# Modern Quantum Technology with trapped Ions

### Monday, 24 Nov. 2014, 17:30 - 19:00

**Presenter:** Ferdinand Schmidt-Kaler

**Host:** Markus Arndt

**Where:** Lise-Meitner-Hörsaal, 1. Stck, Strudelhofgasse 4, Wien

**Modern Quantum Technology with trapped Ions**

The quantum states of ions are perfectly controlled, and may be used for fundamental research in quantum physics, as highlighted by the Nobel Prize given to Dave Wineland in 2012. While trapped ions are among the most promising implementations for a furure quantum computer, and single trapped ions have shown beautiful proofs to serve as atomic clocks, we identify novel directions of quantum technologies, which have high impact on solid state physics. The talk will be focused to those appraoches which we follow in the Mainz group:

I) The delivery of single cold ions-on-demand for the deterministic doping of solid state materials with nm spatial precision to generate design-structures optimized for quantum processors: Using single ejected Ca^{+} ions we reach 8nm wide spot, which can be used for imaging [1]. Co-trapped N_{2}^{+} ions have been ejected, this will lead to the fabrication of arrays of NV center in diamond [2], well suited for solid state quantum processors. The approach is not limited to this specific materials but may serve equally well to implant single Phosphorous qubits in Silicium.

II) On the conceptual side, phase transitions, universal laws of defect formation and non-linear interactions in a solid can be mimicked with trapped ions: Control parameters may be tailored such that a structural phase transition from a linear to a zigzag configuration of the crystal is crossed [3]. Trapped ions serve here as a clean model system to investigate universal laws of defect formation when such transition is crossed fast and causally separated regions form [4]. The amount of defects is predicted by the Kibble-Zurek mechanism [5]. We have experimentally determined the universal scaling exponent for defect formation and confirm the scaling law for the inhomogeneous Kibble-Zurek effect accurately at the percent level [6].Next steps are studies of the Peierls Nabarro potential which keeps defects trapped in the crystal. Approaching the phase transition at the critical point is leading to large non-linear interactions of in the ion crystal normal modes. I will show how the application of multi-dimensional spectroscopy allows to determine effects such as cross-Kerr coupling or resonant coupling between vibrational modes [7], non-linear effects well known in non-linear optics.

[1] Jakob et al., arXiv:1405.6480

[2] Schnitzler et al., Phys. Rev. Lett. 102, 070501 (2009)

[3] Kaufmann et al., PRL 109, 263003 (2012)

[4] Kibble, Jour. Phys. A 9, 1387 (1976), Zurek, Nat. 317, 505 (1985), Del Campo & Zurek, arXiv:1310.1600

[5] Del Campo et al. PRL 105, 75701 (2010), De Chiara et al. NJP 12, 115003 (2010)

[6] Ulm et al., Nat. Comm.4, 2290 (2013)

[7] Lemmer et al, arXiv:1407.1071