Fabrication and Characterization of a Dimer Josephson Junction Parametric Amplifier
L.R. van Everdingen (TU Delft - Applied Sciences)
G Steele – Mentor (TU Delft - QN/Steele Lab)
C.A. Potts – Graduation committee member (TU Delft - QN/Steele Lab)
Christian Kraglund Andersen – Graduation committee member (TU Delft - Andersen Lab)
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Abstract
Superconducting qubits require a low-noise, high-gain parametric amplifier to overcome the added noise during their readout. Josephson junction arrays are suitable candidates, as they have quantum-limited added noise, large saturation power and a tunable resonance frequency. Dimer Josephson Junction Amplifier Arrays (DJJAAs) have a mode structure, which is engineered in such a way that it exploits the wave mixing processes in JPAs when amplifying incoming signals. The resonant modes in this device form pairs, referred to as dimers. The behaviour of two resonant modes in a DJJAA when a drive tone is applied at an intermediate frequency, is analyzed. A maximum gainGmax = 43.6 dB and saturation power P1dB = 105.9 dBm is measured. It is demonstrated that the mode resonance frequency shifts if the mode photon population changes. If the drive power was increased above a threshold, self-oscillations were observed in this device. A fabrication process for DJJAAs using overlap Josephson junctions was carried out iteratively. Several issues in the fabrication process were resolved. In the fabricated DJJAAs it was possible to identify and drive resonant modes for gain G > 20 dB. The resonant modes in a fabricated device did not form dimers due to offset in the Josephson inductance from its Josephson junctions compared to the design. Future efforts can improve the quality of fabricated overlap Josephson junctions and on studying nonlinear effects that were observed in the device.