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Paper 1

Quaternary Neural Belief Propagation Decoding of Quantum LDPC Codes with Overcomplete Check Matrices

Sisi Miao, Alexander Schnerring, Haizheng Li, Laurent Schmalen

Year

2023

Journal

arXiv preprint

DOI

arXiv:2308.08208

arXiv

2308.08208

Quantum low-density parity-check (QLDPC) codes are promising candidates for error correction in quantum computers. One of the major challenges in implementing QLDPC codes in quantum computers is the lack of a universal decoder. In this work, we first propose to decode QLDPC codes with a belief propagation (BP) decoder operating on overcomplete check matrices. Then, we extend the neural BP (NBP) decoder, which was originally studied for suboptimal binary BP decoding of QLPDC codes, to quaternary BP decoders. Numerical simulation results demonstrate that both approaches as well as their combination yield a low-latency, high-performance decoder for several short to moderate length QLDPC codes.

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Paper 2

Entanglement in XYZ model on a spin-star system: Anisotropy vs. field-induced dynamics

Jithin G. Krishnan, Harikrishnan K. J., Amit Kumar Pal

Year

2023

Journal

arXiv preprint

DOI

arXiv:2307.15949

arXiv

2307.15949

We consider a star-network of $n=n_0+n_p$ spin-$\frac{1}{2}$ particles, where interaction between $n_0$ central spins and $n_p$ peripheral spins are of the XYZ-type. In the limit $n_0/n_p\ll 1$, we show that for odd $n$, the ground state is doubly degenerate, while for even $n$, the energy gap becomes negligible when $n$ is large, inducing an \emph{effective} double degeneracy. In the same limit, we show that for vanishing $xy$-anisotropy $γ$, bipartite entanglement on the peripheral spins computed using either a partial trace-based, or a measurement-based approach exhibits a logarithmic growth with $n_p$, where the sizes of the partitions are typically $\sim n_p/2$. This feature disappears for $γ\neq 0$, which we refer to as the \emph{anisotropy effect}. Interestingly, when the system is taken out of equilibrium by the introduction of a magnetic field of constant strength on all spins, the time-averaged bipartite entanglement on the periphery at the long-time limit exhibits a logarithmic growth with $n_p$ irrespective of the value of $γ$. We further study the $n_0/n_p\gg 1$ and $n_0/n_p\rightarrow 1$ limits of the model, and show that the behaviour of bipartite peripheral entanglement is qualitatively different from that of the $n_0/n_p\ll 1$ limit.

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