Glossary / Quantum computing
Quantum LDPC code
A family of error-correcting codes that protect many logical qubits with few physical ones; each check looks at only a handful of qubits.
The widely used surface code needs only neighbouring qubits to talk to each other, which makes it easy to build, but it costs hundreds to a thousand physical qubits per logical qubit. Low-density parity-check (LDPC) codes keep each check small while also linking distant qubits, which raises efficiency sharply.
In 2024 IBM described a code that protects 12 logical qubits with 288 physical qubits, about a tenth of what a surface code would need for similar performance[1]. The price is wiring between distant qubits and more complicated decoding.
Related terms
- Quantum error correctionSpreading the information of fragile qubits across many of them, so that errors can be detected and fixed.
- Logical qubitA single, robust qubit made by bundling many physical qubits together and running error correction on them.
- DecodingThe calculation that takes the measurements from error correction and works out which qubits suffered which errors.