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DATE2024.01.16 #Press Releases

New protocol for quantum computation keeps error rates low without losing efficiency

Researchers devise new quantum-computing protocol that keeps error rates low without decreasing the efficiency of memory space usage or computational time

January 16, 2024

Researchers Hayata Yamasaki and Masato Koashi of the University of Tokyo have developed a new protocol for quantum computation that makes it possible to keep error rates low without significantly damaging the efficiency of memory space usage and computational time. The duo combined multiple smaller units of error-correcting code to achieve the same effect as conventional single, large-size error-correcting codes. This new protocol contributes to taking quantum computers one step closer to large-scale functionality. The findings were published in the journal Nature Physics.

“No free lunch,” a basic principle of computer science has been causing headaches to scientists worldwide. As developers try to optimize computational processes, be it quantum or classical, they often find that improving one aspect, for example, efficiency of memory space usage, deteriorates another, for example, speed. You might get the memory space efficiency for lunch, but you have to pay for it by sacrificing speed. This principle is ever present in quantum computing, where improving the efficiency of quantum memory space usage in controlling for error rates usually disproportionately increases the necessary computational time.

One of the conventional error-controlling protocols is based on quantum low-density parity-check (LDPC) codes. This method controls error rates without a rapidly increasing need for physical qubits, the basic units of quantum computation. However, the manipulations of the quantum information encoded in the quantum LDPC code can only be run sequentially, which increases the time necessary for computation. The researchers thus wanted to see if they could create code that could be manipulated in parallel, keeping the overall running time at bay. To do this, the duo used a string of small-size quantum error-correcting codes rather than a large-size quantum LDPC code.

Although the results demonstrate the viability of the new protocol, further research is needed to investigate practical architectures on which it can be implemented.

Figure: The nested structure that produces error-corrected qubits.

For more details, please read the article:   
Hayata Yamasaki, Masato Koashi. 2024. Time-Efficient Constant-Space-Overhead Fault-Tolerant Quantum Computation. Nature Physics. DOI: 10.1038/s41567-023-02325-8