  We report the experimental realization of a 3D capacitively-shunt
superconducting flux qubit with long coherence times. At the optimal flux bias
point, the qubit demonstrates energy relaxation times in the 60-90 $\mu$s
range, and Hahn-echo coherence time of about 80 $\mu$s which can be further
improved by dynamical decoupling. Qubit energy relaxation can be attributed to
quasiparticle tunneling, while qubit dephasing is caused by flux noise away
from the optimal point. Our results show that 3D c-shunt flux qubits
demonstrate improved performance over other types of flux qubits which is
advantageous for applications such as quantum magnetometry and spin sensing.
