Quadrature coherence scale driven fast decoherence of bosonic quantum field states

TL;DR

This paper introduces the quadrature coherence scale (QCS) as a measure of coherence in bosonic quantum states, showing its relation to decoherence, classicality, and nonclassicality, with implications for understanding quantum-to-classical transition.

Contribution

The paper defines the QCS, analyzes its role in decoherence under thermal baths, and links it to optical classicality and nonclassicality, providing new insights into quantum state fragility.

Findings

Large QCS states decohere faster

High QCS states are harder to measure

Large QCS indicates strong optical nonclassicality

Abstract

We introduce, for each state of a bosonic quantum field, its quadrature coherence scale (QCS), a measure of the range of its quadrature coherences. Under coupling to a thermal bath, the purity and QCS are shown to decrease on a time scale inversely proportional to the QCS squared. The states most fragile to decoherence are therefore those with quadrature coherences far from the diagonal. We further show a large QCS is difficult to measure since it induces small scale variations in the state's Wigner function. These two observations imply a large QCS constitutes a mark of "macroscopic coherence". Finally, we link the QCS to optical classicality: optical classical states have a small QCS and a large QCS implies strong optical nonclassicality.