Fermionic Stoner-Dicke phase transition in Circuit Quantum Magnetostatics

TL;DR

This paper introduces a minimal, tunable fermionic system coupled to quantum magnetic flux that displays phenomena like Stoner instability and Dicke phase transition, expanding understanding of magnetic and quantum phase behaviors in circuit QED.

Contribution

It presents an analytically solvable model of fermions coupled to magnetic flux, revealing new many-body phenomena and nonlinear phases in circuit quantum electrodynamics systems.

Findings

Demonstrates Stoner orbital instability and Dicke-like phase transition in the model.

Explores nonlinear flux-matter phases with Josephson junctions.

Shows tunable nonlinearity in tight-binding systems without actual JJs.

Abstract

We present a minimal tunable many-body system of fermions coupled to quantum magnetic flux, which is analytically diagonalizable and exhibits a variety of many-body phenomena such as Stoner orbital instability and Dicke-like quantum phase transition. In contrast to standard cavity quantum electrodynamics with its electric-dipole coupling of the electric field operators with matter, here it is the quantized magnetic field of an LC-resonator which is coupled to the angular momentum of particles. Adding the Josephson junction (JJ) to the linear LC circuit allows us to explore nonlinear flux-matter phases and sector-selective photon dressing in regimes relevant to circuit QED and mesoscopic rings. Furthermore, we consider the tight-binding systems that exhibit a tunable nonlinearity representing artificial JJ, but without actual JJs included in the circuit.