Weak measurement based feedback control of atomic ensembles (Orale)

Abstract

Atom interferometry based sensors provide today the most precise measurements of time, inertial forces and magnetic fields. In the common approach, a superposition state is interrogated for a given time interval and finally destructively measured. Conversely, we can repeatedly probe non-destructively the same quantum system and demonstrate efficient measurement schemes using feedback. First, we protect a spin polarized atomic ensemble from the decoherence induced by a synthetic noise. After the noise action, the state of the atomic system is read out with negligible projection using a non-destructive probe, and later corrected with a coherent manipulation to restore the initial state. The efficiency of the feedback scheme is studied versus the strength of the measurement and a maximum is found from the trade-off between information gain and probe destructivity. Our feedback controller is then applied to stabilize a classical local oscillator on a collective quantum state, and this is used in an atomic clock configuration to demonstrate experimentally that in some contexts a hybrid phase and frequency lock can surpass conventional atomic clocks which rely only on a frequency lock