  A solid-state quantum computer with dipolar coupling between qubits is
proposed. The qubits are formed by the low-lying states of an isolated acceptor
in silicon. The system has the scalability inherent to spin-based solid state
systems, but the spatial separation between the qubits is an order of magnitude
larger. Despite strong dipolar inter-qubit coupling, the decoherence rate, as
measured by electric dipolar echoes at an energy splitting of 1.5 GHz, is less
than 1 kHz at low temperatures. For inter-acceptor distances of 100 nm and for
modest microwave field amplitudes (50 V/cm) the clock frequency of the quantum
computer is 0.1 GHz, which yields a quality factor of 105. This paper describes
ideas for detection and operation of the quantum computer, and examines
limitations imposed by noise sources.
