Unconditional Accumulation Of Nonclassicality In A Single-Atom Mechanical Oscillator

The robust experimental accumulation of nonclassicality of motion of a single trapped ion is reported. The nonclassicality stems from deterministic incoherent modulation of thermal phonon number distribution implemented by a laser excitation of nonlinear coupling between the ion's internal-electronic levels and external-motional states. It is demonstrated that the repetitive application of this nonlinear process monotonically accumulates the observable state nonclassicality. The output states converge to a phonon number distribution with high overlap with a particular Fock state and visible quantum non-Gaussian aspects including corresponding negative Wigner function. The resulting oscillator states prove deterministic transition in the hierarchy of quantum non-Gaussianity up to four phonons. This transition is very robust against experimental imperfections and produces increasing entanglement potential.