Is the cat dead or alive? — Superposition
Introduction
I know that this isn’t exactly an “Astronomy” post but I thought it would be pretty cool to talk about superposition simply because it is a concept that boggles the minds of some of the brilliant Scientists today.
“Like the very quantum particles we study, we must be comfortable allowing our view of the world to exist in superposition”
- Kevin Michel
Schrödinger’s Cat
Let’s assume we have this random opaque box that we cannot see into unless we open it. Now, this box has a vial of poison that rests below a mechanism containing a hammer.
The mechanism is kind of faulty; there’s a 50% chance that it can fail, causing the hammer to fall onto the vial and releasing the poison into the box. Let us now assume we put a cat inside this box and wait for an hour.
Over the course of the hour, we have no way to know if the mechanism has failed, resulting in the cat’s death, or not. The only we can know for sure is if we open the box. Therefore, we say that the cat is both alive and dead.
This is the idea of superposition: Any object that can exist in two states at once unless it is observed is said to be in a state of superposition.
Confusing right? First of all, what does “observe” even mean? Well in this context, if you observe the object, you’re looking at which state it exists in. Hence, if you open up the opaque box, you’re observing the cat to see if it is in the “dead state” or “alive state”.
Once you observe anything that can be in superposition, it collapses to one of its possible states and essentially cannot go back into superposition again. For example, once you see whether the cat is dead or alive, it cannot go back into the state of being both dead and alive.
This cat experiment is known as “Schrödinger’s Cat”. A thought experiment that was posited by Erwin Schrödinger, a genius Physicist, in 1935.
I’m sorry cat lovers…
Superposition and the electron
Superposition sounds kind of impossible, it seems like it’s almost fictitious. How can something exist in two different states at the same time? Superposition isn’t imaginary however, Scientists have experimentally found many things exhibiting the properties of superposition, one being the electron.
If you’ve forgotten, the electron is a subatomic particle that lies in these things called orbitals which surround the nucleus of an atom. They are negatively charged and are so small they have negligible mass.
In 1801, Thomas Young performed an experiment which is now known as the “Double Slit experiment”. He essentially shined light through two slits and noted the properties. This experiment was again repeated in 1927 using electrons.
Let’s assume we shoot a bunch of electrons through two slits onto a screen. This is how we expect the screen to look like:
However, when scientists shot the electrons through the slit. They observed something completely different:
The pattern produced on the screen in the second image is known as a wave interference pattern. Hold on… aren’t electrons particles?
Yes and no. You see, here is an application of superposition in real life. We don’t know for sure if light is a particle or a wave. In Physics, we learn light as being a wave. In Quantum Physics, you’ll probably learn light as being a particle. It exhibits both wave and particle properties. This is known as wave-particle duality. However, if you observe the particle, it will collapse into one state.
The second image is a result of a property known as diffraction. Essentially, if a wave passes through a gap that is smaller than its wavelength, it tends to spread out and multiple waves will start overlapping against each other creating the interference pattern.
In fact, if you observe the electrons and conducted the experiment again, you would get the following result:
Superposition and qubits
The basic building block of any living thing is a cell. The basic building block of computers is the bit. The bit is short for binary digit. In essence, it is either a 0 or a 1. These bits help relay and communicate with various components of the computer to do stuff. You should read up on something called the fetch-execute cycle if you find this fascinating.
The computers we use right now are known as classical computers. Even the latest macbook is a classical computer because it works with bits. Bits have a defined state, it can either be a 0 or a 1.
Qubits on the other hand stand for Quantum Bits. Qubits are used in quantum computers and they exist in a superposition. They are both a 0 and 1 until they are observed. When observed, it will collapse into a 0 or 1. The way qubits work is a lot more complicated and probably warrants its own post. For now, it’s enough to understand that qubits use superposition and as a result can help quantum computers perform certain tasks and calculations that would either take a long time or be outright impossible for a classical computer to do.
There are three properties an object must exhibit for it to be considered a quantum object. One of these properties is that it must be able to exist in a state of superposition.
I hope you guys enjoyed this post!
Resources:
