An Inexpensive Optical Quantum-Key-Distribution Demo with Swiveled Cellophane Waveplates

There is much interest in introducing quantum physics to general and young audiences, particularly non-physics college and K-12 student populations. Hands-on laboratory demonstrations or simulations are powerful tools in facilitating a deep understanding of abstract quantum principles, such as superposition and measurement, and their applications. Quantum key distribution (QKD) has emerged as an important technology that uses these quantum principles. In this contribution, I present a simple and inexpensive demonstration of a QKD protocol using light’s polarization. It uses an inexpensive diode laser and optical components. I show how to diagnose and use cellophane wrappers as polarization waveplates. A key aspect involves using the optical components, such that once set up they only swivel about their holders to switch between the choices in the demo: binary data (0 or 1); and sender, receiver, and eavesdropper measurement bases. The detection consists of a clear natural calcite crystal to vividly display the outcomes on a screen.