# Scalable on-chip quantum state tomography

## TL;DR

This paper introduces a scalable quantum state tomography method that significantly reduces measurement complexity, demonstrated on a photonic chip with high fidelity for two- and three-photon states.

## Contribution

The paper presents a novel measurement technique that scales linearly with qubit number, enabling efficient characterization of large quantum systems.

## Key findings

- Measurement complexity scales linearly with qubits
- Achieved 99.67% fidelity in state reconstruction
- Demonstrated on integrated photonic chip for 2- and 3-photon states

## Abstract

Quantum information systems are on a path to vastly exceed the complexity of any classical device. The number of entangled qubits in quantum devices is rapidly increasing and the information required to fully describe these systems scales exponentially with qubit number. This scaling is the key benefit of quantum systems, however it also presents a severe challenge. To characterize such systems typically requires an exponentially long sequence of different measurements, becoming highly resource demanding for large numbers of qubits. Here we propose a novel and scalable method to characterize quantum systems, where the complexity of the measurement process only scales linearly with the number of qubits. We experimentally demonstrate an integrated photonic chip capable of measuring two- and three-photon quantum states with reconstruction fidelity of 99.67%.