Nonclassical detectors and nonclassicality

TL;DR

This paper demonstrates that nonclassical effects in quantum measurements depend critically on the nonclassical nature of the measurement apparatus, challenging the common attribution solely to the quantum state.

Contribution

It reveals that nonclassical phenomena require nonclassical measurement devices, providing a new perspective on the origin of quantum nonclassicality.

Findings

Nonclassical effects only appear with nonclassical measurements.

Classical models can explain observed statistics with classical measurements.

Measurement nonclassicality is essential for observing quantum nonclassicality.

Abstract

According to Born's rule quantum probabilities are given by the overlap between the system state and measurement states in a quite symmetrical way. This means that both contribute to any observed nonclassical effect that is usually attributed just to the observed light state. This is relevant since typical measurement are highly nonclassical by themselves, such as number states and quadrature eigenstates. We show that nonclassical effects only arise provided that the measurement is itself nonclassical. Otherwise there is a classical-like model accounting for the observed statistics.