Low Temperature Physics: 48, 400 (2022); https://doi.org/10.1063/10.0010205
Fizika Nizkikh Temperatur: Volume 48, Number 5 (May 2022), p. 450-463    ( to contents , go back )

Quantum rotator and Josephson junction: compact vs. extended phase and dissipative quantum phase transition

Edouard B. Sonin

Racah Institute of Physics, Hebrew University of Jerusalem, Givat Ram, Jerusalem 9190401, Israel
E-mail: sonin@cc.huji.ac.il
pos Анотація:870

Received January 24, 2022, published online March 25, 2022

Abstract

The paper reassesses the old dilemma “compact vs. extended phase” in the quantum theory of the rotator and the Josephson junction and the analogy of these two systems with a particle moving in a periodic potential. This dilemma is in fact the dilemma whether the states with the phases φ and φ+2π are distinguishable, or not. In the past it was widely accepted that in the Josephson junction these states are distinguishable like for a particle moving in a periodic potential. This paper argues that the states with the phases φ and φ+2π are indistinguishable as in a pendulum (a particular example of the quantum rotator). However, this does not lead to revision of the conclusions of the conventional theory predicting the transition from the superconducting to the insulating state in the small Josephson junction.

Key words: Josephson junction, dissipative quantum phase transition, quantum rotator.

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