High-threshold and low-overhead fault-tolerant quantum memory.

Area of Science:

• Quantum Information Science
• Quantum Computing
• Error Correction Codes

Background:

• Physical errors in qubits limit the scale of current quantum computers.
• Quantum error correction (QEC) encodes logical qubits using multiple physical qubits to suppress errors.
• Practical QEC requires physical error rates below a specific threshold determined by the chosen code and decoding methods.

Purpose of the Study:

• To present a novel, end-to-end quantum error correction protocol.
• To implement fault-tolerant quantum memory using low-density parity-check (LDPC) codes.
• To demonstrate a significant reduction in qubit overhead compared to existing methods.

Main Methods:

• Utilized a family of low-density parity-check codes for quantum error correction.
• Developed a syndrome measurement circuit with depth-8 and specific qubit connectivity requirements.
• Analyzed the protocol's performance under a standard circuit-based noise model.

Main Results:

• Achieved a competitive error threshold of 0.7%, comparable to the surface code.
• Demonstrated the preservation of 12 logical qubits for nearly 1 million cycles using only 288 physical qubits at a 0.1% error rate.
• Showcased a substantial reduction in physical qubit requirements (nearly 10x fewer) compared to the surface code for equivalent performance.

Conclusions:

• The proposed LDPC-based QEC protocol offers a low-overhead solution for fault-tolerant quantum memory.
• This advancement makes fault-tolerant quantum memory demonstrations achievable on near-term quantum processors.
• The findings pave the way for executing large-scale quantum algorithms by mitigating physical error accumulation.