# Tomography of a Mode-Tunable Coherent Single-Photon Subtractor

## TL;DR

This paper introduces a mode-tunable coherent single-photon subtractor using sum frequency generation, enabling selective photon subtraction from specific time-frequency modes, which is crucial for advanced quantum information processing.

## Contribution

The work demonstrates the first experimental implementation of a mode-tunable coherent single-photon subtractor capable of targeting specific modes or superpositions, advancing quantum network capabilities.

## Key findings

- Successfully implemented mode-selective photon subtraction
- Characterized the process using quantum process tomography
- Enables non-Gaussian operations in quantum networks

## Abstract

Single-photon subtraction plays important roles in optical quantum information processing as it provides a non-Gaussian characteristic in continuous-variable quantum information. While the conventional way of implementing single-photon subtraction based on a low-reflectance beam splitter works properly for a single-mode quantum state, it is unsuitable for a multimode quantum state because a single photon is subtracted from all multiple modes without maintaining their mode coherence. Here we experimentally implement and characterize a mode-tunable coherent single-photon subtractor based on sum frequency generation. It can subtract a single photon exclusively from one desired time-frequency mode of light or from a coherent superposition of multiple time-frequency modes. To fully characterize the implemented single-photon subtractions, we employ quantum process tomography based on coherent states. The mode-tunable coherent single-photon subtractor will be an essential element for realizing non-Gaussian quantum networks necessary to get a quantum advantage in information processing.