  Recent progresses in Josephson-junction-based superconducting circuits have
propelled quantum information processing forward. However, the lack of a
metastable state in most superconducting artificial atoms hinders the
development of photonic quantum memory in this platform. Here, we use a single
superconducting qubit-resonator system to realize a desired $\Lambda$-type
artificial atom, and to demonstrate slow light with a group velocity of 3.6
km/s and the microwave storage with a memory time extending to several hundred
nanoseconds via electromagnetically induced transparency. Our results highlight
the potential of achieving microwave quantum memory, promising substantial
advancements in quantum information processing within superconducting circuits.
