3. Superposition



From the video, we learnt that superposition is when a quantum object can be in two or more different states at the same time.

To simplify things, we looked at only two-level physical systems. Two-level systems have two possible measurable states. This means that when we observe or measure the system, we can get one of two posibilities. Technically, we can have a superposition of not just two states but as many as there are for that quantum system.

Superposition is cool because it is a behaviour that is associated with waves, and so it is a direct reinforcement of the dual wave-particle nature of quantum objects.

Here’s a cool idea on superposition…

Shrodinger’s Cat in a Box (Pt.1) – A Superposed Quantum Cat

Erwin Schrodinger posed an interesting thought experiment to illustrate the wonders of quantum superposition. The beginning of it goes something like this…

Imagine you have a cat in a box.  It’s a quantum cat, obviously.
Well, Quantum Mechanics states that the cat can be in a superposition of more than one state at the same time.
The cat being alive or dead is the perfect example of a two-level system by the way. The cat can either be in the alive state or it can be in the dead state.
However for our quantum cat, it can be both alive and dead.

So what do we, as classical observers, see when we look at the cat? (And why is the cat in a box?)

I’ll give you some time to think about these questions, and we’ll continue this thought experiment in the next section.