Superconducting materials are a natural choice for building solid-state quantum circuits, since superconductivity offers coherence. Superconductors have a region in the energy spectrum, in which only one energy level exists, the Fermi level, while all other energy levels are separated from it by the superconducting energy gap. Cooper pairs of conducting electrons condense to this energy level, which appears to be protected from low-energy excitations because of the presence of the gap. This allows to prepare, control and manipulate quantum states in superconductor-based nanocircuits for the use in various devices whose operation is based upon quantum principles.

In my presentation, I will give an overview of the field and cover several experiments in which superconducting nandevices with a charge and flux degrees of freedom were used as solid-state qubits [1-3], artificial atoms [4] and charge pumps [5].

[1] Y. Nakamura, Yu.A. Pashkin, and J.S. Tsai, Nature 398, 786 (1999).
[2] Yu.A. Pashkin et al., Nature 421, 823 (2003).
[3] T. Yamamoto et al., Nature 425, 941 (2003).
[4] O. Astafiev et al., Science 327, 840 (2010).
[5] J.P. Pekola et al., Rev. Mod. Phys. 85, 142 (2013).