Detection of new auto-ionizing states of $^{28}$Si using resonant ionization

We are developing a scalable, solid state, quantum computer based on the Kane proposal of using $^{31}$P$^{+}$ donor ions in Si as qubits. This involves the placement of P$^{+}$ into a Si substrate with nm precision. We plan to accomplish this by laser cooling and trapping single, ablated, radioactive, $^{31}$Si atoms in a magneto-optical trap (MOT) prior to implanting them into a Si substrate. $^{31}$Si subsequently beta decays into $^{31}$P$^{+}$, forming the qubit. To gain experience before handling short lived, low abundance radioactive materials the techniques to make these measurements are being developed on $^{28}$Si. In this talk we will report on measurements of $^{28}$Si resonance ionization spectroscopy near the first ionization limit, including newly discovered auto-ionizing states. These states were detected by scanning a pulsed dye laser across a beam of excited atoms. Using this method we generated a saturation curve and calculated the photoionization cross section for the lowest lying state above the ionization limit. Additionally we will report on initial studies of laser ablation of a solid silicon sample. Research supported by the W. M. Keck Foundation and the National Science Foundation. {\dag}Fellowship support provided by the U.S. Military Academy, West Point, NY.