We solve Schr\"odinger equation describing a tunneling macrospin coupled to a torsional oscillator. Energy spectrum is studied for various quantum regimes. Magnetic susceptibility and noise spectrum are computed. We show that entanglement of the spin with mechanical modes of a subnanometer oscillator results in the decoherence of spin tunneling. For larger oscillators the presence of a tunneling spin can be detected through splitting of the mechanical mode at the resonance. Our results apply to experiments with magnetic molecules coupled to nanoresonators.
Garanin, D. A., & Chudnovsky, E. M. (2011). Quantum entanglement of a tunneling spin with mechanical modes of a torsional resonator. Physical Review X, 1(1), 1-7. DOI: 10.1103/PhysRevX.1.011005