Ultrastrong coupling between a cavity resonator and the cyclotron transition of a 2D electron gas in the case of integer filling factor

TL;DR

This paper theoretically explores the ultrastrong coupling between a cavity resonator and cyclotron transitions in a 2D electron gas at integer filling factors, revealing potential for coupling strengths much greater than unity.

Contribution

The study derives an effective quantum Hamiltonian for magnetopolariton excitations and analyzes the scaling of vacuum Rabi frequency in high-mobility 2D electron gases.

Findings

Vacuum Rabi frequency scales as √(α n_QW ν)

Ultrastrong coupling (Ω₀/ω₀ > 1) achievable at high filling factors

Implications for microwave-range cyclotron transitions

Abstract

We investigate theoretically the coupling between a cavity resonator and the cyclotron transition of a two dimensional electron gas under an applied perpendicular magnetic field. We derive and diagonalize an effective quantum Hamiltonian describing the magnetopolariton excitations of the two dimensional electron gas for the case of integer filling factors. The limits of validity of the present approach are critically discussed. The dimensionless vacuum Rabi frequency $\Omega_0/\omega_0$ (i.e., normalized to the cyclotron frequency $\omega_0$) is shown to scale as $\sqrt{\alpha\: n_{QW} \nu}$, where $\alpha$ is the fine structure constant, $n_{QW}$ is the number of quantum wells and $\nu$ is the filling factor in each well. We show that with realistic parameters of a high-mobility semiconductor two dimensional electron gas, the dimensionless coupling $\Omega_0/\omega_0$ can be much larger than 1 in the case of $\nu \gg 1$, the latter condition being typically realized for cyclotron transitions in the microwave range. Implications of such ultrastrong coupling regime are discussed.