Pairing of Cooper pairs in a Josephson junction network containing an impurity

¹  Dipartimento di Fisica, Università della Calabria and INFN, Gruppo Collegato di Cosenza, Arcavacata di Rende, I-87036, Cosenza, Italy, EU
²  Dipartimento di Fisica, Università di Perugia and INFN, Sezione di Perugia, Via A. Pascoli, I-06123, Perugia, Italy, EU

Corresponding authors: giuliano@fis.unical.it sodano@pg.infn.it

Received: 6 August 2009
Accepted: 16 September 2009

Abstract

We show how to induce pairing of Cooper pairs (and, thus, superconductivity) as a result of local embedding of a quantum impurity in a Josephson network fabricable with conventional junctions. We find that a boundary double sine-Gordon model provides an accurate description of the dc Josephson current patterns, as well as of the stable phases accessible to the network. We point out that tunneling of pairs of Cooper pairs is robust against quantum fluctuations, as a consequence of the time reversal invariance, arising when the central region of the network is pierced by a dimensionless magnetic flux . We find that, for , a stable attractive finite coupling fixed point emerges and point out its relevance for engineering a two-level quantum system with enhanced coherence.