Error rates fall below 10^(-4) in a new neutral-atom quantum design

Researchers from Fudan University and Shanghai Buchou Quantum Technology Co., Ltd. have achieved error rates to the 10^(-4) level. The team proposes a universal fault-tolerant architecture using globally driven atom arrays, enabling qubit addressability without complex, locally addressed quantum gates. This system constructs a native instruction set called Global Rydberg Atom Instruction Language (GRAIL), and demonstrates a logical error rate below 10^(-9) for magic states, offering a path to simpler control for large-scale quantum computation.

Dual-Species Atom Arrays Enable Fault-Tolerant Control

Crosstalk error suppression to the ${10}^{–4}$ level is achieved by the architecture, a performance benchmark previously difficult to reach in neutral atom quantum designs. This level of control stems from a novel approach using globally driven dual-species atom arrays, enabling qubit addressability without the need for individually targeted quantum gates. GRAIL allows for the compilation of both surface-code error correction and the cultivation of magic states, components important for fault-tolerant quantum computation, while also employing parallelization to further minimize crosstalk.

Beyond simply reducing errors, this system establishes a hardware-inferred circuit-level noise model yielding an error-correction threshold of 1. 43% for quantum memory. This threshold was determined using minimum-weight perfect matching decoding, a technique for identifying and correcting errors in quantum systems. The architecture supports fault-tolerant logical computation through transversal implementations of Hadamard, phase, and CZ gates, alongside non-transversal logical T gates enabled by magic state cultivation.

These components collectively demonstrate a pathway toward universal fault-tolerant quantum computing using the globally driven, dual-species atom array approach. The design fundamentally separates programmable qubit addressability from the complexities of local quantum control, potentially simplifying the scaling of neutral-atom processors. Specifically, the reconfiguration of rubidium arrays eliminates the need for individually calibrated Raman beams targeting cesium sites, a significant reduction in calibration requirements. Global microwave pulses drive high-fidelity single-qubit rotations within the neutral-atom arrays, using the well-separated hyperfine transition frequencies of rubidium and cesium atoms for independent control of each species.

The system uses a notation, s ∈ Rb,Cs,RbCs, to specify which species a global operation targets, providing precise control over the quantum system. “Building on this physical architecture, we introduce the native instructions as follows,” the researchers state, highlighting the integrated nature of the hardware and software components. This architecture offers a route to simpler control for large-scale fault-tolerant neutral-atom computation, potentially accelerating the development of practical quantum computers.

Global Rydberg Atom Instruction Language (GRAIL) for Universal Gates

Suppression of crosstalk errors to below the 10^(-4) level within a neutral-atom quantum system is enabled by the design of a universal instruction set, dubbed Global Rydberg Atom Instruction Language (GRAIL). This architecture achieves qubit addressability through interspecies Rydberg interactions, eliminating the need for locally addressed quantum gates and relying instead on the spatial arrangement of auxiliary atoms. A hybrid system using rubidium and caesium atoms forms the basis of this approach, with one species encoding physical qubits and the other serving as an auxiliary register for operation control and state probing.

The GRAIL instruction set comprises five core families: global single-qubit rotations, atom shuttling, global Rydberg pulses, reset and measurement. Atom shuttling, specifically, uses rubidium atom movement to define pairs within a Rydberg blockade radius, enabling selective application of operations.

This process is defined by the instruction $S{h}_{Rb}(Q)$, where Q represents the disjoint set of atom pairs targeted for interaction. The system’s design exploits the identical internal structure and digital nature of atoms, reducing the need for precise calibration of locally focused optical fields, a common challenge in other quantum computing modalities. The architecture’s ability to apply gates selectively under global driving is central to this fault-tolerance strategy.

Specifically, the controlled-phase gate, CP(Q;φ), is implemented by combining atom shuttling and global Rydberg pulses, ensuring conditional phase acquisition only by caesium atoms paired with rubidium atoms. “Although the Rydberg pulse is global, only Cs atoms paired with Rb atoms acquire the conditional phase,” the researchers state, highlighting the precision of this method.

Two shuttling pair sets, $Q^1$ and $Q^2$, are defined to facilitate the controlled-phase gate on target caesium-caesium pairs. The resulting GRAIL instruction sequence, G_(Rb)(H)CP(Q^1;π)G_(Rb)(H)CP(Q^2;φ) ∘ G_(Rb)(H)CP(Q^1;π)$G_{Rb}(H)$, implements a controlled-phase gate on each target pair while returning the addressor atom to its initial, disentangled state. This design allows for physical CZ gates with φ set to π, demonstrating the versatility of the GRAIL instruction set.

The system’s design also allows for the creation of a native physical gate set consisting of Hadamard, T, and CZ gates, predicting fidelities exceeding 99. 5% for all compiled physical gates. This is achieved by combining global reset and measurement, which act on all atoms in a specified species, with the selective application of Rydberg interactions and atom shuttling.

Crosstalk Suppression Achieves Error Rates Below 10^(-4)

Simulations demonstrate that crosstalk errors in the implemented quantum system remain below 0.1% when the Rydberg Rabi frequency reaches 12 MHz, a figure that scales inversely with driving strength and offers a pathway to further suppression. The hardware-inferred circuit-level noise model used in these simulations incorporates both unitary and dissipative dynamics, providing a realistic assessment of gate performance.

43% Error Threshold for ZXXZ Surface Code Memory

Simulations reveal a quantum memory built on globally driven atom arrays can maintain fault tolerance even with a 1. 43% physical error rate. The system’s ability to suppress crosstalk errors to the ${10}^{–4}$ level is critical to this stability, allowing for reliable operation despite inherent noise. This approach differs from many existing quantum computing designs by replacing local gate addressing with atom-mediated selectivity, removing associated calibration requirements.

Magic State Cultivation Yields Logical Error Rate Below 10^(-9)

A logical error rate below ${10}^{–9}$ was obtained for magic states cultivated at an experimentally accessible Rydberg Rabi frequency. The architecture underpinning this result distinguishes itself by replacing localized control of individual atoms with a globally driven approach, simplifying the demands on calibration and scaling. Simulations indicate the system remains fault-tolerant even when accounting for crosstalk, exhibiting an error-correction threshold of 1.43%.

The cultivation of magic states, essential for universal quantum computation, was benchmarked using a five-fold transversal MSC protocol. This protocol requires the preparation of a GHZ ancilla and a controlled-H_(XY) gate. A parallelized scheme was developed for GHZ ancilla preparation to minimize the overall pulse depth of the operation. The architecture’s reliance on globally driven atom arrays offers a potential solution to the challenges of scaling up quantum computers.

By decoupling programmable qubit addressability from local quantum control, the system reduces the complexity associated with calibrating and controlling individual atoms. This approach could lead to building larger, more reliable quantum computers capable of tackling problems beyond the reach of classical machines.

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