Nondegenerate Parametric Amplifiers Based on Dispersion-Engineered Josephson-Junction Arrays
Patrick Winkel, Ivan Takmakov, Dennis Rieger, Luca Planat, Wiebke Hasch-Guichard, Lukas Grünhaupt, Nataliya Maleeva, Farshad Foroughi, Fabio Henriques, Kiril Borisov, Julian Ferrero, Alexey V. Ustinov, Wolfgang Wernsdorfer, Nicolas Roch, Ioan M. Pop
Abstract
Determining the state of a qubit on a time scale much shorter than its relaxation time is an essential requirement for quantum information processing. With the aid of a nondegenerate parametric amplifier, we demonstrate the continuous detection of quantum jumps of a transmon qubit with $90\mathrm{%}$ fidelity of state discrimination. Entirely fabricated by standard two-step optical-lithography techniques, this type of parametric amplifier consists of a dispersion-engineered Josephson-junction (JJ) array. By using long arrays, containing ${10}^{3}\phantom{\rule{0.2em}{0ex}}\mathrm{JJs}$, we can obtain amplification in multiple eigenmodes with frequencies below $10\phantom{\rule{0.2em}{0ex}}\mathrm{GHz}$, which is the typical range for qubit readout. Moreover, if a moderate flux tunability of each mode is introduced, employing superconducting-quantum-interference-device junctions, a single amplifier device could potentially cover the entire frequency band between 1 and 10 GHz.