Previously, we have discussed how one can combine qubits by taking their tensor product to create a multi-qubit system. We will be revisiting that concept in this lesson. But before that, let’s discuss quantum spin. We must build some basic understanding of it, its quantization, and its measurement so we can understand quantum entanglement.
The spin of an electron or any other quantum particle is a physical property that we can measure just like momentum and position. Without going too much into the details, spin can be considered a quantum mechanical variant of angular momentum. Loosely, you can think of spin as a certain direction in space, e.g., up or down, associated with a quantum particle.
Like other observables in quantum mechanics, spin is also quantized (discretized), meaning that it comes only in specific packets. You would recall from the previous lesson on the postulates of quantum mechanics that measurements on observables output the eigenvalues of the operator.