Entangled States of Light and Atoms for Measurements Below the Standard Quantum Limit

Quantum mechanics tells us that both matter and light can exhibit wave-like or particle-like behavior. Devices that use the interference of waves--the fact that waves can cancel each other out or enhance each other--enable highly sensitive measurements of almost anything: time, gravity, motion, or electric and magnetic fields. In particular, atomic clocks, that are based on wave interference, are the most accurate devices ever made by mankind, and have many important technological applications. Clocks and other interferometers operate by measuring many independent atoms in parallel to enhance the signal. The device readout is then subject to measurement noise (projection noise), not unlike the flipping of a collection of coins where the outcome is not always an equal number of heads and tails. Here it is proposed to develop methods to produce correlated states of many atoms (so-called entangled states) that can be used to reduce or eliminate the projection noise. Quantum mechanics allows one to prepare a situation where each coin individually still randomly shows head or tail, but the collection of coins always shows an equal number of heads and tails. By demonstrating the generation of such states, the proposed research program could boost the precision of atomic clocks and other interferometers, with significant implications for timekeeping, navigation, and precision measurements. The proposed work will unite research and educational goals by training graduate students, and by integrating undergraduate students and exceptional high-school students into the research effort.

This project is aimed at the deterministic preparation of non-classical (many-body entangled) states of atomic ensembles and of light fields using collective atom-light interaction enhanced by an optical resonator. Such states can be used to improve the precision of atomic clocks and other atom interferometers beyond the standard quantum limit. The main goals of the project are to demonstrate a non-destructive measurement of the power of a traveling laser beam below the photon shot noise limit, to create Schroedinger cat states or strongly spin squeezed states of a large atomic ensemble via the detection of a single photon, and to use such states to operate an atomic clock below the standard quantum.