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The large number of degrees of freedom associated with a solid-state device makes it more difficult to maintain the coherence.
For now ( about 2003 ), this problem has been satisfied by either resorting to well-isolated spins or making use of the quasi-particle spectrum in superconductors.
All proposed superconducting quantum circuits are based on superconducting structures containing Josephson junctions.
A Josephson junction is a structure consisting of two superconducting electrodes by a thin dielectric tunnel barrier.
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