Figure 2

Detecting quantum oscillations.

(a) shows a schematic circuit of a single-Cooper-pair box^36,37. Its Hamiltonian is described by H_CB = E_C(1–2n_g)/2(|2〉〈2|−|1〉〈1|)−E_J/2(|1〉〈2|+ |2〉〈1|), where E_J and E_C are the Josephson energy and the single-Cooper-pair charging energy of the box, respectively. The relative energy of the state with no excess Cooper pairs in the box |1〉 and the state with one excess Cooper pair |2〉, is controlled through the gate voltage, which is parametrized by n_g. The resonance of the states |1〉 and |2〉 can be brought from the initial state |1〉 by the applied voltage pulse for n_g = 0.5. (b), Detecting quantum dynamics in the resonance of the two charge states (n_g = 0.5) with the quantum witness . We use the realistic parameter E_J = 51.8 µeV. The positive regions are identified as the quantum areas.