Fig. 2
From: Tuneable hopping and nonlinear cross-Kerr interactions in a high-coherence superconducting circuit
Tuneable linear coupling and single-photon hopping suppression. Top: Avoided crossings for a inductive, b zero and c capacitive coupling regimes. In all three cases, the frequency of qubit 2 is set around 6.6 GHz (Φ2 = 0), while we tune qubit 1 through resonance. Qubit spectroscopy is performed via readout resonator R2 in a, c, and via R1 in b. The coupling elements that participate more strongly to the qubit–qubit interaction are indicated in the insets. d Linear coupling strength \(\left| J \right|\) obtained from a series of fitted avoided crossings, at different values of calibrated coupler flux bias Φ3. e Eigenspectrum of the coupled qubit system on resonance vs Φ3, fitted with a simplified circuit theory model (the fitting parameters are listed in Table 1). The normal-mode splitting gets suppressed at the crossover between inductively and capacitively dominated coupler regimes (Φ3/Φ0 ≃ 0.3). Cross-talk effects between the different flux channels have been calibrated out experimentally.
