T. Dubielzig

We report on the implementation of arbitrary circuits on a universal two-qubit register that can act as the computational module in a trapped-ion quantum computer based on the quantum charge-coupled device architecture. A universal set of quantum gates is implemented on a two-ion Coulomb crystal of $^9$Be$^+$ ions using only chip-integrated microwave addressing. Individual-ion addressing is implemented using microwave micromotion sideband transitions; we obtain upper limits on addressing cross-talk in the register. Arbitrary two-qubit operations are characterized using the cycle benchmarking protocol.

Individual-qubit readout is a key ingredient for quantum simulation and quantum computation. Furthermore, this readout must take place in real-time to enable the application of quantum error-correction protocols. In this paper the capability of an EMCCD camera with a real-time processing capable output is demonstrated to determine the quantum state of a single $^9$Be$^+$ ion and the required timing sequences are explored. The results are comparable to a PMT based detection. Experiments on the individual detection of $^9$Be$^+$ qubit states undergoing coherent excitation are reported. Sources of error and the amount of crosstalk in the detection system are discussed. Error rates due to known problems in the state preparation and measurement processes were determined to be approximately 0.5 %.