Absence of a dissipative quantum phase transition in Josephson junctions: Theory

• URL: http://arxiv.org/abs/2312.14754v4
• Date: Wed, 30 Oct 2024 16:46:30 GMT
• Title: Absence of a dissipative quantum phase transition in Josephson junctions: Theory
• Authors: Carles Altimiras, Daniel Esteve, Çağlar Girit, Hélène le Sueur, Philippe Joyez,
• Abstract summary: We investigate the resistively shunted Josephson junction (RSJ) at equilibrium. We find that shunting a junction makes it more superconducting. We reveal that the UV cutoff of the resistor plays an unforeseen key role in these systems.
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• Abstract: We investigate the resistively shunted Josephson junction (RSJ) at equilibrium, using exact path integral techniques. Our writing of the effective action makes it clear that the superconducting - insulating quantum phase transition long believed to occur in the RSJ, cannot exist. This can be traced to translational invariances in the Caldeira-Leggett Hamiltonian making the junction's reduced ground state highly degenerate and actually lacking the symmetry that the transition is supposed to break. For all parameters, we find that shunting a junction makes it more superconducting. We reveal that the UV cutoff of the resistor plays an unforeseen key role in these systems, and show that the erroneous prediction of an insulating state resulted in part from ill-assuming it would not. Our results fully support and confirm the experimental invalidation of this quantum phase transition by Murani et al. in 2020.

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