Trapped ions freeze into crystal arrays due to the long range Coulomb repulsion between their charges. However, because these ions have an internal atomic structure, they also poses electric and magnetic dipole moments. In this talk I will review two recent experiments in which the (extremely weak) magnetic and electric dipolar interactions were measured in between trapped ions in a linear crystal. In the first experiment, resonant electric dipole-dipole interactions were measured during photon scattering on an allowed optical dipole transition in chains of up to eight ions. The resonance frequency of the transition was shown to slightly (10’s of kHz) shift whenever the separation between ions equaled an integer number of photon wavelength in what is known as collective Lamb shift . This shift is due to emission and re-absorption of virtual photons between different ions in the chain, and is closely related to superradiance. In the second experiment, the magnetic spin-spin interaction between two trapped ions was observed to lead to the entanglement of their collective spin state. The measurement of this ultra-weak (mHz) interaction strength was made possible by restricting their spin evolution to a decoherence-free subspace. Since the magnetic moment of the ion is equal to that of a single electron, this measurement was used to bound the coupling of electron spin to hypothetical very-light force-mediators that extend the standard model of particle physics [2,3].
 Z. Meir, O. Schwartz, E. Shahmoon, D. Oron and R. Ozeri, Phys. Rev. Lett. 113, 193002 (2014)
 S. Kotler, N. Akerman, N. Navon, Y. Glickman and R. Ozeri, Nature 510, 376 (2014)
 S. Kotler, R. Ozeri, and D. J. Kimball, Phys. Rev. Lett. 115, 081801 (2015)
Reception in the Hbar at 3:30 pm