Unconventional control of quantum systems with ion traps
Dr. Joseba Alonso (Institute for Quantum Electronics, ETH Zurich, Switzerland)

Surface-electrode ion-traps have been recognized as a promising platform to scale up trapped-ion systems for quantum computation and simulation. To make use of the quantum properties of trapped ions, it is essential to control both the ions' motional and electronic states. In our surface-electrode ion-trap system, we have implemented nano-second electronic switches inside the 4 Kelvin vacuum system to realize quasi-instantaneous “bang-bang” control of the motional states of trapped-ion oscillators. By switching between spatially displaced trapping potentials, we have demonstrated large coherent states with up to 10,000 quanta of energy [1]. With a similar scheme, we are working towards squeezing the ion's motional state as well as fast ion transportation [2]. In the same apparatus, we have recently developed the capability to perform universal logical gates on qutrits formed by three of the electronic energy levels of our ions. While benchmarking control, we have carried out contextuality tests with a single qutrit, demonstrating the violation of non-contextual hidden-variable inequalities as predicted by quantum mechanics [3].

[1] J. Alonso, F. M. Leupold, Z. U. Soler, M. Fadel, M. Marinelli, B. C. Keitch, V. Negnevitsky, and J.
P. Home. Generation of large coherent states by bang-bang control of a trapped-ion oscillator. Nature Communications 7, 11243 (2016).

[2] J. Alonso, F. M. Leupold, B. C. Keitch, and J. P. Home. Quantum control of the motional states of trapped ions through fast switching of trapping potentials. New Journal of Physics 15, 023001 (2013).

[3] A. A. Klyachko, M. A. Can, S. Binicioglu, and A. S. Shumovsky. Simple test for hidden variables in spin-1 systems. Physical Review Letters, 101(2), 020403 (2008).