Quantum model of a solid-state spin qubit: Ni cluster on a silicon   surface by the generalized spin Hamiltonian and X-ray absorption spectroscopy   investigations
  We present here the quantum model of a Ni solid-state electron spin qubit on a silicon surface with the use of a density functional scheme for calculation of the exchange integrals in the non-collinear spin configurations in the generalized spin Hamiltonian (GSH) with the anisotropic exchange couplings parameters linking the nickel ions with a silicon substrate. In this article we offer the model of the quantum solid-state N-spin qubit based on the studying of the spin structure and the spin-dynamics simulations of the 3d-metal Ni clusters on a silicon surface. The solution of the problem of the entanglement between a spin states in N-spin systems is becoming more interesting when considering clusters or molecules with a spectral gap in their density of states. For quantifying the distribution of the entanglement between the individual spin eigenvalues (modes) in the spin structure of the N-spin system we use the density of entanglement. We have studied the Rabi oscillations to evaluate the N-spin qubits system as a function of the time and the magnetic field. We have observed the stabilized Rabi oscillations and have stabilized the quantum dynamical qubit state and Rabi driving after a fixed time. The comparison of the energy pattern with the anisotropic exchange models conventionally used for the analysis of this system and, with the results of the experimental XANES spectra, shows that our complex investigations provide a good description of the pattern of the spin levels and the spin structures of the nanomagnetic Ni7 qubit. The results are discussed in the view of the general problem of the solid state spin qubits and the spin structure of the Ni cluster. 
Oleg V.Farberovich, Victoria L.Mazalova, Alexander V.Soldatov
cond-mat.mes-hall cond-mat.mtrl-sci physics.atm-clus physics.comp-ph