Classical Computation in Quantum Nanostructures: A Long Road to an Uncertain Future

We have extended the spectroscopic abilities of the scanning tunneling microscope to include the measurement of spin-excitation spectra, making it possible to measure the g-value of single atoms. Utilizing spin-excitation spectroscopy as our primary tool, we are now capable of extracting exchange coupling energies, anisotropy energies, and information on the ground and excited state spin configurations of nanometer-scale structures. These experiments are playing an integral role in our efforts to engineer the ``energy landscape'' of a system of spins in order to achieve nanometer-scale binary logic circuits that operate using only the spin degree of freedom.\newline \newline Work done in collaboration with Cyrus Hirjibehedin, Andreas Heinrich, Christopher Lutz, Jay Gupta, and Bruce Melior.