Measurements with a noninvasive detector and dephasing mechanism

TL;DR

This paper investigates the measurement dynamics in quantum dot systems using a noninvasive detector, revealing how continuous observation affects quantum state decay and dephasing, with implications for quantum measurement theory.

Contribution

It provides a detailed description of the measurement process using Bloch equations and clarifies the effects of continuous observation on quantum state decay.

Findings

Measurement process described by Bloch-type equations.

Continuous observation can accelerate quantum state decay.

Dephasing width is uniquely defined during measurement.

Abstract

We study dynamics of the measurement process in quantum dot systems, where a particular state out of coherent superposition is observed. The ballistic point-contact placed near one of the dots is taken as a noninvasive detector. We demonstrate that the measurement process is fully described by the Bloch-type equations applied to the whole system. These equations clearly reproduce the collapse of the density-matrix into the statistical mixture in the course of the measurement process. The corresponding dephasing width is uniquely defined. We show that the continuous observation of one of the states in a coherent superposition may accelerate decay from this state -- in contradiction with rapidly repeated observations, which slow down the transitions between quantum states (the quantum Zeno effect).