  The development of single-platform qubits, predominant for most of the last
few decades, has driven the progress of quantum information technologies but
also highlighted the limitations of various platforms. Some inherent issues
such as charge/spin noise in materials hinder certain platforms, while
increased decoherence upon attempts to scale-up severely impact qubit quality
and coupling on others. In addition, a universal solution for coherent
information transfer between quantum systems remains lacking. By combining one
or more qubit platforms, one could potentially create new hybrid platforms that
might alleviate significant issues that current single platform qubits suffer
from, and in some cases, even facilitate the conversion of static to flying
qubits on the same hybrid platform. While nascent, this is an area of rising
importance that could shed new light on robust and scalable qubit development
and provide new impetus for research directions. Here, we define the
requirements for hybrid systems with artificial atoms in solid state, exemplify
them with systems that have been proposed or attempted, and conclude with our
outlook for such hybrid quantum systems.
