München 2004 – scientific programme

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Q: Quantenoptik und Photonik

Q 11: Fallen und Kühlung

Q 11.8: Talk

Monday, March 22, 2004, 18:15–18:30, HS 224

Real-time measurement of a single ion trajectory — •Pavel Bushev, Alex Wilson, Jürgen Eschner, and Rainer Blatt — Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria

In our experiment a single Ba⁺ ion is held by a Paul trap and continuously Doppler cooled with a laser. The residual thermal motion of the ion in the trap has an average amplitude of about 35 nm at a frequency of 1 MHz. A collimating lens and a distant mirror are placed such that part of the scattered light is retro-reflected, thus leading to interference of high contrast. Hence, the phase of the interference fringes are sensitive to the ion-mirror distance [1]. In this case the photocurrent contains all the information about the ion’s motion. Its amplitude and phase are detected with a high signal-to-noise-ratio.

By using a phase-locking technique we are able to observe the ion trajectory with an accuracy of 10 nm within a measurement time of 10 ms. We also report first attempts to cool a single atomic particle (the Ba⁺ ion), beyond the Doppler-cooling-limit using electronic feedback. We create an additional friction force, which is proportional the No-dqinstantaneous speedNo-dq of the ion in the trap, by supplying additional electric fields along the direction of the ion’s motion. A dip in the motional spectrum appears when this external friction force is applied.

[1] J. Eschner et al., Nature 413, 495-498, (2001)