Two mode coupling in a single ion oscillator via parametric resonance
  Atomic ions, confined in radio-frequency Paul ion traps, are a promising candidate to host a future quantum information processor. In this letter, we demonstrate a method to couple two motional modes of a single trapped ion, where the coupling mechanism is based on applying electric fields rather than coupling the ion's motion to a light field. This reduces the design constraints on the experimental apparatus considerably. As an application of this mechanism, we cool a motional mode close to its ground state without accessing it optically. As a next step, we apply this technique to measure the mode's heating rate, a crucial parameter determining the trap quality. In principle, this method can be used to realize a two-mode quantum parametric amplifier. 
Dylan J Gorman, Philipp Schindler, Sankaranarayanan Selvarajan, Nikos   Daniilidis, Hartmut H\"affner
quant-ph physics.atom-ph