# Introduction to Quantum Computing :: Part #1

Hello everyone, I hope you are having a wonderful week, day or month. My name is Thirsty-Robot a wannabe hacker that is not really into hacking. I enjoy it, but what I’m really into is theoretical computer science, and also programming. For the past 2 months I’ve been studying quantum computing, so why not teach it. This series will cover basic concepts of quantum physics and some theoretical math.

This post will cover:

- What is Quantum Physics
- History of Quantum Physics
- Schrödinger’s cat
- The Wave Function

If you have any doubt don’t be afraid of commenting this post and asking.

So let’s start…

## What is Quantum Physics

Since the birth of men we have been trying to uncover the truths of the universe. Plato, Aristoteles where in a way, the founders of physics and all sciences. They use to ask questions and tried to get answers, even Aristoteles tried to tackle the question of gravity (he was wrong lel), but at least he tried. Many man came across some questions and tackled them, persons like Newton, Galileo, Copernicus were the founders of classical mechanics, but later there was another questions, what is matter made of? And we came with the concept of atoms, a simple model at first, then it got more complex.

Atoms are a normal part of our daily life, they are everywhere because you are made of them, and not only you, but every object around you. When scientists started to try and uncover the secrets of these weird little dots that were floating around in space they found very weird stuff. This evolved into the field of quantum mechanics that we know today. (more about this in the history part).

Quantum physics study all the things we cannot simply see and measure, like particles and atoms. The smallest things in the universe are being studied in this field. Quantum concepts are hard to understand at first, but if you really like this let me tell you that is a beautiful challenging new world and you are going to have a lot of fun.

## History of Quantum Physics

The history of Quantum physics is mixed up with the history of chemistry. It started with the cathode-ray tube, then the Black Body radiation problem by Kirchhoff, consequently the Photoelectric effect and finally we have Max Planck.

In the 1900 Max Planck (famous for the Planck’s constant) presented a theory where he assumed that energy existed as individual units, like little boxes, instead of a constant electromagnetic wave. He called this little boxes “**quantas**”, this name was obviously very influential.

Other scientists came along, and used this theory to explain some of their theories.The most influential scientist (and famous) to use it, Albert Einstein, quoted this theory on his tackle on the Photoelectric effect problem.

Several theories came out, about the same time, one of the most important was by Louis de Broglie in 1924. He created the theory of wave-particle duality. Then in 1927 one of the most influential physicist on this field, Werner Heisenberg (yes, Walter White name is inspired by this guy) published **The Uncertainty Principle**, where he states a very famous quote:

“The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa.”

–Heisenberg, uncertainty paper, 1927

He predicted that the more you know about something, the less you know about another thing.

Finally (for now) but not less important, Bohr came up with the Copenhagen interpretation. According to Bohr’s theory, a particle, until it’s measured, is in every possible state at the same time, by measuring the system we make it collapse and forces it to only show one possibility. This is better known as **superposition**.

## Schrödinger’s Cat

In 1935 a Austrian physicist named Erwin Schrödinger came up with a visualization of the Copenhagen interpretation in everyday objects:

He called everyone to imagine a cat, poison, a geiger detector, radioactive material and a hammer into a closed box. The radioactive material so small that it only had a 50/50 shot of being detected over the course of an hour. If the geiger counter detected radiation, the hammer would smash the poison, killing the cat. Until someone opened the container and observed the system, it was impossible to predict if the cat’s outcome. Thus, until the system collapsed into one configuration, the cat would exist in some superposition zombie state of being both alive and dead.

But how do we call all of this possibilities? Well Schrödinger came up with something called **the wave function**.

## The wave function

The wave function is a mathematical way to describe all the quantum states (possibilities) of a quantum system, and is represented by the Greek letter psi.

The square root can be discarded by using **the Born’s rule** that yields the possibility by raising to the power of two.

## Conclusion

Quantum computing it’s not an easy field, it requires a lot of study and a lot of asking. If you have any question or correction go ahead and I’ll give it a shot. This are only the basics, on the next chapter we are going to start the main topic, quantum computing. There’s gonna be more math, so I recommend being familiar with vectors and some basic algebra.

## Reference

- https://wonderopolis.org/wonder/what-is-quantum-physics
- https://en.wikipedia.org/wiki/History_of_quantum_mechanics
- https://history.aip.org/exhibits/heisenberg/p08.htm
- http://philsci-archive.pitt.edu/3077/1/UR_BHL2006.pdf
- https://www.thoughtco.com/copenhagen-interpretation-of-quantum-mechanics-2699346
- http://www.iflscience.com/physics/schrödinger’s-cat-explained/