  We investigate the detection of quartets in hybrid multiterminal Josephson
junctions. Using simple models of quantum dots coupled to superconducting
leads, we find that quartets are ubiquitous and show how to rigorously extract
their contribution to the current-phase relation (CPR). We also demonstrate
that quartets are closely related to the hybridization of Andreev bound states
(ABSs) in these systems and propose a method to identify quartets directly in
ABS spectra. We illustrate our method by analyzing the spectroscopic
measurements of the ABS spectrum in a three-terminal Josephson junction
realized in an InAs/Al heterostructure. Our analysis strongly suggests the
existence of quartets in the studied hybrid system.
