Stub model for dephasing in a quantum dot

TL;DR

This paper introduces a dephasing stub model as an alternative to the dephasing lead model for simulating decoherence in quantum dots, emphasizing its advantages in maintaining a closed system for individual measurements.

Contribution

The paper proposes and analyzes a dephasing stub model, highlighting its differences from the dephasing lead model and its suitability for quantum algorithms based on individual measurement outcomes.

Findings

Dephasing stub can suppress quantum interference effectively.

The model maintains a closed system with zero current at each measurement.

Parameter range identified where classical noise is negligible.

Abstract

As an alternative to Buttiker's dephasing lead model, we examine a dephasing stub. Both models are phenomenological ways to introduce decoherence in chaotic scattering by a quantum dot. The difference is that the dephasing lead opens up the quantum dot by connecting it to an electron reservoir, while the dephasing stub is closed at one end. Voltage fluctuations in the stub take over the dephasing role from the reservoir. Because the quantum dot with dephasing lead is an open system, only expectation values of the current can be forced to vanish at low frequencies, while the outcome of an individual measurement is not so constrained. The quantum dot with dephasing stub, in contrast, remains a closed system with a vanishing low-frequency current at each and every measurement. This difference is a crucial one in the context of quantum algorithms, which are based on the outcome of individual measurements rather than on expectation values. We demonstrate that the dephasing stub model has a parameter range in which the voltage fluctuations are sufficiently strong to suppress quantum interference effects, while still being sufficiently weak that classical current fluctuations can be neglected relative to the nonequilibrium shot noise.