Schrödinger's cat is a [[Gedankenexperiment]] used to visualize [[superposition]] and [[Entanglement|entanglement]]. Commonly, it is only referred to as an example for superposition, but as we will see, it would not work without entanglement. But wait, we haven't even told you yet what the experiment is all about... So, let's start at the beginning. Let us set the stage: Imagine a box. In that box, we place a sample of radioactive atoms. They will decay over time, but since this is a quantum-mechanical process, we cannot predict when the atoms are going to decay. If the atom decays, this will be registered by a measurement device. Once the decay is detected a hammer falls onto a vial with poison. So far problem. The question whether the atom decayed or not, becomes more pressing when we also place a cat in the box and close the box. The cat and the atom are now in a peculiar superposition $\ket{\mathrm{Cat\ alive}, \mathrm{No decay}} + \ket{\mathrm{Cat\ dead}, \mathrm{Decay}}$ Here, we used [[Braket Notation|braket notation]] to show that the whole system is in a [[Quantum State|quantum state]]. It is not in a classical state, since we are not observing the cat-atom system. If we were to open the box, we would observe the system and the [[Wave Function|wave function]] would collapse to one of the options. Interestingly, the explanation of this setup only works once we take into account the [[Entanglement|entanglement]] between the cat and the atom. If the cat was in a mere [[Superposition|superposition]], but not entangled to the atom, the cat could be dead or alive independent of the atom's state. >[!read]- Further Reading >- [[Wave Function]] >- [[Entanglement]] >- [[Quantum Mechanics]] >[!ref]- References