Quantum Theory of All-Optical Switching in Nonlinear Sagnac Interferometers

TL;DR

This paper develops a comprehensive quantum theory for all-optical switches based on nonlinear Sagnac interferometers, accurately modeling quantum noise and aligning well with experimental results, thus aiding future quantum network device design.

Contribution

It introduces a detailed quantum theoretical framework for nonlinear Sagnac interferometer switches, including quantum noise modeling, validated by experimental data.

Findings

Good agreement between theory and experiment without fitting parameters

Quantum noise is effectively modeled in the switch dynamics

Guides future design of quantum optical switches for networking

Abstract

Recently, our group has demonstrated an ultrafast, low-loss, fiber-loop switch based on a nonlinear Sagnac-interferometer design, using which entangled photons were shown to be routed without any measurable degradation in their entanglement fidelity [Hall {\it et al.}, Phys. Rev. Lett. {\bf 106}, 053901 (2011)]. Such a device represents an enabling technology for a rich variety of networked quantum applications. In this paper we develop a comprehensive quantum theory for such switches in general, i.e., those based on nonlinear Sagnac interferometers, where the in-coupling of quantum noise is carefully modeled. Applying to the fiber-loop switch, the theory shows good agreement with the experimental results without using any fitting parameter. This theory can serve as an important guiding tool for configuring switches of this kind for future quantum networking applications.