  Significant advances in coherence have made superconducting quantum circuits
a viable platform for fault-tolerant quantum computing. To further extend
capabilities, highly coherent quantum systems could act as quantum memories for
these circuits. A useful quantum memory must be rapidly addressable by qubits,
while maintaining superior coherence. We demonstrate a novel superconducting
microwave cavity architecture that is highly robust against major sources of
loss that are encountered in the engineering of circuit QED systems. The
architecture allows for near-millisecond storage of quantum states in a
resonator while strong coupling between the resonator and a transmon qubit
enables control, encoding, and readout at MHz rates. The observed coherence
times constitute an improvement of almost an order of magnitude over those of
the best available superconducting qubits. Our design is an ideal platform for
studying coherent quantum optics and marks an important step towards
hardware-efficient quantum computing with Josephson junction-based quantum
circuits.
