Hierarchically Coupled Quantum LDPC Codes for Modular Quantum Computing

Hessam Mahdavifar, Northeastern University (Principal Investigator)

Ivana Dimitrova, Northeastern University (Co-Investigator)

Future large-scale quantum computers will likely require modular architectures consisting of many interconnected quantum processors rather than a single monolithic device. While modularity offers a practical path toward scalability, it also introduces major challenges for quantum error correction because communication between modules is slower, noisier, and less reliable than operations performed locally within each processor. Addressing these challenges is essential for realizing fault-tolerant quantum computing capable of solving scientifically and technologically important problems.

This project studies quantum error-correction methods and decoding strategies for modular quantum computing systems, with a particular focus on neutral-atom quantum processors connected through photonic interconnects. Neutral-atom quantum processors are especially promising for near-term implementation of modular error-correction schemes: they offer a large number of qubits in each module and provide natural access to photons through laser excitation and emission. The research will investigate how to efficiently coordinate local and distributed error correction under realistic hardware and communication constraints.

The project combines advances in quantum coding theory, decoding algorithms, and experimentally informed models of photonic interconnects. The research will progress along three integrated directions:

1. Development and analysis of scalable quantum low-density parity-check (QLDPC) codes suitable for modular quantum architectures.
2. Modeling and analysis of achievable remote entanglement fidelities, communication rates, and operational constraints for next-generation photonic interconnects, featuring a continuous stream of fresh atoms and time-multiplexing for increased communication rates and time-bin atom-photon entanglement for robust operation.
3. Design of efficient and highly parallelized decoding algorithms capable of processing noisy quantum syndrome information under realistic timing and communication limitations.

The anticipated outcomes include new theoretical foundations and practical design principles for scalable fault-tolerant modular quantum computing. More broadly, the project will advance the development of next-generation quantum computing technologies relevant to scientific computing, information processing, and large-scale quantum systems.