



01532nas a2200193   4500008004100000245009300041210006900134260001500203300001100218490000800229520089100237100002101128700002401149700002201173700002301195700002401218700002301242856007301265       2018                        eng d00aRobust two-qubit gates in a linear ion crystal using a frequency-modulated driving force0 aRobust twoqubit gates in a linear ion crystal using a frequencym  c2018/01/09  a0205010 v1203 a<p>In an ion trap quantum computer, collective motional modes are used to entangle two or more qubits in order to execute multi-qubit logical gates. Any residual entanglement between the internal and motional states of the ions will result in decoherence errors, especially when there are many spectator ions in the crystal. We propose using a frequency-modulated (FM) driving force to minimize such errors and implement it experimentally. In simulation, we obtained an optimized FM gate that can suppress decoherence to less than 10&minus;4 and is robust against a frequency drift of more than &plusmn;1 kHz. The two-qubit gate was tested in a five-qubit trapped ion crystal, with 98.3(4)% fidelity for a Mølmer-Sørensen entangling gate and 98.6(7)% for a controlled-not (CNOT) gate. We also show an optimized FM two-qubit gate for 17 ions, proving the scalability of our method.</p>1 aLeung, Pak, Hong1 aLandsman, Kevin, A.1 aFiggatt, Caroline1 aLinke, Norbert, M.1 aMonroe, Christopher1 aBrown, Kenneth, R.  uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.020501