Towards quantum control of an ultracoherent mechanical resonator with a fluxonium qubit

Beyond their applications in quantum computing, superconducting qubits are a powerful platform to probe various quantum phenomena in the context of hybrid quantum systems [1].  However, most of them are confined to the GHz frequency domain, limiting the class of systems they can interact with. Building upon the heavy fluxonium architecture introduced by [2], we have developed a superconducting qubit with an unprecedentedly low transition frequency of 1.8 MHz [3]. Notably, we have demonstrated a qubit with a coherence time exceeding 30 μs, a sideband cooling scheme to prepare the qubit in a pure state with 97.7% fidelity, and single-shot readout capability. Moreover, by detecting a weak charge modulation by repeated qubit interrogation, we demonstrate the high-sensitivity of this qubit architecture to a nearly resonant AC-charge drive, proving its potential in a hybrid circuit scenario. We will finally present our recent efforts to achieve the strong coupling regime between this qubit and an ultra-coherent softly-clamped mechanical membrane.

[1] Y. Chu et al. Nature 563, 666 (2018).

[2] H. Zhang et al. Physical Review X 11, 011010 (2021).

[3] Najera et al. arXiv:2307.14329 (2023). In review at PRX.