# State of a particle pair produced by the Schwinger effect is not necessarily a maximally entangled Bell state

## TL;DR

This paper investigates how the spin entanglement of particle pairs produced by the Schwinger effect depends on their momenta and external field angular momentum, revealing conditions for maximal entanglement.

## Contribution

It demonstrates that the spin state is not always maximally entangled, especially when particles have transverse momentum, due to angular momentum transfer from the external field.

## Key findings

- Maximal entanglement occurs only when particle momenta are parallel to the electric field.
- Transverse momentum results in less than maximal spin entanglement.
- External field angular momentum influences the spin state of produced pairs.

## Abstract

We analyze the spins of a Schwinger particle pair in a spatially uniform but time dependent electric field. The particle pair's spins are in the maximally entangled Bell state only if the particles' momenta are parallel to the electric field. However if transverse momentum is present, the spins are not in the maximally entangled Bell state. The reason is that the pair is created by the external field, which also carries angular momentum, and the particle pair can take away some of this external angular momentum.