  Superconducting microwave cavities with ultra-high Q-factors are
revolutionizing the field of quantum computing, offering long coherence times
exceeding 1 ms, which is critical for realizing scalable multi-qubit quantum
systems with low error rates. In this work, we provide an in-depth analysis of
recent advances in ultra-high Q-factor cavities, integration of Josephson
junction-based qubits, and bosonic-encoded qubits in 3D cavities. We examine
the sources of quantum state dephasing caused by damping and noise mechanisms
in cavities and qubits, highlighting the critical challenges that need to be
addressed to achieve even higher coherence times. We critically survey the
latest progress made in implementing single 3D qubits using superconducting
materials, normal metals, and multi-qubit and multi-state quantum systems. Our
work sheds light on the promising future of this research area, including novel
materials for cavities and qubits, modes with nontrivial topological
properties, error correction techniques for bosonic qubits, and new
light-matter interaction effects.
