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Experiments and ideas in trapped ion cavity QED

David Leibrandt, MIT

(Session : Thursday from )

Abstract. Cavity QED is one of the oldest integrated atomic systems, consisting of one or more atoms coupled to the quantized mode of an optical resonator, and it has exciting new applications in laser cooling and quantum information processing. Recent experiments with neutral atoms in optical microresonators have demonstrated sub-Doppler cooling, single photon generation and storage, and coherent mapping between single atom and single photon states. The strong confinement and localization of trapped ions offers the potential for cavity cooling to the motional ground state and improved coherence times for single photon storage and quantum information processing, but so far trapped ion cavity QED experiments have made less progress than their neutral counterparts. This is in large part because it is difficult to make a cavity with a small enough mode volume to achieve strong coupling without the dielectric mirrors distorting the electric field of the ion trap. This work explores some new ideas for trapped ion cavity QED experiments in the single ion weak coupling regime. Because these experiments do not require strong coupling, we can use macroscopic optical resonators which do not interfere with the ion trap electric field. The first part of the talk describes an experiment in progress which has demonstrated resolved sideband cavity cooling of single trapped strontium ions. The ion is confined in a linear RF Paul trap, and we use a 5 cm long, near-confocal Fabry-Perot cavity near the strontium 422 nm optical dipole transition. The cooperativity of 0.25 allows for a theoretical cavity cooling limit of 3 motional quanta, which is slightly lower than the Doppler cooling limit for strontium on the 422 nm transition. The second part of the talk presents an experimental proposal which uses several cold trapped ions in the collective strong coupling regime to achieve a coherent mapping between single ion and single photon states.

Resolved sideband cavity cooling of 88Sr+

David Leibrandt, MIT

(Session 5 : Friday from 5:00-7:00)

Abstract. Cavity cooling is a method of laser cooling which uses coherent scattering into an optical cavity to cool particles [PRL 84, 3787 (2000)]. The particle to be cooled is placed in an optical cavity and excited with a laser tuned to the red of the cavity resonance. On average, scattering events which remove a photon from the laser and put it into the optical cavity cool the particle. The cooling limit is determined by the linewidth and cooperativity of the cavity, which can be designed to allow sub-Doppler cooling. Furthermore, because the cooling limit is independent of the energy level structure of the particle, cavity cooling is in principle applicable to particles without closed optical transitions [PRL 99, 073001 (2007); PRA 77, 023402 (2008)]. In this work we describe an experiment to study cavity cooling of a single 88Sr+ ion in the previously unexplored resolved sideband regime. The ion is confined in a linear RF Paul trap with motional frequencies of 0.86, 1.2, and 1.5 MHz. Large cavity cooling rates are attained by cooling near the 422 nm S1/2 to P1/2 optical dipole transition. We use a 5 cm long, near-confocal Fabry-Perot cavity with a linewidth of 164 kHz and a cooperativity of 0.25. The theoretical cavity cooling limit is 3 motional quanta, which is slightly lower than the Doppler cooling limit for 88Sr+ on the S1/2 to P1/2 transition. Experimental results demonstrate resolved sideband cavity cooling, but with a cavity cooling rate which is several times smaller than predicted by the theory.