A Demonstration of Quantum Key Distribution with Entangled Photons for the Undergraduate Laboratory

TL;DR

This paper presents an undergraduate laboratory experiment demonstrating quantum key distribution using entangled photons, illustrating quantum principles like superposition and measurement for secure communication and eavesdropper detection.

Contribution

It introduces a practical, tabletop experiment for students to learn quantum key distribution with entangled photons, including eavesdropper simulation and analysis.

Findings

Quantum key distribution ensures communication secrecy.

Eavesdropper measurement disrupts quantum states.

The experiment effectively demonstrates quantum security principles.

Abstract

Now that fundamental quantum principles of indeterminacy and measurement have become the basis of new technologies that provide secrecy between two communicating parties, there is a need to provide teaching laboratories that illustrate how these technologies work. In this article we describe a laboratory exercise in which students perform quantum key distribution with single photons, and see how the secrecy of the communication is ensured by the principles of quantum superposition and state projection. We used a table-top apparatus, similar to those used in correlated-photon undergraduate laboratories, to implement the Bennett-Brassard-84 protocol with polarization-entangled photons. Our experiment shows how the communication between two parties is disrupted by an eavesdropper. We use a simple quartz plate to mimic how an eavesdropper intercepts, measures, and resends the photons used in the communication, and we analyze the state of the light to show how the eavesdropper changes it.