Our manuscript introduces a new qubit formed by shunting a Josephson junction of twisted d-wave superconductor with a large capacitance, and studies its inherent protection against decoherence. You can view the arXiv pre-print here.

This was a collaborative work led by Valentina Brosco from ISC-CNR in Rome, with support from Valerii Vinokur of Terra Quantum, as well as our long-term local collaboration with the group of Nicola Poccia at the IFW Dresden. We build on recent experiments on twisted cuprate van-der-Waals Josephson junctions, which have a unique property where single Cooper pair tunneling disappears at 45 degrees, leading to a current phase relationship dominated by double Cooper pair tunneling. This is a single junction implementation of the “cos(2phi)” double well potential. By shunting the junction with a large capacitor, we make a new qubit that we call the ‘flowermon’, where the low energy states are delocalized in the two wells. The flowermon is thus protected from electric field noise for either charge and dissipation, while having no loops or requiring any parameter calibration.

This measurement is interesting for future quantum technology, but also a perfect example of the hybrid vision where a unique property of a quantum material can be utilized to create novel coherent quantum devices.

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