Igor Golovchanskiy : Fluxonium ”spin” chains

The 1-dimensional spin chain with anisotropic exchange interaction, a.k.a. the Ising chain, is the elementary prototypical system for observation of the quantum phase transition and related phenomena. Being rarely observed in natural magnetic systems [1], the Ising chain can be constructed artificially based on the trapped ions platform [2] or by means of circuit quantum
electrodynamics [3]. In the later case, realization of the Ising chain via the fluxonium circuits is especially tempting: coupling neighbouring fluxoniums inductively via the shared kinetic inductance segments allows for realization of the ultra-strong coupling regime when the interaction energy between “spins” constitutes a significant part of the bare “spins” transition
frequency, while specifics of the matrix elements in fluxonium operators allows for crossvariation in both the transition frequency and the coupling strength with the magnetic field. This unique combination or properties favours exploration of the spectrum of the chain in a significant part of the parameter space. In this talk, we will discuss our recent experimental and theoretical studies of 1D fluxonium spin chains in different coupling regimes. We will observe the development of the band structure with predictable dispersion law, reveal the signature of the off-diagonal interactions, and explore the problem of the ferro Vs antiferromagnetic coupling. The talk will be completed by the discussion of plasmonic modes in fluxonium chains and their interaction with the “spin” modes, imitating the so-called plasmon-magnon polaritons.
[1] D. Bitko, T.F. Rosenbaum, and G. Aeppli, Phys. Rev. Lett. 77, 940 (1996)
[2] P. Jurcevic et al., Phys. Rev. Lett. Phys. Rev. Lett. 115, 100501 (2015)
[3] Oliver Viehmann, Jan von Delft, and Florian Marquardt, Phys. Rev. Lett. 110, 030601 (2013)