4e-condensation in a fully frustrated Josephson junction diamond chain

Fully frustrated one-dimensional diamond Josephson chains have been shown [B. Doucot and J. Vidal, Phys. Rev. Lett. 88, 227005 (2002)] to possess a remarkable property: The superfluid phase occurs through the condensation of pairs of Cooper pairs. By means of Monte Carlo simulations we analyze quantitatively the insulator to 4e-superfluid transition. We determine the location of the critical point and discuss the behavior of the phase-phase correlators. For comparison, we also present the case of a diamond chain at zero and 1/3 frustration where the standard 2e-condensation is observed.