Thermal Electron Wavepacket Interferometry: Derivation and New Results

TL;DR

This paper introduces a formal equivalence linking thermal averages of quantum properties to time averages of a single wavepacket, revealing new insights into interference and temporal resolution in quantum conductance experiments.

Contribution

It establishes a novel formalism connecting thermal averages with wavepacket time averages, providing new physical interpretations and experimental implications for quantum conductance.

Findings

Thermal averages can be represented by a single wavepacket with thermal length.

Interference occurs when returning wavepackets arrive simultaneously.

Higher temperatures produce narrower wavepackets, enhancing temporal resolution.

Abstract

A novel formal equivalence between thermal averages of coherent properties (e.g. conductance), and time averages of a single wavepacket arises for Fermi gasses and certain geometries. In the case of one open channel in a quantum point contact (QPC), only one wavepacket history, with wavepacket width equal to thermal length, completely determines thermally averaged conductance. The formal equivalence moreover allows very simple physical interpretations of interference features surviving under thermal averaging. Simply put, pieces of thermal wavepacket returning to the QPC along independent paths must arrive at the same time in order to interfere. Remarkably, one immediate result of this approach is that higher temperature leads to narrower wavepackets and therefore better resolution of events in the time domain. In effect, experiments at 4.2 K are performing time gated experiments at better than a gigahertz. Experiments involving thermally averaged ballistic conductance in 2DEGS are presented as an application of this picture.