# Emission Noise and High Frequency Cut-Off of the Kondo Effect in a Quantum Dot

## TL;DR

This study measures the emission noise of a carbon nanotube quantum dot in the Kondo regime, revealing a high frequency cut-off related to the Kondo temperature and coupling asymmetry, influenced by voltage-induced spin relaxation.

## Contribution

It provides the first experimental observation of a high frequency cut-off in Kondo emission noise and links it to coupling asymmetry and non-equilibrium effects.

## Key findings

- High frequency cut-off of emission noise is of the order of a few times the Kondo temperature.
- Asymmetry in contact coupling shifts the cut-off frequency.
- Voltage-induced spin relaxation explains the low frequency cut-off in symmetric coupling.

## Abstract

By coupling on chip a carbon nanotube to a quantum noise detector, a superconductor-insulator-superconductor junction, via a resonant circuit, we measure the emission noise of a carbon nanotube quantum dot in the Kondo regime. The signature of the Kondo effect in the current noise is measured for different ratios of the Kondo temperature over the measured frequency and for different asymmetries of the coupling to the contacts, and compared to finite frequency quantum noise calculations. Our results point towards the existence of a high frequency cut-off of the electronic emission noise associated with the Kondo resonance. This cut-off frequency is of the order of a few times the Kondo temperature when the electronic system is close to equilibrium, which is the case for a strongly asymmetric coupling. On the other hand, this cut-off is shifted to lower frequency in a symmetric coupling situation, where the bias voltage drives the Kondo state out-of-equilibrium. We then attribute the low frequency cut-off to voltage induced spin relaxation.