# Spin anisotropic interactions of lower-polaritons in the vicinity of polaritonic Feshbach resonance

## TL;DR

This study experimentally measures the spin-dependent interactions of lower-polaritons near a Feshbach resonance, revealing enhanced attraction and dissipation due to biexciton coupling, supported by theoretical analysis.

## Contribution

It provides the first experimental determination of spinor interaction constants of lower-polaritons near a polaritonic Feshbach resonance, combining spectroscopy with theoretical modeling.

## Key findings

- Enhanced attractive interaction near biexciton resonance
- Increased dissipative nonlinearity for anti-parallel spins
- Evidence of a scattering resonance between lower-polaritons and biexcitons

## Abstract

We determine experimentally the spinor interaction constants of lower-polaritons $\alpha_1$ and $\alpha_2$ using resonant pump-probe spectroscopy with a spectrally narrow pump pulse. Our experimental findings are analyzed with the Bogoliubov-like theory and mean-field two channel model based on the lower-polariton and biexciton basis. We find an enhancement of the attractive interaction and dissipative nonlinearity of lower-polaritons with anti-parallel spins in the vicinity of the biexciton resonance when the energy of two lower-polaritons approaches energetically that of the biexciton. These observations are consistent with the existence of a scattering resonance between lower-polaritons and biexcitons (polaritonic Feshbach resonance).