Two-path interference of single-particle pulses measured by the Unruh-DeWitt-type quantum detector

TL;DR

This paper investigates how a quantum detector modeled after the Unruh-DeWitt detector can observe two-path interference of single-particle pulses, revealing differences from classical detection and illustrating decoherence effects.

Contribution

It introduces a quantum detector model that maintains interference patterns over long path differences and compares its behavior to classical detectors, advancing understanding of quantum measurement.

Findings

Quantum detectors can observe interference beyond coherence length.

Ensemble of quantum detectors behaves classically when coherence is short.

The model clarifies the role of decoherence in quantum-to-classical transition.

Abstract

We study the two-path interference of single-particle pulses measured by the Unruh-DeWitt-type quantum detector, which itself is a quantum state as well as the incoming pulse, and of which the interaction with the pulse is described by unitary quantum evolution instead of a nonunitary collapsing process. Provided that the quantum detector remains coherent in time long enough, the detection probability still manifests the two-path interference pattern even if the length difference between the two paths considerably exceeds the coherence length of the single-particle pulse, contrary to the result measured by an ordinary classical detector. Furthermore, it is formally shown that an ensemble of identical Unruh-DeWitt-type quantum detectors collectively behaves as an ordinary classical detector, if coherence in time of each individual quantum detector becomes sufficiently short. Our study provides a concrete yet manageable theoretical model to investigate the two-path interference measured by a quantum detector and facilitates a quantitative analysis of the difference between classical and quantum detectors. The analysis affirms the main idea of decoherence theory: quantum behavior is lost as a result of quantum decoherence.