Classical-product code[1–3] 

A CSS code constructed by separately constructing the \(X\) and \(Z\) check matrices using product constructions from classical codes. A particular \([[512,174,8]]\) code performed well [2] against erasure and depolarizing noise when compared to other notable CSS codes, such as the asymptotically good quantum Tanner codes. These codes have been generalized to the intersecting subset code family [3].

For example, for \(H_i^x\), \(H_i^z\) being the \(X\) and \(Z\) check matrices of CSS codes \(C_i\) with \(i\in\{1,2,3,4\}\), the 2-fold symmetric classical product code is given by \begin{align} H_{\otimes}^x &:=\left(\begin{array}{c} H_1^x \otimes H_2^x \otimes I \otimes I \\ I \otimes I \otimes H_3^x \otimes H_4^x \end{array}\right) \tag*{(1)}\\ H_{\otimes}^z &:=\left(\begin{array}{c} H_1^z \otimes I \otimes H_3^z \otimes I \\ I \otimes H_2^z \otimes I \otimes H_4^z \end{array}\right)~. \tag*{(2)}\end{align}