Protecting entanglement between logical qubits via quantum error correction
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Abstract
Entanglement is one of the most important resources in quantum computing, cryptography and sensing. However, entanglement is also fragile, and its potential advantages are hindered by decoherence effects in experiments. Here we experimentally realize entangled logical qubits with a bosonic quantum module by encoding quantum information into spatially separated microwave modes. The entanglement is protected by repetitive quantum error correction, which improves the coherence time of the entangled logical qubits compared with their unprotected counterparts by 45%. In addition, we demonstrate the violation of the Bell inequality by the purified entangled logical qubits via independent error detection and post-selection on each logical qubit, resulting in measured Bell signals that surpass the classical bound. The protected entangled logical qubits could be applied in future explorations of quantum foundations and applications of quantum networks. Despite being essential to many applications in quantum science, entanglement can be easily disrupted by decoherence. A protocol based on repetitive quantum error correction now demonstrates enhanced coherence times of entangled logical qubits.