Atom interferometers are extremely precise measurement devices for quantities such as time, inertial forces, and electromagnetic fields. When operated with an ensemble of uncorrelated (non-entangled) particles, interferometers are fundamentally limited by shot noise, giving rise to the standard quantum limit (SQL) of interferometric measurement. State-of-the-art devices operate at this limit. Recent proof-of-principle experiments have shown that the SQL can be overcome using many-particle entangled states in the interferometer. Such quantum metrology can potentially lead to significant improvements in interferometer sensitivity. At the same time, it provides new insights into the elusive nature of many-particle entanglement.

I will discuss the physics behind the standard quantum limit and how it can be overcome using entangled states. In a recent experiment, we have realized an atom interferometer operating with an uncertainty of 4.0 dB below the SQL. Our interferometer employs entangled atoms in a spin-squeezed Bose-Einstein condensate and maintains performance below the SQL for Ramsey interrogation times up to 20 ms. Quantum-state tomography is used to characterize the interferometer input state, revealing a depth of entanglement of more than 40 particles. Using an atom chip, we spatially scan the atoms over tens of micrometers while maintaining sub-SQL operation. We use this scanning capability to perform a spatially resolved measurement of microwave fields from an integrated circuit. These techniques are promising for high-resolution imaging of electromagnetic fields near solid-state microstructures.

References:

R. Schmied and P. Treutlein, New J. Phys. 13, 065019 (2011).

M. F. Riedel, P. Böhi, Yun Li, T. W. Hänsch, A. Sinatra, and P. Treutlein, Nature 464, 1170 (2010).

Radiation pressure has fascinated scientists for centuries. In 1619, Johannes Kepler postulated the existence of radiation pressure to explain why comet tails always point away from the Sun. The idea behind this early proposal, which considered light to be composed of small particles, is in agreement with our current understanding of light forces; light carries both linear and angular momenta, and can transfer energy to atoms, molecules and particles. This fact allows radiation pressure to accelerate or push small particles in the direction of the light flow.

The idea of using optical beams to attract objects is much less trivial and has long been a dream of scientists and the public alike. Over the years, a number of proposals have attempted to bring this concept to life. Here we review the most recent progress in this emerging field, including new concepts for manipulating small objects using optically induced ‘negative forces’, achieved by tailoring the properties of the electromagnetic field, the environment or the particles themselves [1]

[1] A. Dogariu, S. Sukhov and J.J.  Sáenz,  Nature Photonics 7, 24-27 (2013).