  Superconducting quantum circuits based on Josephson junctions have made rapid
progress in demonstrating quantum behavior and scalability. However, the future
prospects ultimately depend upon the intrinsic coherence of Josephson
junctions, and whether superconducting qubits can be adequately isolated from
their environment. We introduce a new architecture for superconducting quantum
circuits employing a three dimensional resonator that suppresses qubit
decoherence while maintaining sufficient coupling to the control signal. With
the new architecture, we demonstrate that Josephson junction qubits are highly
coherent, with $T_2 \sim 10 \mu$s to $20 \mu$s without the use of spin echo,
and highly stable, showing no evidence for $1/f$ critical current noise. These
results suggest that the overall quality of Josephson junctions in these qubits
will allow error rates of a few $10^{-4}$, approaching the error correction
threshold.
