We report on a method for detecting weakly coupled spurious two-level system fluctuators (TLSs) in superconducting qubits. This method is more sensitive that standard spectroscopic techniques for locating TLSs with a reduced data acquisition time.
We demonstrate coherent tunable coupling between a superconducting phase qubit and a lumped element resonator. The coupling strength is mediated by a flux-biased RF SQUID operated in the non-hysteretic regime. By tuning the applied flux bias to the R
F SQUID we change the effective mutual inductance, and thus the coupling energy, between the phase qubit and resonator . We verify the modulation of coupling strength from 0 to $100 MHz$ by observing modulation in the size of the splitting in the phase qubits spectroscopy, as well as coherently by observing modulation in the vacuum Rabi oscillation frequency when on resonance. The measured spectroscopic splittings and vacuum Rabi oscillations agree well with theoretical predictions.
