  The combination of different quantum systems may allow the exploration of the
distinctive features of each system for the investigation of fundamental
phenomena as well as for quantum technologies. In this work we consider a setup
consisting of an atomic ensemble enclosed within a laser-driven optomechanical
cavity, having the moving mirror further (capacitively) coupled to a low
frequency LC circuit. This constitutes a four-partite optoelectromechanical
quantum system containing three macroscopic quantum subsystems of a different
nature, viz, the atomic ensemble, the massive mirror and the LC circuit. The
quantized cavity field plays the role of an auxiliary system that allows the
coupling of two other quantum subsystems. We show that for experimentally
achievable parameters, it is possible to generate steady state bipartite
Gaussian entanglement between pairs of macroscopic systems. In particular, we
find under which conditions it is possible to obtain a reasonable amount of
entanglement between the atomic ensemble and the LC circuit, systems that might
be suitable for constituting a quantum memory and for quantum processing,
respectively. For complementarity, we discuss the effect of the environmental
temperature on quantum entanglement.
