Abstract

We trap ions in a linear micro segmented Paul-trap for the purpose of quantum information processing. Qubits are encoded in magnetic sublevels of the ground state of Ca+ and manipulated with laser light near 729 nm from a TiSa laser. A stable light source is essential to achieve long coherence times, which are necessary for storing quantum information in a qubit. The frequency stabilization is performed by locking the laser to an ultra-stable Fabry-Pérot resonator using a Pound-Drever-Hall error signal and fast electronics. The quality of the lock can be determined from a beat note with another laser at 729 nm. Additionally, a spin-echo sequence on the calcium ion allows to achieve a value of the laser linewidth and the resulting qubit coherence time. We have separated the contribution of the magnetic field fluctuations on the coherence time by interrogating transitions with different susceptibility to the ambient magnetic field. A possibility of extending the coherence time is demonstrated using a spin-lock technique