# 3. Superposition

## Contents

# 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.