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Trapped Ions

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We are an experimental group working with laser-cooled atomic ions confined in electromagnetic traps. We develop two main research topics:
- the design, fabrication and test of surface micro traps devoted to quantum information
- the study of large ensembles of cold ions (Coulomb crystals) containing different species

Surface micro traps

Microfabricated surface-electrode ion traps, invented in 2004 [1] and demonstrated for the first time in 2006 [2], constitute one of the most promising systems in the prospect of constructing an "useful" quantum computer [3]. In such devices the electromagnetic field that traps the ions is generated by an electrode set lying in the same plane (the substrate). The ions are trapped at a distance d from the surface, which approximately coincides with the transverse size of the electrodes. This geometry has two assets: it is easily implemented by cleanroom microfabrication techniques and allows for analytical calculations of trapping potentials [4].
A major interest of these devices is the capability to address hyperfine transition sensitive to ion motion (sidebands) with near-field microwaves generated on chip [5].

Electron microscopy image of a Gold on Silica microtrap device
MPQ/IPIQ

We build and operate miniaturized scalable devices with the aim of of performing elementary quantum logic operations, a major challenge in experimental quantum information science. In particular, we study and address the "anomalous heating" phenomenon: as the dimension of devices decreases, the observed heating rates for the ion motion increase at such a rate that the fidelities of quantum gates become too small in devices smaller than 40 µm [6]. Such a phenomenon is related to the surface quality of the electrodes and will be studied through a multidisciplinary approach (collaboration with the STM group in the MPQ laboratory, specialized in surface science).

[1] J. Chiaverini et al., Quant. Inf. Comput. 5, 419 (2005).
[2] S. Seidelin et al., Phys. Rev. Lett. 96, 253003 (2006).
[3] D. Kielpinski et al., Nature 417, 709 (2002).
[4] M. G. House, Phys. Rev. A 78, 033402 (2008).
[5] C. Ospelkaus et al., Phys. Rev. Lett. 101, 090502 (2008).
[6] Q. A. Turchette et al., Phys. Rev. A 61, 063418 (2000).

Multi species Coulomb crystals

Several species of ions can be present at the same time in an ion trap. In that case Coulomb interaction allows for an efficient redistribution of kinetic energy among the species. If one of the species is laser-cooled, the ensemble can be "sympathetically cooled" down to milliKelvin translational temperatures [1]. Taking advantage of this feature it is possible to obtain cold samples of atomic or molecular ions that cannot be directly laser-cooled but have interesting features, for example for metrology purposes [2]. In the special case of ion strings composed by only two different ions, the control of the (common) state of motion at a quantum level opens the way to applications to quantum information [3] and to the optical frequency metrology (quantum logic spectroscopy) [4].

Ion Coulomb crystal containing the four natural isotopes of Sr+
MPQ/IPIQ

In linear Paul traps, the transverse stiffness depends on the mass of the ion. Therefore in large cold ion ensembles spatial segregation arises that confines lighter species nearer to the axis of the trap. This property, combined with radiation pressure exerted by cooling lasers, allows for the quantitative control of the composition in multi-component ion Coulomb crystals. These systems, in which one specie can be addressed in the absence of perturbations induced by laser cooling have been used in our group for spectroscopic measurements [5]

[1] P. Bowe et al., Phys. Rev. Lett. 82, 2071 (1999).
[2] P. Blythe et al., Phys. Rev. Lett. 95, 183002 (2005).
[3] J. P. Home et al., Science 325, 1227 (2009).
[4] C. W. Chou et al., Science 329, 1630 (2010).
[5] B. Dubost et al., Phys. Rev. A 89, 032504 (2014).