in these systems, many derived from the fields of atomic physics and quantum optics. A few examples include: coherent superpositions of macroscopic states [@Friedman00a; @Wal00a; @Berkley03a], Rabi oscillations [@Nakamura99a; @Nakamura01; @Vion02a; @Yu02a; @Martinis02a; @Chiorescu03a; @Claudon04a; @Plourde05a; @Saito06a; @Lisenfeld07a], Landau-Zener transitions [@Izmalkov04a], Stückelberg oscillations [@Oliver05a; @Berns06a; @Sillanpaa06a; @Wilson07a; @Izmalkov08a], microwave cooling [@Valenzuela06a; @Niskanen07b; @You08a; @Grajcar08a], electromagnetically induced transparency [@Murali04a; @Dutton06a], geometrical phase [@Leek07a], and cavity quantum electrodynamics [@Chiorescu04a; @Wallraff04a; @Johansson06a; @Deppe08a; @Fink08a; @Fragner08a; @Hofheinz08a]. Significant progress has also been made toward their application to quantum information science [@Makhlin01a; @Mooij05], including state initialization [@Valenzuela06a], tunable [@Hime06a; @Ploeg07a; @Niskanen07a; @Kerman08a] and long-distance [@Sillanpaa07a; @Majer07a] coupling, quantum control [@Pashkin03a; @Yamamoto03a; @McDermott05a; @Plantenberg07a], quantum state [@Steffen06a; @Steffen06b] and process [@Neeley08a] tomography, and measurement [@Siddiqi04a; @Katz06a; @Lupascu07a; @Yamamoto08a; @Beltran08a; @Naaman08a]. For a recent review of superconducting qubits, see Ref. .

![image](Fig1_Oliver_final.png){width="5in"}

Here, we use a superconducting persistent-current qubit to implement an artificial atom [@Mooij99a; @Orlando99a]. The persistent-current qubit is a superconducting loop interrupted by three Josephson junctions (Fig. \[fig:1\]A). When biased with a static magnetic flux $f_{\textrm{dc}} \sim \Phi_0/2$, where $\Phi_0$ is the superconducting flux quantum, the system assumes a double-well potential profile (Fig. \[fig:1\]B). The diabatic ground state of the left (right) well corresponds to 