Bohnet, Justin G.

Thursday Oct 31, 2013
Time: 11:00
Place: ETH Science City, HPF G6
Host: Tobias Donner/ Tilman Esslinger

Atoms cooperating in an optical cavity: Superradiant lasing and spin squeezing

Justin G. Bohnet
University of Colorado at Boulder, JILA

By allowing a large ensemble of laser cooled and trapped atoms to interact collectively with an optical cavity, we have explored two phenomena that may prove useful for enhancing precision measurements: superradiant lasing and spin squeezing.

Superradiant lasers have been proposed as future ultrastable optical frequency references, with predicted linewidths < 1 millihertz.  These lasers operate in an unusual regime of laser physics where collective emission from an atomic ensemble maps the quantum phase stored in the atoms onto the optical cavity field. I will give an overview of our experimental work using a cold-atom, superradiant Raman laser as a model system to confirm a number of the key predictions concerning superradiant lasing, including the possibility of coherent emission with < 1 intracavity photon and greatly reduced sensitivity to cavity frequency pulling.

I will also present our work using cavity-aided, coherence-preserving measurements to generate conditional squeezing of the hyperfine ground states of 87Rb.  Spin squeezing creates entanglement between atoms that result in reduced quantum projection noise, possibly allowing atomic sensors to operate with a lower noise floor or increased bandwidth. I will discuss our latest result utilizing a cycling transition for the quantum non-demolition probe.  Using this new probing scheme, we have effectively eliminated the measurement back-action caused by Raman transitions. We
directly observe, with no background subtraction, a spin squeezed state with sensitivity to measuring a quantum phase enhanced 10.5 times beyond the quantum limit for an unentangled state.