This project aims at exploring the coherence of Josephson crystals (JC) and to apply this coherence for frequency-to-current conversion. A Josephson crystal can be realized by a Josephson junction chain, formed by repeating a single junction or SQUID in space to form a one-dimensional ladder structure. Such a crystal can show a macroscopic coherent behavior due to the coherent superposition of quantum phase-slips (CQPS), ie the winding of 2 of the superconducting phase-difference occurring on single junctions. This project aims to perform a major breakthrough by addressing the coherence of circuits containing a large number of Josephson junctions. In particular this proposal aims, by novel experiments on Josephson junction chains, to understand the crucial questions of external charge dynamics and dissipation that originates from the many-body effects present in these chains. In order to fight against internal dissipation, I propose novel designs of Josephson junction chains with a disordered or fractal pattern. In addition, I propose to do a first systematic study on the external charge dynamics occurring in Josephson junction chains, in particular noise correlations. Finally, I aim to use CQPS in a Josephson crystal to realize a frequency-to-current converter. This coherent JC should, under microwave irradiation of frequency f, exhibit exact current quantization I=2nef in multiples n of the electron charge e.