Ch. Piltz, B. Scharfenberger, A. Khromova, A. F. Varón, Ch. Wunderlich
Quantum information science has grown into an interdisciplinary research field encompassing the investigation of fundamental questions of quantum physics, metrology as well as the quest for a quantum computer, or quantum simulator. The latter would allow unprecedented insight into scientific prob- lems relevant, for instance, for physics and chemistry . In order to exploit the principles of quantum physics for such purposes, it is necessary to preserve quantum coherence while carrying out gate operations. Dynamical decoupling (DD) was successfully employed to extend the coherence time of quantum states and for single-qubit operations. Here, we demonstrate for the first time a universal conditional two-qubit quantum gate whose coherent dynamics is protected by DD pulse sequences. The sequences employed here are robust against imperfections of DD pulses that otherwise may destroy quantum information or interfere with gate dynamics. A Controlled-NOT gate is implemented, despite the gate time being more than one order of magnitude longer than the intrinsic coherence time of the system. These experiments are carried out using a well-controlled prototype quantum system - trapped atomic ions coupled by an effective spin-spin interaction. The scheme for protecting conditional quantum gates demonstrated here is applicable to other physical systems, such as nitrogen vacancy centers, solid state nuclear magnetic resonance, and circuit quantum electrodynamics.
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http://arxiv.org/abs/1208.2204
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