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Journal Articles Physical Review X Year : 2022

Magnifying quantum phase fluctuations with Cooper-pair pairing


Remarkably, complex assemblies of superconducting wires, electrodes, and Josephson junctions are compactly described by a handful of collective phase degrees of freedom that behave like quantum particles in a potential. The inductive wires contribute a parabolic confinement, while the tunnel junctions add a cosinusoidal corrugation. Usually, the ground state wavefunction is localized within a single potential well -- that is, quantum phase fluctuations are small -- although entering the regime of delocalization holds promise for metrology and qubit protection. A direct route is to loosen the inductive confinement and let the ground state phase spread over multiple Josephson periods, but this requires a circuit impedance vastly exceeding the resistance quantum and constitutes an ongoing experimental challenge. Here we take a complementary approach and fabricate a generalized Josephson element that can be tuned in situ between one- and two-Cooper-pair tunneling, doubling the frequency of the corrugation and thereby magnifying the number of wells probed by the ground state. We measure a tenfold suppression of flux sensitivity of the first transition energy, implying a twofold increase in the vacuum phase fluctuations.

Dates and versions

hal-03084684 , version 1 (21-12-2020)





William C Smith, Marius Villiers, Antoine Marquet, Jose Palomo, Matthieu Delbecq, et al.. Magnifying quantum phase fluctuations with Cooper-pair pairing. Physical Review X, 2022, 12 (2), pp.021002. ⟨10.1103/PhysRevX.12.021002⟩. ⟨hal-03084684⟩
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