  A quantum computer that stores information on two-state systems called
quantum bits or qubits must be able to address and manipulate individual
qubits, to effect coherent interactions between pairs of qubits, and to read
out the value of qubits.1,2 Current methods for addressing qubits are divided
up into spatial methods, as when a laser beam is focused on an individual
qubit3,4,5 or spectral methods, as when a nuclear spin in a molecule is
addressed using NMR.6,7 The density of qubits addressable spatially is limited
by the wavelength of light, and the number of qubits addressable spectrally is
limited by spin linewidths. Here, we propose a method for addressing qubits
using a method that combines spatial and spectral selectivity. The result is a
design for quantum computation that provides the potential for a density of
quantum information storage and processing many orders of magnitude greater
than that afforded by ion traps or NMR. Specifically, this method uses an
ensemble of spectrally resolved atoms in a spectral holeburning solid. The
quantum oupling is provided by strong atom-cavity interaction. Using a thin
disc of diamond containing nitrogen-vacancy color centers as an example, we
present an explicit model for realizing up to 300 coupled qubits in a single
spot. We show how about 100 operations can take place in parallel, yielding
close to 40,000 operations before decoherence.
