Observation of individual two-level defects at material surfaces using circuit QED

The coherence of superconducting qubits have grown exponentially over the last decade. However, the coplanar electrodes used to shunt the JJ capacitance contain ubiquitous two-level system (TLS) defects on its surfaces. These defects are a major source of loss and decoherence in general, and the characteristics of the surface TLS are largely unknown. In an aluminum thin film on sapphire substrate we observe individual surface TLS using a DC electric-field bias in an interdigitated shunting capacitor with a submicron linewidth and line spacing. We use an electrical bridge of capacitors to apply the dc bias to manipulate the TLS energies allowing us to observe a hyperbolic dependence as well as splittings with the resonator. This technique allows us to capture the TLS average dipole moment as well as coherence time.