# Nonclassical primordial gravitational waves from the initial entangled state

## TL;DR

This paper investigates the nonclassical nature of primordial gravitational waves, showing that initial entangled states like alpha-vacua can produce sub-Poissonian graviton statistics without phase constraints, unlike the Bunch-Davies vacuum.

## Contribution

It extends the analysis of primordial gravitational waves to initial entangled states, revealing new conditions for nonclassicality in the early universe.

## Key findings

- Initial entangled states lead to sub-Poissonian graviton statistics.
- Sub-Poissonian behavior occurs without phase constraints in entangled states.
- Differences between Bunch-Davies vacuum and alpha-vacua in gravitational wave statistics.

## Abstract

The nonclassicality of primordial gravitational waves (PGWs) is characterized in terms of sub-Poissonian graviton statistics. The sub-Poissonian statistics are realized when quantum states are squeezed coherent states. In the presence of matter fields, the Universe experiences the squeezed coherent state during inflation. The condition to realize the sub-Poissonian graviton statistics is translated into the frequency range of gravitational waves. If the initial state is the Bunch-Davies vacuum, there is another necessary condition between phases of squeezing and coherent parameters. Here, we extend the initial state to entangled states. We consider $\alpha$-vacua as the initial entangled state that are more general de Sitter invariant vacua than the Bunch-Davies vacuum. We find that, unlike the Bunch-Davies vacuum, PGWs generated in the initial entangled state become sub-Poissonian without requiring the condition between the phases.