Fidelity of optimally controlled quantum gates with randomly coupled multiparticle environments

Abstract

This work studies the feasibility of optimal control of high-fidelity quantum gates in a model of interacting two-level particles. One particle (the qubit) serves as the quantum information processor, whose evolution is controlled by a time-dependent external field. The other particles are not directly controlled and serve as an effective environment, coupling to which is the source of decoherence. The control objective is to generate target one-qubit gates in the presence of strong environmentally-induced decoherence and under physically motivated restrictions on the control field. It is found that interactions among the environmental particles have a negligible effect on the gate fidelity and require no additional adjustment of the control field. Another interesting result is that optimally controlled quantum gates are remarkably robust to random variations in qubit-environment and inter-environment coupling strengths. These findings demonstrate the utility of optimal control for management of quantum-information systems in a very precise and specific manner, especially when the dynamics complexity is exacerbated by inherently uncertain environmental coupling.

Acknowledgements

This work was supported by the ARO-QA, DOE, and NSF. DAL was supported by ARO-QA Grant No. W911NF-05-1-0440 and NSF Grant No. CCF-0523675. IAW acknowledges support by the UK QIP IRC funded by EPSRC, and the EC under the Integrated Project QAP funded by the IST directorate as Contract No. 015848.

Notes

†In the case of zero inter-environment coupling, c = 0, all zero values of are left unchanged.