Bringing Classical LDPC Code Design Theory to Quantum Computers

Insider Brief

• A new quantum LDPC code adapts classical design principles to pursue high encoding rates, strong error protection and predictable decoding performance.
• The code protects 4,612 logical qubits with 9,216 physical qubits and shows strong evidence of a minimum distance near 48.
• Independent research teams have adapted the approach, known as Kasai codes, for neutral-atom hardware and broader error-correction frameworks.
• Image: Institute of Science Tokyo

PRESS RELEASE — Quantum error correction must detect and correct errors without directly reading the quantum information. Classical low-density parity check (LDPC) codes have a well-established design theory: by choosing how many checks connect to each bit, retaining appropriate randomness, and avoiding short loops, designers can pursue both a large minimum distance and a threshold phenomenon in which the decoding failure rate drops sharply below a predicted noise level. Quantum LDPC codes must additionally make two types of error checks orthogonal so that they do not interfere. Applying this quantum mechanical constraint throughout the full design can create short loops and weak structures, making it difficult to retain both classical advantages.