Quantum Logic with Composite Pulse Sequences on $Sr^+$

The optical $5S_{1/2} \rightarrow 4D_{1/2}$ transition in $Sr^+$ is an attractive qubit because it can be addressed by diode lasers, which are relatively inexpensive and easy to operate. We characterize single-qubit rotations as well as a CNOT gate on a $Sr^+$ ion in a surface electrode Paul trap. To improve these operations, the frequency of the clock laser is stabilized to a high-finesse optical cavity. The resulting linewidth of the laser is approximately 300Hz. Composite pulse sequences, a technique adapted from NMR, have been shown to reduce the effects of systematic errors in a variety of quantum systems. We demonstrate several composite sequences that improve the fidelity of quantum logic operations on $Sr^+$.