The Three Pillars of Quantum Computing
By: Sara A. Metwalli
Tags: Quantum Computing, Quantum Physics, Demystifying Technology, Technology, Science

The Three Pillars of Quantum Computing

The fundamentals of understanding how a quantum computer works

Image by Gerd Altmann from Pixabay

Quantum computing is one of those topics that people find very interesting yet quite intimidating at the same time. When people hear — or read — that the core of quantum computing is quantum physics and quantum mechanics, they often get intimidated by the topic and steer away from it. I will not deny that some aspects of quantum computing are incredibly puzzling and hard to wrap your mind around. However, I believe that you can understand the basics and the overall ideas of quantum computing without overcomplicating things. That is what I will attempt to do in this article and some upcoming articles about various quantum computing-related topics.

In this article, we will talk about the three fundamentals of quantum computing: superposition, qubits, and entanglement. These three concepts are the building stones to understanding how quantum algorithms do their magic and how quantum computing has the potential to solve some of the problems classical computers have failed to solve.

Now, let’s tackle each of them in detail…

Superposition

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Superposition may be the most famous quantum mechanics term ever! I guarantee you have heard of it before, not directly perhaps, but as the infamous Schrodinger’s Cat. In case you never heard of the one and only cat, Schrodinger’s cat, is a thought experiment that explains the concept of quantum superposition. It goes like this: assume you have a cat and a sealed bottle of poison in a closed box together. The question now is, how would you know if the poison bottle broke open and the cat died or if the cat is still alive inside the box?

Since you can’t tell for sure if the cat is dead or alive without opening the box, the cat is now in a state of superposition, which simply means it’s a 50/50 chance of the cat being dead or alive. That’s it! In technical terms, superposition is a principle — much as in classical physics — that refers to when a physical system exists in two states at the same time. Superposition is not an absolute term; that is, it doesn’t mean anything by itself; it instead refers to a specific set of solutions. The set of solutions differs based on your application and what you’re trying to achieve. Nevertheless, the most commonly used set of solutions is ALL possible solutions, also known as Hilbert Space.

In the case of Schrodinger’s cat, the solution space (all possibles states of the cat) contains only two states; the cat is either dead or alive, there’s no other possibility. Hence the superposition of that solution space is that the cat is both dead and alive at the same time, or in other words, the cat is 50% dead and 50% alive. If we were to put that in an equation form it will look like this:

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This equation represents the mathematical form of the superposition of both states of the cat (dead and alive) with a 50/50 probability. The probability of any state equals the absolute value of the square of the amplitude. In our cat equation, both states have the same amplitude of 1/√2. Which if we calculated the absolute square of will gives us 1/2, or 50%. We also notice that the 2 under the square root also represents the size of the Hilbert space.

So, our cat state remains a mystery, that is until we finally open the box. Once we do that, the superposition will collapse, and the cat will be either 100% dead or 100% alive.