Spatially Homogeneous Entanglement for Matter-Wave Interferometry   Created with Time-Averaged Measurements
  We demonstrate a method to generate spatially homogeneous entangled, spin-squeezed states of atoms appropriate for maintaining a large amount of squeezing even after release into the arm of a matter-wave interferometer or other free space quantum sensor. Using an effective intracavity dipole trap, we allow atoms to move along the cavity axis and time average their coupling to the standing wave used to generate entanglement via collective measurements, demonstrating 11(1) dB of directly observed spin squeezing. Our results show that time averaging in collective measurements can greatly reduce the impact of spatially inhomogeneous coupling to the measurement apparatus. 
Kevin C. Cox, Graham P. Greve, Baochen Wu, and James K. Thompson
physics.atom-ph quant-ph