Granular Aluminum: a superconducting material with amenable nonlinearity for quantum circuits

The electrodynamics of granular Aluminum (grAl) in the microwave domain can be modeled using an effective Josephson junction array, which exhibits intrinsically high kinetic inductance, amenable nonlinearity [1,2] and relatively low dissipation [3]. These atributes recommend grAl for various applications in quantum technology, including kinetic inductance detectors, parametric amplifiers and quantum bits. One illustration of grAl's utility in quantum circuit design is the remarkable resilience of grAl fluxonium qubits [4] to photons populating the readout resonator. This resilience allows single shot QND measurements [5] and quantum state preparation via active feedback with fidelities exceeding 90% even without using a parametric amplifier [6]. An outstanding challenge is the mitigation of non-equilibrium quasiparticles, and in particular the abatement of quasiparticle bursts due to ionizing radiation interactions with the device substrate [7].

Refrences: [1] Maleeva et al. Nature Comm. 9, 3889 (2018), [2] Winkel et al. Phys. Rev. X 10, 031032 (2020), [3] Grunhaupt et al. Phys. Rev. Lett. 121, 117001 (2018), [4] Grunhaupt, Spiecker et al. Nature Materials 18, 816-819 (2019), [5] Takmakov, Winkel, et al. Phys. Rev. App. 15, 064029 (2021), [6] Gusenkova, Spiecker, et al. Phys. Rev. App. 15, 064030 (2021), [7] Cardani, Valenti et al. Nat. Commun. 12, 2733 (2021).