Broadband Two-Level System Defects Inversion Measured Through Dressed Resonator Frequency and Dielectric Loss

Two-level system (TLS) defects are known to cause performance limiting decoherence in qubits and noise in photon detectors. We have achieved a broadband TLS inversion in the GHz regime, as monitored by a resonator. The TLS inversion is caused and controlled by application of a strong pump field and a swept electric field bias. The resonator responds to the TLS inversion through changes in its resonance frequency and internal loss. For the lowest bias rates, inverted TLSs are confined in a narrow band near the pump frequency due to relaxation processes. In this regime the frequency and internal loss tangent are nearly unchanged. With increasing bias rates, a large fraction of TLSs are inverted and distributed in energy below the resonance frequency. This causes large change of resonance frequency and loss up to some maximum value. For even larger bias rates, the probability of TLS inversion is lower when interacting with the pump field due a larger probability of Landau-Zener tunneling. As a result the shifts in resonance frequency and loss lower from their respective maximum values. Numerical simulations of permittivity change agree with experimental results, and give strong evidence for broadband TLS inversion.