Сверхпроводящие леворукие линии передачи с импульсным управлением / Superconducting left-hand pulse-controlled transmission lines
The microwave metamaterials are artificial structures built as arrays of resonant cells, substituting atoms or molecules in solids. Such structures have unusual potentials. To control phase velocity in superconducting metamaterial transmission lines, short electrical pulses can be used. A few approaches are being developed using left-to-right (L2R) and right-to-left (R2L) tunable transmission lines based on a CPW with embedded paired resonators containing superconducting quantum interference devices (dc-SQUIDs). The inductance of SQUIDs is sensitive to pulsed magnetic field, thus changing dispersion in the line. The controlled dispersion can either concentrate EM energy for quantum bits or provide equal phase over a large area enhancing a synchronous excitation. Experimental lines are designed according to rules of 2-µm superconducting electronics using Nb-Al/AlOx-Nb Josephson junction technology for operational frequencies up to 20 GHz. 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 micron-size 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. The pulse control as short as 10 ns is possible for a 40-cell transmission line.
Figure 1 - Transmission S21 and phase shift in wavelength per 1 mm of physical length of the transmission line. Characteristics of both arrays R2L (left) and L2R (center) include 40 cells of paired resonators, but cells are different in length (20, 40 and 70µm) demonstrating enhanced delay with smaller size of the cells. The equivalent scheme (right) is a CPW loaded with SQUIDs and controlled with combination of constant and pulsed magnetic field according to the electrical current flow (H-current), as indicated by arrows (only series SQUIDs are shown for simplicity).
Scientific adviser - Shitov Sergey Vitalyevich, Dr.Sci.Phys.Math.