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Paper 1
A Measurement-Based Form of the Out-of-Place Quantum Carry-Lookahead Adder
Agung Trisetyarso, Rodney Van Meter, Kohei M. Itoh
- Year
- 2009
- Journal
- arXiv preprint
- DOI
- arXiv:0901.3901
- arXiv
- 0901.3901
We present the design of a quantum carry-lookahead adder using measurement-based quantum computation. The quantum carry-lookahead adder (QCLA) is faster than a quantum ripple-carry adder; QCLA has logarithmic depth while ripple adders have linear depth. Our design is evaluated in terms of number of time steps and the total number of qubits used.
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Decoder Switching: Breaking the Speed-Accuracy Tradeoff in Real-Time Quantum Error Correction
Riki Toshio, Kaito Kishi, Jun Fujisaki, Hirotaka Oshima, Shintaro Sato, Keisuke Fujii
- Year
- 2025
- Journal
- arXiv preprint
- DOI
- arXiv:2510.25222
- arXiv
- 2510.25222
The realization of fault-tolerant quantum computers hinges on the construction of high-speed, high-accuracy, real-time decoding systems. The persistent challenge lies in the fundamental trade-off between speed and accuracy: efforts to improve the decoder's accuracy often lead to unacceptable increases in decoding time and hardware complexity, while attempts to accelerate decoding result in a significant degradation in logical error rate. To overcome this challenge, we propose a novel framework, decoder switching, which balances these competing demands by combining a faster, soft-output decoder ("weak decoder") with a slower, high-accuracy decoder ("strong decoder"). In usual rounds, the weak decoder processes error syndromes and simultaneously evaluates its reliability via soft information. Only when encountering a decoding window with low reliability do we switch to the strong decoder to achieve more accurate decoding. Numerical simulations suggest that this framework can achieve accuracy comparable to, or even surpassing, that of the strong decoder, while maintaining an average decoding time on par with the weak decoder. We also develop an online decoding scheme tailored to our framework, named double window decoding, and elucidate the criteria for preventing an exponential slowdown of quantum computation. These findings break the long-standing speed-accuracy trade-off, paving the way for scalable real-time decoding devices.
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