RESUMEN
We demonstrate how to use feedback to control the internal states of trapped coherent ensembles of two-level atoms, and to protect a superposition state against the decoherence induced by a collective noise. Our feedback scheme is based on weak optical measurements with negligible backaction followed by coherent microwave manipulations. The efficiency of the feedback system is studied for a simple binary noise model and characterized in terms of the trade-off between information retrieval and destructivity from the optical probe. We also demonstrate the correction of more general types of collective noise. This technique can be used for the operation of atomic interferometers beyond the standard Ramsey scheme, opening the way towards improved atomic sensors.
RESUMEN
Thirty-eight normal volunteers were tested in an ambulance car while being accelerated in one of the following positions: (1) sitting upright facing forward in the car, (2) lying supine on a stretcher head forward, (3) supine position head backward. Consecutive short period of negative horizontal acceleration (0.7-0.95 g) were achieved by brisk braking manoeuvres of the car, followed by weak reacceleration (0.15 g). Motion sickness symptoms were observed and recorded after each experiment using a special motion sickness scaling index which was weighted according to the strength of any particular symptom. The results indicate that horizontal linear acceleration in a car, such as experienced during multiple breaking manoeuvres, is an effective motion sickness provoking stimulus. Negative X-axis stimulation is more nauseogenic then acceleration in the Z-axis stimulation is more nauseogenic then acceleration in the Z-axis of the body.
