Electrodynamically trapped Yb + ions for quantum information processing

When investigating fundamental questions related to quantum mechanics, experiments are called for where individual quantum systems can be accessed and deterministically manipulated. The interaction of trapped atomic ions among themselves and with their environment can be controlled to a high degree of accuracy, and thus allows for the preparation of well-defined quantum states of the ions’ internal and motional degrees of freedom. Trapped ions have proven to be well suited for a multitude of investigations, for instance, into entanglement, decoherence, and quantum information processing, and for applications such as atomic frequency standards. Quantum information processing, in particular, requires the accurate and precise control of internal and often of motional quantum dynamics of a collection of trapped ions. In order to eliminate sources of possible errors, and thus prepare the ground to attain the ambitious goal of using trapped ions for large-scale quantum computing or quantum simulations, it is desirable to simplify the apparatus used for such experiments as far as possible. An unprecedented degree of control of quantum systems has been reached in recent experiments with trapped ions, for instance, with Be + 1 ,C a + 2, and Cd + 3 ions. Mainly the type of ion used in such experiments determines the experimental infrastructure needed for the controlled manipulation of these ions. The available ionic transitions, for instance, determine the radiation sources to be used: In Ca + , an optical electric quadrupole transition has been used as a qubit leading to a coherence time ultimately limited by spontaneous radiative decay. More importantly, phase fluctuations of the laser light driving the qubit transition limit the available coherence time, even when using a highly sophisticated light source 5. Phase fluctuations of the radiation driving the qubit transition do not present a major obstacle, if a hyperfine transition is used as a qubit as, for instance, in Be + or Cd + , since such a transition is usually excited by a stimulated two-photon Raman process where only relative fluctuations between the two driving fields limit the available coherence time. Choosing magnetic field insensitive states as a qubit, as was demonstrated recently with Yb + 4 and Be + 6, may further contribute to achieving the desired long co