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2012 — Wiebke Guichard, ERC starting grant

- Name of the Principal Investigator : Wiebke GUICHARD (PI)
- Name of the PI’s host institution : Université Joseph Fourier Grenoble 1/ Institut Néel
- Full Title : Frequency-to-current conversion with coherent Josephson crystals
- Short title : FrecuJoc
- Duration in months : 60 months

This project will explore quantum mechanical coherence in Josephson crystals and apply it for frequency-to-current conversion. A Josephson "crystal" can be realized by repeating a single Josephson junction or SQUID in space to form a one-dimensional ladder structure. This crystal can show a macroscopic coherent behaviour due to the coherent superposition of the quantum "phase-slips" (2π phase differences) occurring on each single junction. The coherent superposition gives rise to a novel, global non-linearity which turns the Josephson crystal into an effective “single junction” described by the dynamics of the global charge.

The enormous progress in the control of the microwave environment in superconducting quantum circuit experiments over the last ten years now makes it possible to study coherence in large multi-junction circuits experimentally. In particular this project aims, by novel experiments on Josephson junction chains, to understand the crucial questions of external charge dynamics and dissipation that originate from the many-body effects present in these chains. Scaling up the number of Josephson junctions in a circuit automatically implies the presence of low-frequency plasma modes, which lead to internal dissipation in the system and make these experiments very challenging. By using Josephson junction chains with a disordered or fractal pattern it should be possible to localize plasmon wave-functions that do not couple to the quantum states of the Josephson crystal and simultaneously keep the coherence intact. In addition, a first systematic study will be done of the external charge dynamics occurring in Josephson junction chains, in particular noise correlations.

A final aim of the project is to use the coherent superposition of quantum phase slips in a Josephson crystal to realize a frequency-to-current converter. If successful, this project will lead to a definition of the electrical current with an unprecedented precision.

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