# Entangling and squeezing atoms by weak measurement

## TL;DR

This paper introduces a weak measurement technique to entangle and squeeze atoms, achieving significant squeezing even with minimal light-atom coupling, and enabling transformation into different squeezing types.

## Contribution

It presents a novel weak measurement method for atomic entanglement and squeezing, surpassing traditional limits and allowing control over squeezing types.

## Key findings

- Achieves large atomic squeezing with weak light-atom coupling.
- Post-selection enhances entanglement and squeezing.
- Transforms squeezing into one-axis or two-axis twisting types.

## Abstract

A weak measurement approach is proposed to entangle and squeeze atoms. We show that even for very small coupling strength between light and atoms, one can achieve large squeezing unattainable with normal measurement-based squeezing. Post-selecting the photons interacting with spins via a weak off-resonant quantum nondemolition interaction (QND) in a state nearly orthogonal to its initial state can strengthen the entanglement among elementary spins and thus enhance spin squeezing. The squeezing process is probabilistic but the created state is unconditionally determined. Further control of the post-selection parameter and the detection process can transform the QND-like spin squeezing into the one-axis-twisting or even two-axis-twisting type.