The Workshop on Quantum Computing and Quantum Information was held on June 3, 2019 at Tokyo, Japan, in conjunction with the 18 th International Conference on Unconventional Computation and Natural Computation (UCNC 2019).The Workshop was initiated by UCNC program committee members Shinnosuke Seki and Jarkko Kari, who suggested to the organizers that such a workshop could be beneficial.In the end of 2018, the program committee was assembled, and the call for papers was published subsequently.The topic area of the workshop was defined very broadly, and from the very beginning it was clear that the workshop should distinguish from the main event so that presentations including non-finished ideas should be also welcomed, and this was explicitly mentioned in the letter calling for papers.All submitted papers were peer-reviewed and the program committee accepted four contributions to be presented in the workshop.Unfortunately one manuscript was withdrawn by the authors, due to an unsuspected personal restriction for presenting the manuscript in the workshop.In addition to the contributing papers, the workshop included one plenary talk.Mika Hirvensalo gave a lecture on the role of interference in computing.
We study two families of error-correcting codes defined in terms of very sparse matrices. "MN" (MacKay-Neal (1995)) codes are recently invented, and "Gallager codes" were first investigated in 1962, but appear to have been largely forgotten, in spite of their excellent properties. The decoding of both codes can be tackled with a practical sum-product algorithm. We prove that these codes are "very good", in that sequences of codes exist which, when optimally decoded, achieve information rates up to the Shannon limit. This result holds not only for the binary-symmetric channel but also for any channel with symmetric stationary ergodic noise. We give experimental results for binary-symmetric channels and Gaussian channels demonstrating that practical performance substantially better than that of standard convolutional and concatenated codes can be achieved; indeed, the performance of Gallager codes is almost as close to the Shannon limit as that of turbo codes.
This paper presents a new class of easily invertible circulant matrices, defined by exploiting the isomorphism from the ring Mnof n times n circulant matrices over GF(p) to the ring Rn= GF(p)[x]/(xn- 1) of the polynomials modulo (xn- 1). Such class contains matrices free of 4-length cycles that, if sparse, can be included in the parity check matrix of QC-LDPC codes. Bounds for the weight of their inverses are also determined, that are useful for designing sparse generator matrices for these error correcting codes.