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The simplest Josephson junction qubit consists of a small superconducting island called ‘box’ with n excess Cooper pair charges relative to some neutral reference state.
The island is connected to a superconducting reservoir (≒ a pool, a basin of attraction) by a tunnel junction with capacitance Cj and Josephson coupling energy Wj .
A control gate voltage Vg is applied to the system through a gate capacitor Cg . Suitable values of the junction capacitance are in the range of femtofarad, the junction capacitance can be fabricated routinely by technologies at present ( about 2003 ).
