# Stimulated emission of relic gravitons and their super-Poissonian statistics

## TL;DR

This paper investigates the quantum statistical properties of relic gravitons, showing that their second-order coherence remains super-Poissonian regardless of initial states, with implications for their quantum origin detection.

## Contribution

It demonstrates that relic gravitons' super-Poissonian statistics persist across various initial quantum states, providing insights into their quantum nature and emission processes.

## Key findings

- Relic gravitons exhibit super-Poissonian second-order coherence.
- Initial state properties influence but do not eliminate super-Poissonian statistics.
- Quantum origin can be inferred from Hanbury Brown-Twiss correlations.

## Abstract

The degree of second-order coherence of the relic gravitons produced from the vacuum is super-Poissonian and larger than in the case of a chaotic source characterized by a Bose-Einstein distribution. If the initial state does not minimize the tensor Hamiltonian and has a dispersion smaller than its averaged multiplicity, the overall statistics is by definition sub-Poissonian. Depending on the nature of the sub-Poissonian initial state, the final degree of second-order coherence of the quanta produced by stimulated emission may diminish (possibly even below the characteristic value of a chaotic source) but it always remains larger than one (i.e. super-Poissonian). When the initial statistics is Poissonian (like in the case of a coherent state or for a mixed state weighted by a Poisson distribution) the degree of second-order coherence of the produced gravitons is still super-Poissonian. Even though the quantum origin of the relic gravitons inside the Hubble radius can be effectively disambiguated by looking at the corresponding Hanbury Brown-Twiss correlations, the final distributions caused by different initial states maintain their super-Poissonian character which cannot be altered.