Quantum phase slips in Josephson junction rings

Article

关键词: DYNAMICS;    FLUCTUATIONS;    TRANSITIONS;   

DOI  :  10.1103/PhysRevB.87.174513

来源: SCIE

【 摘 要 】

We study quantum phase-slip (QPS) processes in a superconducting ring containing N Josephson junctions and threaded by an external static magnetic flux Phi(B). In such a system, a QPS consists of a quantum tunneling event connecting two distinct classical states of the phases with different persistent currents [Matveev et al., Phys. Rev. Lett. 89, 096802 (2002)]. When the Josephson coupling energy E-J of the junctions is larger than the charging energy E-C = e(2)/2C, where C is the junction capacitance, the quantum amplitude for the QPS process is exponentially small in the ratio E-J/E-C. At given magnetic flux, each QPS can be described as the tunneling of the phase difference of a single junction of almost 2 pi, accompanied by a small harmonic displacement of the phase difference of the other N - 1 junctions. As a consequence, the total QPS amplitude nu(ing) is a global property of the ring. Here, we study the dependence of nu(ring) on the ring size N, taking into account the effect of a finite capacitance C-0 to ground, which leads to the appearance of low-frequency dispersive modes. Josephson and charging effects compete and lead to a nonmonotonic dependence of the ring's critical current on N. For N -> infinity, the system converges either towards a superconducting or an insulating state, depending on the ratio between the charging energy E-0 = e(2)/2C(0) and the Josephson coupling energy E-J.

【 授权许可】

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