Single-photon exchange interaction in a semiconductor microcavity

TL;DR

This paper demonstrates that a single polariton in a semiconductor microcavity can induce a significant indirect exchange interaction between localized spins, with the interaction's strength depending on coupling parameters and detuning.

Contribution

It provides an exact quantum mechanical analysis showing how a single polariton mediates exchange interactions between spins in a quantum dot-microcavity system, revealing temperature-dependent effects.

Findings

Single polariton induces sizable exchange interaction between spins.

Interaction strength depends on dot-cavity coupling and detuning.

Ferromagnetic Mn-Mn coupling persists above 1 K, exciton-mediated at 15 K.

Abstract

We consider the effective coupling of localized spins in a semiconductor quantum dot embedded in a microcavity. The lowest cavity mode and the quantum dot exciton are coupled and close in energy, forming a polariton. The fermions forming the exciton interact with localized spins via exchange. Exact diagonalization of a Hamiltonian in which photons, spins and excitons are treated quantum mechanically shows that {\it a single polariton} induces a sizable indirect exchange interaction between otherwise independent spins. The origin, symmetry properties and the intensity of that interaction depend both on the dot-cavity coupling and detuning. In the case of a (Cd,Mn)Te quantum dot, Mn-Mn ferromagnetic coupling mediated by a single photon survives above 1 K whereas the exciton mediated coupling survives at 15 K.