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Mesoscopic cold atomic ensembles

Quantum limited control of mesoscopic atomic states for precision measurements and communication.

Entangled atomic states, such as they are found in spin squeezed cold atomic clouds, allow for spectroscopic measurements beyond the standard quantum limit and are of particular interest for state-of-the-art optical lattice clocks and atomic field sensors.

We use ensembles of a few thousand cold atoms and manipulate their quantum state by interaction with light.

The collective quantum state of atoms is entangled with a light pulse emerging from the ensemble; by measuring the optical state and its quantum fluctuations, quantum noise limited measurements of the atomic state can be performed: optically dense atomic ensembles can be used for metrology as sensitive sensors or as precise clocks!

Currently we are operating two experiments.

The clock-experiment

We trap a laser-cooled ensemble of $\approx 100000$ Cesium atoms in a dipole trap and use dispersive bichromatic quantum-non-demolition measurements to manipulate and to characterize collective entangled states of the ensemble. The primary goal of this experiment is to improve precision for atom-based metrology and to create non-Gaussian states.

The Nanofiber-experiment

In a collaboration with the group of A. Rauschenbeutel we produced a tapered nano fiber. Using such a setup high optical depths can be achieved with only a few thousand atoms. This allows for using the atoms as a sensor with an high lateral resolution defined by the tight confinement along the fiber. To use fewer atoms while still having a stronger coupling to light fields is more favorable for controlling the atomic quantum fluctuations with QND measurements in the presence of classical noise sources.