# Effect of unbalanced and common losses in quantum photonic integrated circuits

## TL;DR

This paper analyzes how unbalanced and shared losses in quantum photonic integrated circuits degrade the performance of quantum gates, emphasizing the importance of loss management for scalable quantum information processing.

## Contribution

It provides a detailed analysis of how different types of loss affect integrated linear optical quantum gates, highlighting the impact on eigenmode orthogonality and gate fidelity.

## Key findings

- Loss destroys eigenmode orthogonality and phase relations.
- Shared loss reduces fidelity of quantum operations.
- Fidelity drops significantly when loss approaches coupling strength.

## Abstract

Loss is inevitable for the optical system due to absorption of materials, scattering caused by the defects and surface roughness. In quantum optical circuits, the loss can not only reduce the intensity of signal, but also affect the performance of quantum operations. In this work, we divide losses into unbalanced linear loss and shared common loss, and provide a detailed analysis on how loss affects the integrated linear optical quantum gates. It is found that the orthogonality of eigenmodes and the unitary phase relation of the coupled waveguide modes are destroyed by the loss. As a result, the fidelity of single- and two-qubit operations decrease significant as the shared loss becomes comparable to the coupling strength. Our results are important for the investigation of large-scale photonic integrated quantum information process.

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Source: https://tomesphere.com/paper/1705.10472