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arXiv:quant-ph/0511213 · Physical Review A

Effective cross-Kerr nonlinearity and robust phase gates with trapped ions

F. L. Semião, A. Vidiella-Barranco

Published Dec 16, 2005• 27 citations
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Abstract

We derive an effective Hamiltonian that describes a cross-Kerr-type interaction in a system involving a two-level trapped ion coupled to the quantized field inside a cavity. We assume a large detuning between the ion and field (dispersive limit) and this results in an interaction Hamiltonian involving the product of the (bosonic) ionic vibrational motion and field number operators. We also demonstrate the feasibility of operation of a phase gate based on our Hamiltonian. The gate is insensitive to spontaneous emission, an important feature for the practical implementation of quantum computing.

DOI
10.1103/physreva.72.064305

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A long-lived coherent state and nonlinear interaction have been experimentally demonstrated for the vibrational mode of a trapped ion. We propose an implementation of quantum computation using coherent states of the vibrational modes of trapped ions. Differently from earlier experiments, we consider a far-off resonance for the interaction between external fields and the ion in a bidimensional trap. By appropriate choices of the detunings between the external fields, the adiabatic elimination of the ionic excited level from the Hamiltonian of the system allows for beam splitting between orthogonal vibrational modes, production of coherent states, and nonlinear interactions of various kinds. In particular, this model enables the generation of the four coherent Bell states. Furthermore, all the necessary operations for quantum computation, such as preparation of qubits and one-qubit and controlled two-qubit operations, are possible. The detection of the state of a vibrational mode in a Bell state is made possible by the combination of resonant and off-resonant interactions between the ion and some external fields. We show that our read-out scheme provides highly efficient discrimination between all the four Bell states. We extend this to a quantum register composed of many individually trapped ions. In this case, operations on two remote qubits are possible through a cavity mode. We emphasize that our remote-qubit operation scheme does not require a high-quality factor resonator: the cavity field acts as a catalyst for the gate operation.
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A trapped ion in a cavity can simultaneously interact with a laser field as well as the cavity field. Based on the point, we propose a new scheme to implement quantum logic gates such as single qubit rotation gate, two qubit controlled-phase gate and controlled-NOT gate. and scheme employs the model used in literature [10-12] and is different from these works because computation basis is composed by the internal ionic state and motional state. We also discussed the experimental requirement for our scheme.