Superconducting transmission lines with pulse-controlled dispersion

To control phase velocity in superconducting transmission lines using short electrical pulses, a few approaches are being developed. A new design is developed for left-to-right (L2R) and right-to-left (R2L) tunable transmission lines based on a CPW with embedded paired resonators containing dc-SQUIDs. Experimental layouts are designed according to rules of 2-µm Nb-Al/AlO
x
-Nb technology for J
c
≈ 0.1 kA/cm
²
and compared numerically with a scheme-model containing 40 cells at frequencies up to 20 GHz. Characteristic impedance of new dispersive transmission lines is increased above 30 Ohm; a thin-film attenuator is integrated for suppression of standing waves. A stop-band is found for R2L line demonstrating slower phase velocity; this transmission gap is due to effect of shorter wavelength (up to 100 times) reaching electrical length of the paired resonators cell (70 µm). In case of L2R line with faster phase velocity, the transmission band can be almost flat, if simultaneous tuning of frequency for all paired resonators is provided. No negative phase velocity is found in the simulations; however, the increment of differential phase velocity is positive for R2L near edge of the stop-band and negative near the resonance for L2R case.