Measurement of quantum jumps of a fluxonium qubit using a Dimer Josephson Junction Array Amplifier operated at high power

Josephson parametric amplifiers have become an essential element in cQED dispersive readout measurement schemes, enabling single-shot qubit readout. Over the last decade there was significant progress in the increase of their saturation power [1,2,3,4], which now reaches several thousand photons per μs.
We demonstrate high saturation power in a Dimer Josephson Junction Array Amplifier [4] operating with a quantum efficiency of 60%. We use this parametric amplifier to perform dispersive readout of a fluxonium qubit with a superinductor made of granular aluminum [5]. We present quantum jump measurements acquired using up-to 100 circulating photons in the readout resonator, which allowed qubit state discrimination in tens of nanoseconds.

[1] C. Eichler and A. Wallraff, EPJ Quantum Technologies 1, 2 (2014)
[2] L. Planat et.al., PRA 11, 034014 (2019)
[3] V. V. Sivak et.al., arxiv:1909.08005
[4] P. Winkel & I. Takmakov et.al., arxiv:1909.08037
[5] L. Grünhaupt & M. Spiecker, et al. Nature Materials 18, 816–819 (2019)