Overview
This study explores the formation of polaritons through the hybridization of particle-hole excitations in an insulating phase with cavity photons. The focus is on processes occurring at sub-gap frequencies, where absorption is intrinsically suppressed. A central mechanism identified for driving hybridization strength is the Van Hove singularity (VHS) present in the joint density of states (JDOS) at the band gap. The research proposes that enhancing the singularity in the JDOS, specifically by implementing a high-order Van Hove singularity (HOVHS), can increase photon-interband transition hybridization.
Research Context
Polaritons are hybrid light-matter quasiparticles. In this context, they arise from the interaction between particle-hole excitations within an insulating material and cavity photons. A key challenge in generating strong polariton hybridization is to achieve it without incurring significant absorption, particularly for applications in quantum-nonlinear optics. The strength of this hybridization is directly linked to the Van Hove singularity present in the joint density of states at the band gap. A stronger singularity in the JDOS leads to greater hybridization between the photon and the interband transitions.
Approach
The proposed approach centers on engineering the material's band structure to modify the Van Hove singularity in the JDOS. Specifically, the researchers suggest engineering a non-parabolic momentum dispersion of the energy bands in the vicinity of the band gap. This modification is intended to create a high-order Van Hove singularity. The aim of this HOVHS is to increase the singularity's strength and, consequently, enhance polariton hybridization without introducing absorption.
Ultracold atoms confined in tunable optical lattices are identified as a suitable platform for implementing this concept. Such systems offer the flexibility to engineer two-dimensional gapped phases with specific, non-trivial band dispersions at the gap edge. An additional advantage of using polarized fermionic ultracold atoms is their non-interacting nature, which inherently prevents the formation of sub-gap excitations. In solid-state systems, these sub-gap excitations are common and could otherwise compromise the desired absence of absorption below the gap, thereby potentially spoiling the utility of the engineered HOVHS.
Findings
- The strength of polariton hybridization between a photon and interband transitions is directly influenced by the Van Hove singularity in the joint density of states at the band gap.
- A stronger singularity in the JDOS at the band gap leads to increased hybridization between the photon and the interband transitions.
- Engineering a non-parabolic momentum dispersion of bands around the gap can lead to the implementation of a high-order Van Hove singularity (HOVHS) in the JDOS.
- The implementation of an HOVHS in the JDOS is proposed as a mechanism to increase the singularity and thereby enhance polariton hybridization without absorption.
- Ultracold atoms in tunable optical lattices are an ideal platform for realizing two-dimensional gapped phases with non-trivial band dispersions at the gap due to their tunability.
- Polarized fermionic atoms, owing to their intrinsic non-interacting nature, prevent the emergence of sub-gap excitations that could otherwise hinder the absence of absorption below the gap.
Why This Matters
The findings indicate that band-engineering at the gap edge represents a promising method for controlling polariton properties. Such control could have direct applications within the field of quantum-nonlinear optics.