I recently came across 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).
Since my only knowledge of quantum computing comes from this online textbook: https://qiskit.org/textbook/ch-states/introduction.html, which doesn't focus on the underlying physics), I was having trouble understanding the underlying physics used in those 2 videos.
I will try to explain the device's function in my own words. Please critique any incorrect statements I make.
2 qubits are encoded using a single photon.
Qubit 1's state is described by the path the photon is on and Qubit 2's state is described by the polarization of the photon.
Once the photon has passed from the laser past the 1st polarizing filter and beam splitter, it is equivalent to a Hadamard gate being applied to both Qubit 1 and Qubit 2.
After the photon passes through the waveplates, it is equivalent to the quantum oracle being applied to both Qubit 1 and Qubit 2.
Lastly, the photon passes through one final beam splitter, which is equivalent to a Hadamard gate being applied to both Qubit 1 and Qubit 2.
The difference in the interference pattern on the wall shows whether the quantum oracle was balanced or constant.
Am I interpreting this experiment correctly and can someone explain the physics underlying this system? I found the two videos to be very confusing, although very fascinating.
Thank you very much for your time and I apologize for the long question.