# Delay and polarization routing of single photons

## TL;DR

This paper demonstrates controllable delay and routing of single photons from a quantum dot using atomic vapor, enabling polarization and magnetic field-dependent manipulation for quantum communication.

## Contribution

It introduces a method to actively control photon delay and routing via atomic vapor, tunable by polarization and magnetic fields, advancing quantum photonic device capabilities.

## Key findings

- Achieved a 25 ns delay with tunability over 600 ps.
- Demonstrated polarization-dependent routing of photons.
- Validated the experimental results with a comprehensive theoretical model.

## Abstract

The full control of single photons is important in quantum information and quantum networking. A convenient storage device for photons is the key to memory assisted quantum communication and computing. While even a simple optical fiber can act as a convenient and reliable storage device, its storage time is tightly fixed and cannot be adapted. Therefore, the photon storage should ideally be actively controllable by external means, such as magnetic or electric control fields. In order to multiplex several photons, an active routing would also be desirable. Here we show that single photons of a semiconductor quantum dot can be deliberately delayed by an atomic vapor. Also, the output path can be selected, depending on an external magnetic field. By selecting the input polarization of the photons and by aligning the external magnetic field of the hot atomic vapor, the delay-based storage can be fine tuned to a deliberate value. With an overall delay of 25 ns, we are able to fine tune by more than 600 ps. Depending on the input polarization, the photons are routed into different output ports. The experimental data is fully resembled by a theoretical model, which describes the group velocity delay under consideration of spectral diffusion and considers the complex refractive index of the atomic vapor. The present results enable the use of an atomic vapor as a wavelength selective delay and allows for routing the single photons according to their polarization and an external magnetic field.