Efficient Concatenated Bosonic Code for Additive Gaussian Noise

Bosonic codes offer noise resilience for quantum information processing. Good performance often comes at a price of complex decoding schemes, limiting their practicality. Here, we propose using a Gottesman-Kitaev-Preskill (GKP) code to detect and discard error-prone qubits, concatenated with a quantum parity code to handle the residual errors. Our method employs a simple, linear-time decoder that nevertheless offers significant performance improvements over the standard decoder. Our work may have applications in a wide range of quantum computation and communication scenarios.