Probing the influence of many-body fluctuations on Cooper pair tunneling using circuit QED

Because of the value of the hyperfine constant (~ 1/137) observing many body effects in light-matter interaction is challenging. Reaching this regime is now possible using the tools of circuit Quantum ElectroDynamics (cQED) [1,2].
In this work we investigate the interactions between the plasma modes propagating in arrays of more than 4000 SQUIDs (which simulate the light) and a small Josephson junction (the matter). The first effect of these modes is to broaden the energy level of the Josephson junction [1,2]. More interestingly they can also induce strong phase fluctuations across the junction, which directly affects the Cooper pair tunneling. We will present our on-going experimental efforts aimed at observing this purely quantum many-body effect.

[1] P. Forn-Díaz, et al. “Ultrastrong coupling of a single artificial atom to an electromagnetic continuum in the nonperturbative regime,” Nature Physics, 13(1), 39–43 (2016).
[2] J. Puertas Martínez, S.Léger, et al. “A tunable Josephson platform to explore many-body quantum optics in circuit-QED,” arXiv:1802.00633.