Entanglement and spin squeezing in the two-atom Dicke model

Abstract

We analyze the relation between the entanglement and spin-squeezing parameter in the two-atom Dicke model and identify the source of the discrepancy recently reported by Banerjee and Zhou et al that one can observe entanglement without spin squeezing. Our calculations demonstrate that there are two criteria for entanglement, one associated with the two-photon coherences that create two-photon entangled states, and the other associated with populations of the collective states. We find that the spin-squeezing parameter correctly predicts entanglement in the two-atom Dicke system only if it is associated with two-photon entangled states, but fails to predict entanglement when it is associated with the entangled symmetric state. This explicitly identifies the source of the discrepancy and explains why the system can be entangled without spin-squeezing. We illustrate these findings in three examples of the interaction of the system with thermal, classical squeezed vacuum and quantum squeezed vacuum fields.

7 pages, 1 figure

References in corpus (6)

• Entanglement of Formation of an Arbitrary State of Two Qubits
• Separability Criterion for Density Matrices
• Entanglement of a Pair of Quantum Bits
• Separability criterion and inseparable mixed states with positive partial transposition
• Many-particle entanglement with Bose--Einstein condensates
• Entangled states and collective nonclassical effects in two-atom systems

Cited by in corpus (9)

• Quantum spin squeezing
• Entanglement in a second order quantum phase transition
• Entanglement dynamics in the Lipkin-Meshkov-Glick model
• Instability and entanglement of the ground state of the Dicke model
• Stationary two-atom entanglement induced by nonclassical two-photon correlations
• Spin squeezing as a measure of entanglement in a two qubit system
• Perspectives for a mixed two-qubit system with binomial quantum states
• Synthesis of maximally entangled mixed states and disentanglement in coupled Josephson charge qubits
• Quantitative aspects of entanglement in the optically driven quantum dots