DOI
10.48550/arxiv.2305.19119

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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.
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Subsystem readout during a quantum process, or mid-circuit measurement, is crucial for error correction in quantum computation, simulation, and metrology. Ideal mid-circuit measurement should be faster than the decoherence of the system, high-fidelity, and nondestructive to the unmeasured qubits. Here, we use a strongly coupled optical cavity to read out the state of a single tweezer-trapped ^{87}Rb atom within a small tweezer array. Measuring either atomic fluorescence or the transmission of light through the cavity, we detect both the presence and the state of an atom in the tweezer, within only tens of microseconds, with state preparation and measurement infidelities of roughly 0.5% and atom loss probabilities of around 1%. Using a two-tweezer system, we find measurement on one atom within the cavity causes no observable hyperfine-state decoherence on a second atom located tens of microns from the cavity volume. This high-fidelity mid-circuit readout method is a substantial step toward quantum error correction in neutral atom arrays.
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.
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{}^{171}\mathrm{Yb}171Yb as a data qubit and an optical clock qubit of bosonic 174Yb{}^{174}\mathrm{Yb}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{}^{174}\mathrm{Yb}174Yb. The Hahn-echo sequence with a 399 nm probe and 556 nm cooling beams for 174Yb{}^{174}\mathrm{Yb}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.
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.
We implement mid-circuit operations in a 48-site array of neutral atoms, enabled by new methods for control of the omg\textit{omg}omg (optical-metastable-ground state qubit) architecture present in 171{}^{171}171Yb. We demonstrate laser-based control of ground, metastable and optical qubits with average single-qubit fidelities of Fg=99.968(3)F_{g} = 99.968(3)Fg​=99.968(3), Fm=99.12(4)F_{m} = 99.12(4)Fm​=99.12(4) and Fo=99.804(8)F_{o} = 99.804(8)Fo​=99.804(8). With state-sensitive shelving between the ground and metastable states, we realize a non-destructive state-detection for 171^{171}171Yb, 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)%1.8(6)\%1.8(6)% on ancilla qubits and 4.5(1.0)%4.5(1.0)\%4.5(1.0)% on data qubits, with the former (latter) uncorrected for 1.0(2)%1.0(2)\%1.0(2)% (2.0(2)%2.0(2)\%2.0(2)%) preparation and measurement error; we observe similar performance for mid-circuit reset operations. The reported realization of the omg\textit{omg}omg architecture and mid-circuit operations are door-opening for many tasks in quantum information science, including quantum error-correction, entanglement generation, and metrology.