Fig. 3: Stabilization protocol and results.
From: Trade off-free entanglement stabilization in a superconducting qutrit-qubit system
a Energy level diagram showing the action of Ωl,r (blue), \({g}_{l,r}^{01}\) (purple), \({g}_{l,r}^{12}\) (magenta), and κ (orange). Only the first two energy levels of the resonators are shown for clarity. b Stabilization trajectory for transmons initialized in \(\left|00\right\rangle\) obtained for Ωl,r = 2π × 7.2 MHz, \({g}_{l,r}^{01}=2\pi \times 7.5\) MHz, \({g}_{l}^{12}=2\pi \times 13.1\) MHz, κ = 2π × 4.73 MHz, showing target state (here \(\left|T\right\rangle\)) fidelity of 84% fidelity stabilized for 50 μs. The dashed line corresponds to trajectories obtained using master equation simulations. The density matrix at t = 50 μs, reconstructed using quantum state tomography, shows that most of steady-state error is accounted for by decay into \(\left|00\right\rangle\). The size of the squares in the tomogram represent the magnitude, while the color represents the phase of the density matrix element. c Coherent control of the stabilized state, with simultaneous tuning of the phases of Rabi (Ωl) and parametric drives (\({g}_{l}^{01}\)), maintaining \({\phi }_{l}^{01}+{\theta }_{l}=0\). The populations are shown at a fixed time t = 2 μs as a function of drive phase and remaining drive phases fixed. The average purity and concurrence over the 2π rotation are 77%. d Two-qubit Bloch sphere representations for (normalized) projections of steady state in odd- and even-parity manifolds.
