What's the difference between a set of qubits and a capacitor with a subdivided plate?

Question

This is probably just a misunderstanding on my part, but everything I've seen on what quantum computers do thus far seems to suggest that the actual process of reading the entangled qubits would be equivalent to reading the value of a plate opposing a subdivided plate in a plate capacitor while the setting of initial qubits would be the equivalent of assigning a voltage to each subdivided plate. E.g. in this image:

You would be able to read the voltage on the red plate after setting independent voltages from a known range representing 0 at the low and 1 at the high on the 4 separate subdivisions of the opposing plate, then rounding off at some particular voltage to get a zero or one out of it for those 4 bits.

Is this wrong? If so, how does it differ from actual quantum computing?

Answer 1

Your capacitors cannot be in the state $\frac{1}{\sqrt{2}}\left(|00\rangle + |11\rangle\right)$, but qubits can.

Let's say $|0\rangle$ is 0$\,$V and $|1\rangle$ is 1$\,$V.
If you have 2 bits we can have $|00\rangle$,$|01\rangle$,$|10\rangle$,$|11\rangle$.

But the state: $\frac{1}{\sqrt{2}}\left(|00\rangle + |11\rangle\right)$, is in a superposition of two of these cases. The bit values can be (0,0) or (1,1). Either case is equally possible, until a measurement is made (think Schrödinger's cat: you don't know if it's alive or dead until you open the box).

Answer 2

It looks like you are asking about the possibility of encoding the mathematics of quantum states & measurement into some kind of analog device. And yes, I think this is possible. This reminds me of how people study analog models of gravity. The one problem I can see with this is that it will not scale very well as you increase the number of entangled quantum systems. Eg. for every extra qubit added to a system you double the number of dimensions. So for 10 qubits you would need a capacitor plate with 1024 subdivisions, and so on.

In summary, what you are proposing is to simulate a quantum system with an analog computer. We already do this with digital computers, but it just doesn't scale.