# Measurement-induced strong Kerr nonlinearity for weak quantum states of light

## TL;DR

This paper demonstrates an experimental method to induce strong Kerr nonlinearity at the single photon level using measurement-induced quantum operations, enabling advanced optical quantum technologies.

## Contribution

It introduces a novel scheme combining photon addition and subtraction to achieve nonlinear phase shifts on weak quantum states of light.

## Key findings

- Successful implementation of measurement-induced Kerr nonlinearity
- Observation of sign change in off-diagonal density matrix elements
- Characterization of non-Gaussian output states

## Abstract

Strong nonlinearity at the single photon level represents a crucial enabling tool for optical quantum technologies. Here we report on experimental implementation of a strong Kerr nonlinearity by measurement-induced quantum operations on weak quantum states of light. Our scheme coherently combines two sequences of single photon addition and subtraction to induce a nonlinear phase shift at the single photon level. We probe the induced nonlinearity with weak coherent states and characterize the output non-Gaussian states with quantum state tomography. The strong nonlinearity is clearly witnessed as a change of sign of specific off-diagonal density matrix elements in Fock basis.