Design and experimental study of superconducting left-handed transmission lines with tunable dispersion and improved impedance match

TL;DR

This paper presents a superconducting left-handed transmission line with tunable dispersion, achieved through Josephson junctions and SQUIDs, demonstrating adjustable frequency bands and improved measurement techniques.

Contribution

The study introduces a superconducting LHTL with tunable inductance via SQUIDs, detailed experimental characterization, and enhanced measurement setup to reduce standing waves and RF leaks.

Findings

Tunable rejection band between 10-11 GHz observed.

Single pass-band between 8-10 GHz at zero magnetic field.

Improved impedance transformer enhances measurement accuracy.

Abstract

We continue detailed study of microwave properties of a superconducting left-handed tunable CPW transmission line (LHTL). The line consists of a central conductor, loaded with series of Josephson junctions as fixed inductors; the line is shunted with SQUIDs as tunable inductors. The inductance of the SQUIDs is varied in the range of 0.08-0.5 nH by applying an external dc magnetic field. The circuit is designed to have left- and right-handed transmission bands separated by a variable rejection band. At zero magnetic field, we observed only one pass-band between 8 and 10 GHz within the frequency range of 8-12 GHz. The rejection band is anticipated to appear between 10 GHz and 11 GHz by design, and it has been detected in our previous work. To solve the problem of standing waves and RF leak in measurements of our experimental 20-cell LHTL, we have designed a high-ratio (5-50 Ohm) wideband (8-11 GHz) impedance transformer integrated at the chip, along with improved sample holder. The experimental data are compared with numerical simulations.