Schmidt, Piet

Date:   Friday, Apr. 5, 2019
Time:   13:00
Place:   ETH Zurich, Hönggerberg, HPF G 6
Host:    Jonathan Home

Quantum Logic Spectroscopy of Highly Charged Ions

Piet O. Schmidt
QUEST Institute for Experimental Quantum Metrology Physikalisch-Technische Bundesanstalt and Leibniz Universität Hannover, Germany

Outer electrons in highly charged ions (HCI) show extreme properties in comparison to those of atoms. Their narrow optical fine-structure transitions have smaller polarizabilities and electric quadrupole moments, but much stronger relativistic, QED and nuclear size contributions to their binding energy. Consequently, they have been proposed as future clock candidates and to probe for physics beyond the Standard Model. Specifically, HCI offer the most sensitive transitions of any known atomic system to a change in the fine-structure constant [1]. HCI can readily be produced and stored in an electron beam ion trap (EBIT). There, the most accurate laser spectroscopy on any HCI was performed on the 17 Hz wide fine-structure transition in Ar¹³⁺ with 400 MHz resolution, limited by Doppler broadening in the EBIT. The lack of a suitable optical transition for laser cooling and detection can be overcome through sympathetic cooling with a co-trapped Be⁺ ion [2]. Techniques developed for quantum information processing with trapped ions can be used to perform quantum logic spectroscopy [3]: A series of laser pulses transfers the internal state information of the Ar¹³⁺ ion after spectroscopy onto the Be+ ion for efficient readout.

I will present how HCI can be extracted from a compact EBIT [4], charge-to-mass selected and injected into a cryogenic Paul trap containing a crystal of laser-cooled Be⁺ ions. By removing excess Be⁺ ions, a crystal composed of a Be⁺/Ar¹³⁺ ion pair can be obtained. First results on sympathetic ground state cooling and quantum logic spectroscopy of the Ar¹³⁺ P_1/2-P_3/2 fine-structure transition at 441 nm will be presented, improving the resolution by more than six orders of magnitude. Furthermore, excited state lifetimes and the first high-accuracy measurement of excited state g-factors demonstrate the versatility of the technique to access all relevant atomic parameters.

[1] M. G. Kozlov, M. S. Safronova, J. R. Crespo López-Urrutia, and P. O. Schmidt, "Highly charged ions: Optical clocks and applications in fundamental physics," Rev. Mod. Phys. 90, 045005 (2018).

[2] L. Schmöger, O. O. Versolato, M. Schwarz, M. Kohnen, A. Windberger, B. Piest, S. Feuchtenbeiner, J. Pedregosa-Gutierrez, T. Leopold, P. Micke, A. K. Hansen, T. M. Baumann, M. Drewsen, J. Ullrich, P. O. Schmidt, and J. R. C. López-Urrutia, "Coulomb crystallization of highly charged ions," Science 347, 1233–1236 (2015).

[3] P. O. Schmidt, T. Rosenband, C. Langer, W. M. Itano, J. C. Bergquist, and D. J. Wineland, "Spectroscopy Using Quantum Logic," Science 309, 749–752 (2005).

[4] P. Micke, S. Kühn, L. Buchauer, J. R. Harries, T. M. Bücking, K. Blaum, A. Cieluch, A. Egl, D. Hollain, S. Kraemer, T. Pfeifer, P. O. Schmidt, R. X. Schüssler, C. Schweiger, T. Stöhlker, S. Sturm, R. N. Wolf, S. Bernitt, and J. R. Crespo López-Urrutia, "The Heidelberg compact electron beam ion traps," Review of Scientific Instruments 89, 063109 (2018).