Logical quantum processor based on reconfigurable atom arrays (2312.03982v1)

Abstract: Suppressing errors is the central challenge for useful quantum computing, requiring quantum error correction for large-scale processing. However, the overhead in the realization of error-corrected ``logical'' qubits, where information is encoded across many physical qubits for redundancy, poses significant challenges to large-scale logical quantum computing. Here we report the realization of a programmable quantum processor based on encoded logical qubits operating with up to 280 physical qubits. Utilizing logical-level control and a zoned architecture in reconfigurable neutral atom arrays, our system combines high two-qubit gate fidelities, arbitrary connectivity, as well as fully programmable single-qubit rotations and mid-circuit readout. Operating this logical processor with various types of encodings, we demonstrate improvement of a two-qubit logic gate by scaling surface code distance from d=3 to d=7, preparation of color code qubits with break-even fidelities, fault-tolerant creation of logical GHZ states and feedforward entanglement teleportation, as well as operation of 40 color code qubits. Finally, using three-dimensional [[8,3,2]] code blocks, we realize computationally complex sampling circuits with up to 48 logical qubits entangled with hypercube connectivity with 228 logical two-qubit gates and 48 logical CCZ gates. We find that this logical encoding substantially improves algorithmic performance with error detection, outperforming physical qubit fidelities at both cross-entropy benchmarking and quantum simulations of fast scrambling. These results herald the advent of early error-corrected quantum computation and chart a path toward large-scale logical processors.

• The paper demonstrates a logical quantum processor that uses reconfigurable atom arrays to control logical qubits with high-fidelity two-qubit operations.
• The research details a zoned architecture incorporating storage, entangling, and readout areas, with improved logical CNOT gate fidelity observed at larger surface code distances.
• The paper validates fault-tolerant quantum operations through the implementation of color codes and 3D code blocks, paving the way for scalable quantum error correction.

Logical Quantum Processor Based on Reconfigurable Atom Arrays

This paper presents a significant advancement in the field of quantum computing with the demonstration of a programmable quantum processor structured to handle logical qubits using reconfigurable neutral atom arrays. Utilizing up to 280 physical qubits, the processor achieves logical-level control and a zoned architecture, harnessing high fidelity in two-qubit gate operations, arbitrary connectivity, and flexible single-qubit controls along with mid-circuit readouts. This innovative approach showcases several key components of quantum error correction (QEC) essential for large-scale quantum computing.

Quantum Computing and Error Correction

Quantum computing promises superior performance over classical computing for particular problem sets but is challenged by susceptibility to errors, which can significantly compromise computation without mitigation. QEC addresses this by encoding logical qubits across many physical qubits, making the system more resistant to errors. The principal goal is to operate quantum algorithms with such low logical error rates that complex quantum processes become viable, contingent on sufficiently low physical error rates and extensive error correction overhead.

Experimental Framework and Results

The researchers implement logical qubits using reconfigurable neutral atom arrays, structure them in a zoned layout encompassing storage, entangling, and readout zones, and perform quantum operations such as logical qubit encoding and gate operations. They exploit the integrated advantages of neutral atoms, such as long coherence times and low error rates, while innovating in spatial and operational configuration to achieve logical qubit operations.

Key achievements include:

• Logical CNOT Gate Improvement with Surface Code Distance: By evaluating surface code sizes ($d=3$ to $d=7$), the team demonstrates that logical entangling operations improve with increased code distance, showcasing enhanced logical gate fidelity with larger logical qubit systems.
• Fault-Tolerant Algorithms Utilizing Color Codes: The processor accurately implements fault-tolerant logical algorithms, preparing logical GHZ states with improved fidelity through flagged fault-tolerant preparations. This establishes fundamental blocks for practical quantum algorithm execution.
• Complex Circuit Implementation Using 3D Codes: Utilizing [[8,3,2]] code blocks, the research highlights execution of sampling circuits and non-trivial quantum algorithms rooted in non-Clifford operations. Performance metrics such as cross-entropy benchmarking (XEB) and indirect fidelity comparisons against classical limits reveal compelling advantages of logical operations over physical implementations.

Implications and Outlook

These advances mark forward progress towards operational quantum computation systems capable of executing error-corrected quantum algorithms, with potential implications for both quantum advantage scenarios and scalable QEC applications. The architecture's flexibility and zoned design are promising for scaling up quantum processors and refining error correction techniques through practical experimentation and implementation.

The implications suggest further research extending these methods to higher-dimensional codes and more robust implementation of QEC, possibly integrating continuous error correction cycles and exploring different quantum algorithm implementations. These efforts could eventually form the foundation for more complex and large-scale quantum computing systems, facilitating a transition toward practical quantum computation.

In conclusion, this paper not only substantiates critical pathways for achieving reliable quantum computing but also innovates foundational technologies in quantum processor design. The research conducted paves the way for future advancements in error-corrected quantum computation and large-scale processor architectures, presenting a substantial contribution to modern computational sciences.