Quantum noise of white light cavity using double-pumped gain medium

TL;DR

This paper evaluates the quantum noise in a white-light cavity using a double-pumped gain medium, revealing stability constraints that prevent sensitivity enhancement, thus guiding future research directions.

Contribution

It provides a detailed quantum noise analysis of the white-light cavity with a double-pumped gain medium, highlighting stability issues that limit sensitivity improvements.

Findings

Additional noise from parametric amplification is present.

System stability constraints prevent net sensitivity enhancement.

No improvement in shot-noise limited sensitivity was found.

Abstract

Laser interferometric gravitational-wave detectors implement Fabry-Perot cavities to increase their peak sensitivity. However, this is at cost of reducing their detection bandwidth, which origins from the propagation phase delay of the light. The "white-light-cavity" idea, first proposed by Wicht et al. [Optics Communications 134, 431 (1997)], is to circumvent this limitation by introducing anomalous dispersion, using double-pumped gain medium, to compensate for such phase delay. In this article, starting from the Hamiltonian of atom-light interaction, we apply the input-output formalism to evaluate the quantum noise of the system. We find that apart from the additional noise associated with the parametric amplification process noticed by others, the stability condition for the entire system poses an additional constraint. Through surveying the parameter regimes where the gain medium remains stable (not lasing) and stationary, we find that there is no net enhancement of the shot-noise limited sensitivity. Therefore, other gain mediums or different parameter regimes shall be explored for realizing the white light cavity.