Two-axis two-spin squeezed states

TL;DR

This paper investigates the properties and entanglement features of two-axis two-spin squeezed states, revealing their potential for Bell inequality violation and their behavior over different timescales.

Contribution

It introduces a detailed analysis of two-spin squeezed states, including their generation, properties, and entanglement, extending understanding of spin-based quantum states.

Findings

States approximate two-mode squeezed vacuum at short times

Bell state entanglement is produced for qubits

Bell inequality can be violated with these states

Abstract

The states generated by the two-spin generalization of the two-axis countertwisting Hamiltonian are examined. We analyze the behavior at both short and long timescales, by calculating various quantities such as squeezing, spin expectation values, probability distributions, entanglement, Wigner functions, and Bell correlations. In the limit of large spin ensembles and short interaction times, the state can be described by a two-mode squeezed vacuum state; for qubits, Bell state entanglement is produced. We find that the Hamiltonian approximately produces two types of spin-EPR states, and the time evolution produces aperiodic oscillations between them. In a similar way to the basis invariance of Bell states and two-mode squeezed vacuum states, the Fock state correlations of spin-EPR states are basis invariant. We find that it is possible to violate a Bell inequality with such states, although the violation diminishes with increasing ensemble size. Effective methods to detect entanglement are also proposed, and formulas for the optimal times to enhance various properties are calculated.