Zero field splitting of heavy-hole states in quantum dots

Using inelastic cotunneling spectroscopy, we observe a 55{\mu}eV zero field splitting in the spin triplet manifold of Ge hut wire quantum dots. The degeneracy of the heavy hole triplet state is lifted since the interplay of strong spin orbit coupling and strong confinement leads to a preferred direction of the heavy-hole pseudospin. The reported effect should be observable in a broad class of strongly confined hole quantum-dot systems and needs to be considered when operating hole spin qubits.