Superconducting qubits are artificial atoms assembled from electrical circuit elements. When cooled to cryogenic temperatures, these circuits exhibit quantized energy levels. Transitions between levels are induced by applying pulsed microwave electromagnetic radiation to the circuit, revealing quantum coherent phenomena analogous to (and in certain cases beyond) those observed with coherent atomic systems.

This talk begins with an overview of quantum information science and superconducting artificial atoms, including several demonstrations of quantum coherence using these circuits: Landau-Zener-Stückelberg oscillations [1], microwave-induced qubit cooling to temperatures less than 3 mK (colder than the refrigerator) [2], and a new broadband spectroscopy technique called amplitude spectroscopy [3]. We then discuss in detail a highly coherent aluminum qubit (T1=12 us, T2Echo=23 us, fidelity = 99.75%) with which we demonstrated noise spectroscopy using NMR-inspired control sequences comprising 100’s of pulses [4].

These experiments exhibit a remarkable agreement with theory, and are extensible to other solid-state qubit modalities. In addition to fundamental studies of quantum coherence in solid-state systems, we anticipate these devices and techniques will advance qubit control and state-preparation methods for quantum information science and technology applications.

[1] W.D. Oliver, et al., Science 310, 1653 (2005)
[2] S.O. Valenzuela, et al., Science (2006)
[3] D.M. Berns et al., Nature 455, 51 (2008)
[4] J. Bylander, et al., Nature Physics 7, 565 (2011)