Atomic defects in silicon compared with standard two-level defects

Atomic two-level systems (TLSs) in materials affect the performance of superconducting quantum devices and new fundamental studies are needed to better understand them. It was found^1,2 that the TLS bath, initially saturated by the microwave field excitations, can undergo adiabatic transitions when an additional sweeping fields is applied. Although more TLSs would remain in the ground state, the overall rate of TLSs absorbing the microwave field, increases as the sweep rate is increased due to the increase in TLS crossings in the standard distribution. It leads to a universal plataeu in non-equilibrium loss equal to the intrinsic linear dielectric loss at the low power limit. Here, we extend the measurements by using a new dielectric which is important in light of qubit substrates and semiconductor qubit devices: amorphous silicon. Quite surprisingly, the loss tangent reveals a second increases in loss with increasing bias rate. The data will be compared to previous data which fit the standard TLS model. We plan to verify the phenomenon with further studies.
¹A. L. Burin et al., Phys. Rev. Lett. 110, 157002 (2013) ²M. S. Khalil et al., Phys. Rev. B 90, 100201(R) (2014)