# Robust mode conversion in NV centers using exceptional points

## TL;DR

This paper demonstrates how NV centers can be used as topological mode switches by exploiting exceptional points, enabling non-reciprocal mode switching in open quantum systems at room temperature.

## Contribution

It extends topological mode switching theory from pure to mixed states, showing practical implementation in NV centers with potential quantum information applications.

## Key findings

- Successful simulation of topological and non-reciprocal mode switching
- Quantum correlations decrease significantly at room temperature
- Framework applicable to open quantum systems with mixed states

## Abstract

We show that microwave-driven NV centers can function as topological mode switches by utilizing a special degeneracy called an exceptional point (EP). By tuning the intensities and frequencies of the driving fields, we find an EP---where two normal modes of the system coalesce---and, then, use it to simulate the dynamics and demonstrate topological and non-reciprocal mode switching. By comparing density matrices of the input and output states, we find that the quantum correlations decrease by three orders of magnitude at room temperature, and discuss ways for improving this result. This work extends the theory of topological mode switches (originally derived for pure states) to mixed states and is, therefore, applicable to general open quantum systems. Our theory enables exploring new phenomena (e.g., high-order EPs in low-dimensional systems) and presents a crucial step towards incorporating topological mode switches in quantum-information applications.