Grant: Research Tools and Instruments - Category 1 (<$150,000)

Quantum computers, which perform their operations on coherent superpositions of quantum states, or ""qubits"", rather than on the more normal ""1"" and ""0"" bits of our now ubiquitous digital computers, hold out the promise of solving certain classes of problems much faster than any conceivable digital computer. This promise has resulted in an enormous worldwide interest in developing a quantum computer technology. Much of this interest is focused on semiconductor-based approaches, and within that subset much effort is going into schemes for silicon-based quantum computation, given the highly developed state of silicon materials science and device processing technology. We have discovered new optical methods of reading out and controlling the electron and nuclear spins of donor impurities in silicon. Donor impurities, of which phosphorus is the most well known in silicon, are atoms which replace a silicon atom in the crystal, and at low temperatures have an extra electron weakly bound to the positive donor ion. All of the common donors in silicon also have nuclei with nonzero nuclear spin. It is these donor electron and nuclear spins which are leading qubit candidates for silicon-based quantum computing. We have used our new optical methods to measure record-breaking coherence times for the phosphorus nuclear spin - the time during which the quantum information remains uncorrupted. The requested equipment will allow us to manipulate the donor electron spins as well as the nuclear spins, enabling us to measure and control all the parameters of the system. This will also enable the creation and measurement of entangled states, in which the electron and nuclear spins are coupled in ways that can only be understood quantum mechanically. These entangled states are at the heart of quantum computation.