Spin squeezing under decoherence: Role of the quantum phase transition
Zhe Sun · Physical Review A · 2011
In order to witness multipartite correlations beyond pairwise entanglement, we study the spin-squeezing evolution of a spin-1/2 ensemble in environments with quantum phase transitions. Each spin half of the ensemble evolves under its own decoherence channel, which is modeled by a central spin 1/2 surrounded by a spin-1/2 $XY$ chain. We employ four spin-squeezing parameters to describe squeezing, and their expressions at time $t$ are analytically calculated for the spin ensemble in a collective initial state. It is found that spin squeezing of an auxiliary ensemble signals very well the critical regions of the environment. Quantum fluctuations of the environment accelerate the decay of spin squeezing and dramatically change spin squeezing.