Quantum Logic Spectroscopy of Molecular Ions

• Antragsteller: Professor Dr. Piet Oliver Schmidt
• Fachliche Zuordnung: Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
• Förderung: Förderung von 2012 bis 2018
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 214284891

• Erstellungsjahr: 2018

Zusammenfassung der Projektergebnisse

Within the scope of the DFG-project Quantum Logic Spectroscopy of Molecular Ions, we have developed and investigated tools for quantum logic spectroscopy of molecular ions. We have demonstrated sympathetic ground state cooling of a two-ion crystal consisting of a single molecular 24MgH+-ion and a single 25Mg+-ion. The developed technique combines pulsed and quench sideband cooling and does not depend on the specific choice of individual pulse lengths and therefore provides a high stability against variation of experimental parameters, like intensity and pointing fluctuations of the laser. In a collaboration with the group of Philip Russel’s group (MPL Erlangen), we have investigated hollow core photonic crystal fibers for transmission of UV light at 280 nm. Transmission loss as low as 1 dB/m was achieved and no transmission degradation was observed after over 100 hours of operation with 15 mW CW input power. The fibers reduce pointing fluctuations and improve the beam quality of Raman laser beams for high fidelity logic operations. Several of the novel quantum logic spectroscopy techniques are based on determining the motional excitation of trapped ions. We have investigated stimulated Raman adiabatic passage (STIRAP) on a motional sideband which maps motional into spin excitation, irrespective of the initial motional quantum state. The parameter regime for which efficient transfer is possible was determined and agreement between the measurements and density matrix simulations was found. One of these techniques is the newly developed Photon Recoil Spectroscopy (PRS), which relies on detection of recoil from photons absorbed on the spectroscopy transition. The resulting momentum kick is detected on a co-trapped logic ion. We have demonstrated PRS on the 2S1/2 → 2P1/2 in 40 Ca+ . We could show that only around 10 scattered photons are necessary to achieve a signal-to-noise ratio of 1, which makes the technique well-suited for transitions in molecules with nearly diagonal Franck-Condon factors. Photon recoil spectroscopy was used to perform isotope shift measurements in Ca+ ions. Extending the technique to non-closed transitions, we were able to measure the isotope shift of the 2S1/2 → 2P1/2 , the 2S1/2 → 2P3/2 and the 2 D3/2 → 2 P1/2 transition of the even isotopes 42Ca+ , 44Ca+ and 48Ca+ with respect to 40 Ca+ . For all measurements an uncertainty below 100 kHz was achieved, which represents an improvement by up to two orders of magnitude over previous experiments. We extracted the relative and absolute field and mass shift constants with a multi-dimensional King plot analysis of the spectroscopy data. Finally, we have implemented a non-destructive state detection scheme for molecular ions based on quantum logic. We were able to detect black body radiation-induced transitions between rotational states of 24MgH+ and use the detuning dependence of the quantum logic laser to demonstrate a simple version of quantum logic spectroscopy on the X1 Σ+ → A1 Σ+ optical transition. The presented molecular state detection protocol was the first non-destructive rotational state resolving implementation. For the first time quantum logic operations have been performed between an atomic and a molecular ion.

Projektbezogene Publikationen (Auswahl)

• Damage-free single-mode transmission of deep- UV light in hollow-core PCF, Optics Express, Vol. 22, No. 13, (2014)
  F. Gebert, M. H. Frosz, T. Weiss, Y. Wan, A. Ermolov, N. Y. Joly, P. O. Schmidt, and P. St. J. Russell
  
• Precision spectroscopy by photon-recoil signal amplification, Nat Commun 5, 4096 (2014).
  Y. Wan, F. Gebert, J. B. Wübbena, N. Scharnhorst, S. Amairi, I. D. Leroux, B. Hemmerling, N. Lörch, K. Hammerer, and P. O. Schmidt
  
• Efficient sympathetic motionalground-state cooling of a molecular ion. Physical Review A, 91(4):043425, (2015)
  Yong Wan, Florian Gebert, Fabian Wolf, and Piet O. Schmidt
  
• Precision Isotope Shift Measurements in Calcium Ions Using Quantum Logic Detection Schemes. Physical Review Letters, 115(5):053003, (2015)
  Florian Gebert, Yong Wan, Fabian Wolf, Christopher N. Angstmann, Julian C. Berengut, and Piet O. Schmidt
  
• Detection of motional ground state population of a trapped ion using delayed pulses. New Journal of Physics, 18(1):013037, 2016
  F. Gebert, Y. Wan, F. Wolf, Jan C. Heip, and Piet O. Schmidt
  
• Non-destructive state detection for quantum logic spectroscopy of molecular ions. Nature, 530(7591):457– 460, (2016)
  Fabian Wolf, Yong Wan, Jan C. Heip, Florian Gebert, Chunyan Shi, and Piet O. Schmidt
  
• Unexpectedly large difference of the electron density at the nucleus in the 4p 2 P1/2,3/2 fine-structure doublet of Ca+ . Applied Physics B, 123(1):2, January 2017
  C. Shi, F. Gebert, C. Gorges, S. Kaufmann, W. Nörtershäuser, B. K. Sahoo, A. Surzhykov, V. A. Yerokhin, J. C. Berengut, F. Wolf, J. C. Heip, and P. O. Schmidt