Demonstrating macroscopic entanglement based on Kerr non-linearities requires extreme phase resolution

TL;DR

This paper explores the challenge of observing macroscopic quantum effects using Kerr non-linearities, emphasizing that extreme phase control is essential for creating entangled states and verifying quantum phenomena at large scales.

Contribution

It demonstrates that achieving macroscopic entanglement with Kerr non-linearities requires extremely precise phase control, highlighting a fundamental difficulty in observing quantum effects macroscopically.

Findings

Creating entangled coherent states demands precise phase control.

Measurement of quantum effects at macroscopic scales is limited by phase precision.

Macroscopic quantum effects are inherently difficult to observe without extreme control.

Abstract

Entangled coherent states, which can in principle be created using strong Kerr non-linearities, allow the violation of Bell inequalities for very coarse-grained measurements. This seems to contradict a recent conjecture that observing quantum effects in macroscopic systems generally requires very precise measurements. However, here we show that both the creation of the required states and the required measurements rely on being able to control the phase of the necessary Kerr-nonlinearity based unitary operations with extreme precision. This lends support to the idea that there is a general principle that makes macroscopic quantum effects difficult to observe, even in the absence of decoherence.