Decoherence of the Kondo Singlet via a Quantum Point Contact Detector

TL;DR

This paper studies how charge detection via a quantum point contact causes decoherence of the Kondo singlet in a quantum dot, explaining experimental anomalies and analyzing shot noise correlations.

Contribution

It introduces a combined variational and density matrix approach to quantify decoherence effects caused by QPC detection on the Kondo singlet.

Findings

Decoherence destroys the Kondo singlet through phase and magnitude-sensitive detection.

Phase-sensitive detection explains anomalous experimental features.

Shot noise correlations relate to decoherence in the quantum dot.

Abstract

We investigate the effect of the charge state measurement of the Kondo singlet for a quantum dot transistor via a capacitively coupled quantum point contact detector. By employing the variational ansatz for the singlet ground state of the quantum dot combined with the density matrix formulation for the coupled system, we show that the coherent Kondo singlet is destroyed by the phase-sensitive as well as the magnitude-sensitive detection in the transmission/reflection coefficients at the quantum point contact. We argue that the phase-sensitive component of the decoherence rate may explain the anomalous features observed in a recent experiment by Avinun-Kalish {\em et al.} (Phys. Rev. Lett. {\bf 92}, 156801 (2004)). We also discuss the correlations of the shot noise at the quantum point contact detector and the decoherence in the quantum dot.