Three-body correlations in nonlinear response of correlated quantum liquid

Understanding the properties of correlated quantum liquids is a fundamental issue of condensed matter physics. Even in such a correlated case, fascinatingly, we can tell that the equilibrium fluctuations of the system govern its linear response to an external field, relying on the fluctuation dissipation relations based on the two-body correlations. Going beyond, up to the three-body correlations, is of importance for van der Waals force [1], the three-body force in nuclei [2], the Efimov state [3, 4], the ring exchange interaction in solid 3He [5, 6], and frustrated spin systems [7]. In our work, we have used a quantum dot in the Kondo regime, which is a controllable realization of such a correlated quantum liquid [8–11]. Thanks to the quality of our sample, where the Kondo effect in the unitary limit was achieved, we could quantitatively measure the three-body correlations and their role in the non-equilibrium regime, in perfect agreement with recent results of the Fermi liquid theory [12– 15]. In particular, we have demonstrated its importance when time-reversal symmetry is broken, solving a long-standing puzzle of the Kondo systems under the magnetic field [13]. The demonstrated method to relate three-body correlation and non-equilibrium transport opens up a way for further investigation of the dynamics of quantum many-body systems.