Revealing strong correlations in higher order transport statistics: a noncrossing approximation approach

TL;DR

This paper introduces a computationally efficient method based on the propagator noncrossing approximation to analyze higher order transport statistics in quantum systems, revealing the significant impact of correlations like Kondo effects.

Contribution

The paper develops and validates a noncrossing approximation method for calculating full counting statistics, capturing correlation effects beyond traditional quantum master equations.

Findings

NCA accurately computes higher order cumulants in quantum transport.

Correlation effects significantly influence transport distributions.

Higher order cumulants serve as indicators of Kondo correlations.

Abstract

We present a method for calculating the full counting statistics of a nonequilibrium quantum system based on the propagator noncrossing approximation (NCA). This numerically inexpensive method can provide higher order cumulants for extended parameter regimes, rendering it attractive for a wide variety of purposes. We compare NCA results to Born-Markov quantum master equations (QME) results to show that they can access different physics, and to numerically exact inchworm quantum Monte-Carlo data to assess their validity. As a demonstration of its power, the NCA method is employed to study the impact of correlations on higher order cumulants in the nonequilibrium Anderson impurity model. The four lowest order cumulants are examined, allowing us to establish that correlation effects have a profound influence on the underlying transport distributions. Higher order cumulants are therefore demonstrated to be a proxy for the presence of Kondo correlations in a way that cannot be captured by simple QME methods.