Sympathetic cooling and trapped-ion quantum logic gates*

Motional excitation in a trapped-ion quantum information processor degrades the performance of quantum logic gates. Excitations arise from noise emanating from the electrodes and from shuttling ions. Additional ions of a different species can be used to sympathetically cool qubit ions' motion, re-initializing the ground state while leaving intact quantum information stored in the internal state of a qubit ion. Here, we describe an experimental demonstration of a two-qubit entangling operation implemented after sympathetic cooling. We avoid decoherence during ion transport by using a field-independent hyperfine transition of $^9\rm{Be}^+$ as our qubit. \newline *Weizmann Institute of Science, Israel \newline **Lockheed Martin, CO