  Quantum broadcasting is central to quantum information processing and
characterizes the correlations within quantum states. Nonetheless, traditional
quantum broadcasting encounters inherent limitations dictated by the principles
of quantum mechanics. In a previous study, Parzygnat et al. [Phys. Rev. Lett.
132, 110203 (2024)] introduced a canonical broadcasting quantum map that goes
beyond the quantum no-broadcasting theorem through a virtual process. In this
work, we generalize the concept of virtual broadcasting to unilocal
broadcasting by incorporating a reference system and introduce protocols that
can be approximated using physical operations with minimal cost. First, we
propose a universal unilocal protocol enabling multiple parties to share the
correlations of a target bipartite state, which is encoded in the expectation
value for any observable. Second, we formalize the simulation cost of a virtual
quantum broadcasting protocol into a semidefinite programming problem. Notably,
we propose a specific protocol with optimal simulation cost for the
2-broadcasting scenario, revealing an explicit relationship between simulation
cost and the quantum system's dimension. Moreover, we establish upper and lower
bounds on the simulation cost of the virtual $n$-broadcasting protocol and
demonstrate the convergence of the lower bound to the upper bound as the
quantum system's dimension increases.
