Figure 2. Spectroscopy and T₁ of two capacitively shunted flux qubits.

(a,b) Resonator and qubit spectra versus bias current used to induce the global magnetic field B. The qubit transition frequencies ω_q/2π have minima Δ_A/2π=4.36 GHz and Δ_B/2π=4.70 GHz at the qubit flux-insensitive points, which are intentionally offset in bias current (magnetic flux) by using different qubit-loop areas. (c) Energy-decay functions of qubits A and B measured at their respective degeneracy points using the inversion-recovery pulse sequence (inset). Solid lines are exponential fits with decay constant T₁.