  In studying open quantum systems, the environment is often approximated as a
collection of non-interacting harmonic oscillators, a configuration also known
as the star-bath model. It is also well known that the star-bath can be
transformed into a nearest-neighbor interacting chain of oscillators. The
chain-bath model has been widely used in renormalization group approaches. The
transformation can be obtained by recursion relations or orthogonal
polynomials. Based on a simple linear algebraic approach, we propose a bath
partition strategy to reduce the system-bath coupling strength. As a result,
the non-interacting star-bath is transformed into a set of weakly-coupled
multiple parallel chains. The transformed bath model allows complex problems to
be practically implemented on quantum simulators, and it can also be employed
in various numerical simulations of open quantum dynamics.
