# Classicalization of Quantum State of Detector by Amplification Process

## TL;DR

This paper investigates how phase-preserving linear amplification of a detector's pointer can produce a classical state from a quantum superposition, clarifying the quantum-to-classical transition in measurement devices.

## Contribution

It demonstrates that amplification can effectively produce classical states of a detector's pointer, preventing the formation of quantum superpositions after measurement.

## Key findings

- Amplification leads to classical states of the detector pointer.
- The process prevents the pointer from being projected into quantum superpositions.
- Quantitative analysis confirms the classicalization effect.

## Abstract

It has been shown that a macroscopic system being in a high-temperature thermal coherent state can be, in principle, driven into a non-classical state by coupling to a microscopic system. Therefore, thermal coherent states do not truly represent the classical limit of quantum description. Here, we study the classical limit of quantum state of a more relevant macroscopic system, namely the pointer of a detector, after the phase-preserving linear amplification process. In particular, we examine to what extent it is possible to find the corresponding amplified state in a superposition state, by coupling the pointer to a qubit system. We demonstrate quantitatively that the amplification process is able to produce the classical limit of quantum state of the pointer, offering a route for a classical state in a sense of not to be projected into a quantum superposition state.