Figure 1

(Color online) Schematic diagram of two charge qubits coupled by a (left) large Josephson junction (JJ) with coupling energy $E_{J0}$ and capacitance $C_{J0}$. For the $i\text{th}$ charge qubit (where $i=1,2$), a superconducting island (denoted by a filled circle) is connected to two identical small JJs (each with coupling energy $E_{Ji}$ and capacitance $C_{Ji}$). Also, this island is biased by the voltage $V_i=V_{Xi}+V_g^{\left(i\right)}\left(t\right)$ via a gate capacitance $C_i$, where $V_{Xi}$ is a static (dc) gate voltage and $V_g^{\left(i\right)}\left(t\right)$ is a time-dependent (ac) microwave gate voltage. Moreover, a static (dc) magnetic flux ${\Phi }_e$ plus a microwave-field-induced magnetic flux $\Phi \left(t\right)$ (ac) are applied to the (yellow) region between the large JJ and the first charge qubit.Reuse & Permissions

Figure 2

The photon number distribution $P\left(n\right)$ with average photon number $\overline{n}=7$ of (a) coherent state $|\alpha ⟩$; (b) superposition of coherent states $\left(|\alpha ⟩+|-\alpha ⟩\right)∕N_{+}$; and (c) squeezed vacuum state $|0,\zeta ⟩$.Reuse & Permissions

Figure 3

Evolution ${\kappa }_q\left(\tau \right)$ of the reduced total supercurrent expectation and reduced supercurrent fluctuation from the initial qubit state $\left(|g,g⟩+|e,e⟩\right)∕\sqrt{2}$ in the presence of the quantum field initially in (a) coherent state $|\alpha ⟩$ with the phase $\phi =\pi ∕2$; (b) coherent state $\phi =0$; (c) superposition of coherent states $\left(|\alpha ⟩+|-\alpha ⟩\right)∕N_{+}$ with $\phi =0$; (d) squeezed vacuum state $|0,\zeta ⟩$. The irregularity of oscillations originates from the interference effect of the photon component of the above states. Note that both ${\kappa }_q\left(\tau \right)$ and the rescaled time $\tau$ are dimensionless.Reuse & Permissions