Impedance-matched Josephson parametric amplifier using open stubs as shunt capacitance*

Broadband Josephson parametric amplifiers (JPAs) are essential devices for frequency-multiplexed readout of integrated superconducting qubits towards large-scale quantum computers. Lumped capacitors such as parallel-plate capacitors are often used for such broadband JPAs to bring LC resonance with Josephson inductances to the GHz frequency region. Fabricating insulating layers of the parallel-plate capacitors makes fabrication process complex and causes additional dielectric losses.
In this presentation, we show that open stubs (open-circuited transmission lines connected at one end) can be used as shunt capacitances for JPA resonators. Such distributed elements are implemented by planar structures and thus have advantages over parallel-plate capacitors in terms of fabrication simplicity and dielectric loss. Using the open-stub structure, we experimentally demonstrate a broadband flux-driven JPA device based on impedance-matching technique, which operates at around 10 GHz with an instantaneous bandwidth of 300 MHz and saturation input power of -110 dBm.