P. Ivanov, U.G. Poschinger, K. Singer, F. Schmidt-Kaler
Europhysics Letters 92, 30006 (2010)
http://arxiv.org/abs/0909.5397
We propose a geometric phase gate in a decoherence-free subspace with trapped ions. The quantum information is encoded in the Zeeman sublevels of the ground-state and two physical qubits to make up one logical qubit with ultra long coherence time. Single- and two-qubit operations together with the transport and splitting of linear ion crystals allow for a robust and decoherence-free scalable quantum processor. For the ease of the phase gate realization we employ one Raman laser field on four ions simultaneously, i.e. no tight focus for addressing.