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Quantum phase slips in Josephson junction rings

Quantum phase slips in Josephson junction rings We study quantum phase-slip (QPS) processes in a superconducting ring containing N Josephson junctions and threaded by an external static magnetic flux Φ 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 , Phys. Rev. Lett. 10.1103/PhysRevLett.89.096802 89 , 096802 ( 2002 ) ). When the Josephson coupling energy E J of the junctions is larger than the charging energy E C = e 2 / 2 C , 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 π , accompanied by a small harmonic displacement of the phase difference of the other N − 1 junctions. As a consequence, the total QPS amplitude ν ring is a global property of the ring. Here, we study the dependence of ν 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 → ∞ , the system converges either towards a superconducting or an insulating state, depending on the ratio between the charging energy E 0 = e 2 / 2 C 0 and the Josephson coupling energy E J . http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review B American Physical Society (APS)

Quantum phase slips in Josephson junction rings

Rastelli, G; Pop, I. M; Hekking, F. W. J
Physical Review B , Volume 87 (17) – May 1, 2013
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Publisher
American Physical Society (APS)
Copyright
Copyright © 2013 The American Physical Society
ISSN
1550-235X
DOI
10.1103/PhysRevB.87.174513
Publisher site
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Abstract

We study quantum phase-slip (QPS) processes in a superconducting ring containing N Josephson junctions and threaded by an external static magnetic flux Φ 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 , Phys. Rev. Lett. 10.1103/PhysRevLett.89.096802 89 , 096802 ( 2002 ) ). When the Josephson coupling energy E J of the junctions is larger than the charging energy E C = e 2 / 2 C , 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 π , accompanied by a small harmonic displacement of the phase difference of the other N − 1 junctions. As a consequence, the total QPS amplitude ν ring is a global property of the ring. Here, we study the dependence of ν 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 → ∞ , the system converges either towards a superconducting or an insulating state, depending on the ratio between the charging energy E 0 = e 2 / 2 C 0 and the Josephson coupling energy E J .

Journal

Physical Review B – American Physical Society (APS)

Published: May 1, 2013

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