Uniqueness for an inverse coefficient problem of a weakly coupled parabolic system

This paper considers the weakly coupled parabolic system $\partial_t u-\partial^2_xu +P(x)u=0$ with the homogeneous Neumann boundary condition, where $P(x)$ is a $2\times2$ symmetric real-valued function matrix. Under the assumption that the initial value $a(x)$ is a generating element (i.e., it has a nonzero inner product with every eigenfunction), we prove that the coefficient matrix $P(x)$ is uniquely determined by the boundary observation $u(0, t)$, $u(1, t)$, $0 < t < T$. The proof relies on the eigenfunction expansion of the solution to the initial-boundary value problem and an extension of the Gel'fand-Levitan theory to the parabolic system.