Quantum error correction beyond qubits

Quantum computation and communication rely on the ability to manipulate quantum states robustly and with high fidelity. To protect fragile quantum-superposition states from corruption through so-called decoherence noise, some form of error correction is needed. Therefore, the discovery of quantum error correction1,2 (QEC) was a key step to turn the field of quantum information from an academic curiosity into a developing technology. Here, we present an experimental implementation of a QEC code for quantum information encoded in continuous variables, based on entanglement among nine optical beams3. This nine-wave-packet adaptation of Shor’s original nine-qubit scheme1 enables, at least in principle, full quantum error correction against an arbitrary single-beam error. Quantum error correction protocols eliminate uncontrolled errors that affect fragile quantum-superposition states by encoding these quantum states into a larger, multi-partite entangled system. Errors occurring on a limited number of parties will leave the entanglement intact and so the original state may be retrieved by error syndrome recognition followed by recovery operations. Shor1 proposed a concatenated quantum code to protect against arbitrary single-qubit errors, by encoding an arbitrary single-qubit state |ψ〉=α|0〉+β|1〉 into nine physical qubits