Global versus local quantum squeezing in composite systems

We investigate relations between the global squeezing of composite systems and the local squeezing of subsystems. For the pure symmetric product states, the global squeezing parameter is found to be equal to the local one for both spin and bosonic systems. Hence, a pure symmetric state is entangled if the global parameter is not equal to the local one. Two origins of the global squeezing are identified: one is from the local squeezing and the other from quantum correlations. For both spin and bosonic systems, we find that the entanglement can lead to a smaller global squeezing parameter; namely, the global squeezing is enhanced.