Spin dynamics allows for the generation of Dicke-like states. In a recent publication in Phys. Rev. Lett., we show that these states contain at least 28-particle entanglement. We measure a generalized squeezing parameter of −11.4(5) dB, so far the best value in any atomic system.

With a novel criterion, we were able to estimate a lower bound for the so-called entanglement depth - the number of particles in the largest nonseparable subset. The measured entanglement depth of 28 proves that there must be at least one cluster of 28 atoms which are genuinely entangled with each other. The figure above illustrates an entanglement depth of 4 within a sample of 12 atoms.

Our work has been published in Phys. Rev. Lett. 112, 155304 (2014).

A short description can be found in Measuring Entanglement Among Many Particles,