A simplified single-photon quantum key distribution setup for a quantum teaching laboratory

One of the clearest applications of quantum information science occurs in cryptography, where the fundamental principles of quantum physics can be harnessed to encrypt messages in a way that is secure and can unambiguously reveal the presence of an eavesdropper. Here we present a simplified experimental setup that demonstrates the core concepts of quantum key distribution while using minimal resources and maintaining a small footprint. The experimental design is compatible with both a multi- and single-photon implementation, and it also can demonstrate the presence of an eavesdropper that is detectable in the communication error rate. We will discuss the successful implementation of this setup at the University of Chicago, in a quantum teaching laboratory course targeted at the undergraduate level.