Strategies for single spin placement and measurement in a silicon substrate

Full text: The measurement of an individual electron or nuclear spin in a solid state host material is an extraordinary challenge, yet may one day be of technological importance because spins are particularly well suited to function as qubits in quantum computers. We propose a method for measuring single spins in solid state hosts by probing two electron systems with a single electron transistor (SET). Restrictions imposed by the Pauli Principle on allowed two electron states mean that the spin state of such systems has a profound impact on the orbital state (positions) of the electrons, a parameter which SET's can measure with high precision. We outline a device architecture that can be fabricated with current technology in which a Te double electron donor is incorporated into a Si crystal below an SET located on the Si surface. We show how both electron and nuclear spin can be measured using this device. We discuss the limitations on the measurement imposed by spin scattering in the device and by the inevitable fluctuations emanating from the SET during the measurement process. A quantum computer based upon embedded spins will most likely require placement of impurities into arrays in a solid state substrate. While this task is beyond the capabilities of current technology, we are undertaking research to make small P donor arrays on a Si surface using an ultra-high-vacuum scanning tunneling microscope (STM). The STM punches atom-size holes in a monolayer of H on a Si surface, and the surface is subsequently exposed to PH3 gas. The UHV-STM is located adjacent to a Si MBE system, so that after the P atoms bond to the Si surface, they can be embedded into Si. We believe that the SET approach to single spin measurement, combined with a technology for fabricating small donor arrays, will lead to demonstrations of simple quantum logical operations in a nanostructured solid state system