Q-CTRL has announced two technical advances demonstrating the integration of quantum error correction (QEC) primitives—without full logical encoding—to improve fidelity and scale of quantum operations on superconducting processors. These results include the implementation of a high-fidelity long-range CNOT gate and the generation of multipartite entangled GHZ states across up to 75 qubits.
In the first demonstration, Q-CTRL executed a long-range CNOT gate using a protocol based on the unitary preparation and disentanglement of GHZ states. The approach revealed errors through the final state of selected qubits and achieved over 85% fidelity across 40 lattice sites, outperforming previously reported superconducting methods.
In the second demonstration, the company generated GHZ states using a low-overhead routine that incorporated sparse error detection via up to nine flag qubits. Verified using multiple-quantum coherence (MQC) fidelity, the experiment produced a 75-qubit GHZ state with genuine multipartite entanglement. The discard rate was significantly reduced, with over 80% of shots retained in the 27-qubit state and over 21% in the 75-qubit case.
These results suggest that implementing QEC primitives at the physical level—without relying on full logical qubit architectures—can deliver immediate performance improvements with minimal resource overhead. The protocols developed are compatible with current-generation quantum processors and may contribute to early-stage quantum advantage in real-world applications.
The original announcement and technical details can be found here and here.
May 29, 2025
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