  N\'eel ordered antiferromagnets exhibit two-mode squeezing such that their
ground state is a nonclassical superposition of magnon Fock states. Here we
theoretically demonstrate that antiferromagnets can couple to spin qubits via
direct dispersive interaction stemming from, e.g., interfacial exchange. We
demonstrate that this kind of coupling induces a magnon number dependent level
splitting of the excited state resulting in multiple system excitation
energies. This series of level splittings manifests itself as nontrivial
excitation peaks in qubit spectroscopy thereby revealing the underlying
nonclassical magnon composition of the antiferromagnetic quantum state. By
appropriately choosing the drive or excitation energy, the magnonic state can
be controlled via the qubit, suggesting that Fock states of magnon pairs can be
generated deterministically. This enables achieving states useful for quantum
computing and quantum information science protocols.
