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A: Fachverband Atomphysik

A 16: Ultra-Cold Atoms: Single Atoms (with Q)

A 16.1: Gruppenbericht

Mittwoch, 10. März 2010, 16:30–17:00, A 320

Real-time feedback control of a single atom trajectory — •Alexander Kubanek, Markus Koch, Christian Sames, Alexei Ourjoumtsev, Pepijn Pinkse, Karim Murr, and Gerhard Rempe — Max-Planck-Institut für Quantenoptik, Garching, Germany

Feedback is a general, well developed technique, which provides an important tool to control classical systems in a wide variety of fields. Novel features arise when transferring the idea of feedback into the quantum domain, e.g. to engineer non-trivial quantum states. An interesting question is whether one can influence quantum trajectories by measurement and feedback without violating Heisenberg uncertainty relations. A prerequisite for this is to measure and react in real time with a minimum measurement rate and, hence, disturbance.

By combining the arsenal of cavity QED techniques with blue-light trapping we have now achieved a longstanding goal, namely the real-time feedback control on the motion of a single atom. The feedback acts on a time scale that is 70 times faster than the typical time for the evolution of the centre of mass of the atom. Individual probe photons carrying information about the atomic position activate a dipole laser that steers the atom towards or away from the cavity centre. Depending on the specific implementation, the trapping time is increased by a factor of more than four and the localisation of the atom improved owing to feedback cooling. Such a feedback technique teaches us that one can control an apriori unpredictable atomic trajectory, and marks a step towards the exploration of quantum trajectories.

A. Kubanek, et al., Nature, in press (2009)