Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation

TL;DR

This paper investigates the nonlinear current response of a many-level tunneling system under high-frequency fields, revealing sharp harmonic generation due to multi-photon processes, with potential experimental implications.

Contribution

It provides an exact calculation of the nonlinear tunneling current and demonstrates frequency multiplication effects in a many-level system using nonequilibrium Green functions.

Findings

Fourier components of current peak at specific harmonics

Frequency multiplication arises from multi-photon absorption/emission

Potential for experimental observation of nonlinear harmonic generation

Abstract

The fully nonlinear response of a many-level tunneling system to a strong alternating field of high frequency $\omega$ is studied in terms of the Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent tunneling current $I(t)$ is calculated exactly and its resonance structure is elucidated. In particular, it is shown that under certain reasonable conditions on the physical parameters, the Fourier component $I_{n}$ is sharply peaked at $n=\frac {\Delta E} {\hbar \omega}$, where $\Delta E$ is the spacing between two levels. This frequency multiplication results from the highly nonlinear process of $n$ photon absorption (or emission) by the tunneling system. It is also conjectured that this effect (which so far is studied mainly in the context of nonlinear optics) might be experimentally feasible.