why is the Bloch sphere qubit representation inaccurate


why is the Bloch sphere qubit representation inaccurate

In: Physics

i can think of two ways in which you could say that the Bloch sphere representation is inaccurate.

First, it’s not a model of how a qubit actually exists. Qubits aren’t spheres oriented along an axis like how they’re represented with the Bloch sphere. But it’s not meant to be physically accurate.

Second, from what I remember Bloch sphere representations aren’t unique. For example, I believe that if you represent the Bell pairs as Bloch spheres, they are all represented as two qubits at (0, 0, 0) on the Bloch sphere. Even though the actual states are different. Also, I don’t believe that Bloch spheres can show which qubits are entangled with each other. If you have two qubits, both represented as (0, 0, 0) that doesn’t necessarily mean that they’re entangled with each other. They could be a subsystem of a larger system and are actually entangled with qubits in the larger system. Though I’m not 100% sure on that last part.