Coherent Manipulation of Semiconductor Quantum Bits with Terahertz Radiation Mark Sherwin Department of Physics University of California Santa Barbara Quantum bits (qubits) are fundamental building blocks for quantum information processors like quantum omputers. A qubit is a pair of well-characterized quantum states which can in principle be manipulated quickly compared to the time for decoherence by coupling to the environment. There are obvious advantages to implementing quantum information processors in semiconductors, but little is known about manipulation and decoherence of semiconductor quantum bits. I will describe experiments showing that motional states of electrons bound to donor impurities in currently-available semiconductors can serve as model qubits. We use intense pulses of terahertz radiation to induce coherent damped oscillation ("Rabi oscillation") of the population of the 1s and 2p (m=+1) states of Hydrogenic donors in GaAs. Our observations demonstrate that a quantum-confined extrinsic electron in a semiconductor can be coherently manipulated like an atomic electron even while sharing space with, in this case, ~10^5 atoms in its semiconductor host. I will conclude by sketching a proposed method to implement a quantum logic gate in which photons in a terahertz cavity are used to couple spatially-separated semiconductor qubits.