Direct observation of a threshold for coherent radiation in unshunted Josephson-junction arrays with ground planes
Branimir Vasilić, Paola Barbara, S. V. Shitov, Christopher J. Lobb · Physical review. B, Condensed matter · 2002
Previous experiments [Barbara et al., Phys. Rev. Lett. 82, 1963 (1999); Vasili\ifmmode \acute{c}\else \'{c}\fi{} et al., Appl. Phys. Lett. 78, 1137 (2001)] showed that two-dimensional, unshunted Josephson-junction arrays emit radiation coherently when a threshold number of junctions is switched to a radiating state. Here, we report low-power radiation being emitted when the number of radiating junctions is smaller than the threshold number. We show that in this regime the output power is incoherent, i.e., the array behavior is qualitatively different from the coherent regime.