Entangled states of trapped atomic ions

Dietrich G. Leibfried

Yiheng Lin, John Gaebler, Florentin Reiter +10 more

We apply laser fields to trapped atomic ions to constrain the quantum dynamics from a simultaneously applied global microwave field to an initial product state and a target entangled state. This approach comes under what has become known in the literature as "quantum Zeno dynamics" and we use it to prepare entangled states of two and three ions. With two trapped ^{9}Be^{+} ions, we obtain Bell state fidelities up to 0.990_{-5}^{+2}; with three ions, a W-state fidelity of 0.910_{-7}^{+4} is obtained. Compared to other methods of producing entanglement in trapped ions, this procedure can be relatively insensitive to certain imperfections such as fluctuations in laser intensity.

Christoph Becher, Jan Benhelm, D. Chek-al-kar +16 more

F. Schmidt-Kaler, R. Gerritsma

We propose detecting the magnetic field gradient produced by the magnetic dipole moment of a single atom by using ions in an entangled state trapped a few μ m from the dipole. This requires measuring magnetic field gradients of order 10 −13 tesla/ μ m. We discuss applications in determining magnetic moments of a wide variety of ion species, for investigating the magnetic substructure of ions with level structures that are not suitable for laser cooling and detection, and for studying exotic or rare ions, and molecular ions. The scheme may also be used for measuring spin imbalances of neutral atoms or atomic ensembles trapped by optical dipole forces. As the proposed method relies on techniques that are well established in ion trap quantum information processing, it is within reach of current technology.

Charles A. Sackett

Shi-Biao Zheng

A scheme is presented for generating entangled states for two atoms in a cavity. In the scheme two atoms simultaneously interact with a cavity mode with a small detuning. The operation time is very short and thus the decoherence can be effectively suppressed. Furthermore, the scheme is valid no matter whether the two atoms have the same coupling strengths or not. The scheme can be used to generate multi-atom W states without the requirement of individual addressing of the atoms, which is also experimentally important. The scheme can also be generalized to produce entangled states in an ion trap without individually addressing the ions.