Solid State Quantum Computing Using Spectral Holes
  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. 
M.S. Shahriar, P.R. Hemmer, S. Lloyd, J.A. Bowers, A.E. Craig