I recently was watching these 2 videos on Coursera which show how to build a simple quantum computer that can implement the simplest case of the Deutsch-Jozsa algorithm (which uses only 2 qubits).
In it, the professor mentioned that the photon represented 2 qubits: one was the polarization qubit and one was the path/position qubit. Later, the professor stated that a half-wave plate affected the path/position qubit (not the polarization qubit). I found this really strange as I thought half waveplates only affected polarization.
How can a half-wave plate affect the position qubit and not the polarization qubit?