Abstract
In superconducting qubit measurements, stray infrared photons lead to damping processes that degrade quantum coherence. In this Letter, we show that a thermal blocking filter made of multiwalled carbon nanotubes diluted in stainless steel powder can significantly improve the energy relaxation time, T1, and the pure dephasing time, Tφ, of a qubit. By using two independent measurement lines, with and without the filter, and switching between them in situ, we observe that with the filter there is an increase of more than 61% in T1 and 291% in Tφ. We characterize the filter, demonstrating that the scattering parameters remain stable down to 8 mK over a wide range of frequencies, spanning from 10 MHz to 50 GHz. We also show that the cutoff frequency of the filter is easily controlled by selecting the concentration of nanotubes.
© Moghaddam, M. V., Chang, C. W. S., Nsanzineza, I., Vadiraj, A. M., & Wilson, C. M. (2019). Carbon nanotube-based lossy transmission line filter for superconducting qubit measurements. Applied Physics Letters, 115(21). https://doi.org/10.1063/1.5116109