Introduction of Concepts of Quantum Physics

Concepts of Quantum Physics

I think I can safely say that nobody understands quantum mechanics … Do not keep saying to yourself, if you can possibly avoid it, “But how can it be like that?” because you will get “down the drain”, into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that. – Richard Feynman.

I have thought a hundred times as much about the quantum problems as I have about general relativity theory. – Albert Einstein.

If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet. – Niels Bohr.

Sir Isaac Newton, Galileo Galilei, and many other scientists tried to explain the world around them by finding rules that could capture and predict its behavior. They contributed to the old way that human used to explain the world, which is called classical physics. Classical physics is still studied and used, because it has been successful at explaining things on large scales. However, there are incidents that classical physics cannot explain.

Quantum physics is the part of modern physics that talks about very, very small things in our world like molecules, atoms, and subatomic particles like electrons and protons! All our surroundings are made up of molecules and atoms, so in a way we can say quantum physics describes everything at a fundamental level. This is where classical physics breaks and can not give us solid explanations.

With all these said, quantum physics still has a long way to go, and there are yet more things to be discovered and explored in this field. Predictions of quantum mechanics have been shown to be extremely accurate through experiments. There is a great match between theory and experiments here. Quantum physics is not easy to comprehend, but we have been able to use it in a variety of ways and make useful devices that have a great impact on human life.

QUANTUM IN EVERYDAY LIFE

Although quantum mechanics seems to be a very hard topic to understand, it makes an appearance in almost every modern-day technology that is widely in use. Look at the picture below to get a sense of quantum every day!

Have you ever used a digital camera? How about a device with a GPS? Or do you have any fluorescent lights at home? Maybe you have played laser tag? If the answer to any of those questions is yes (which is very likely!), you have already used quantum physics without knowing about it. Let's dive more into the digital camera example.

When we take a photo using a digital camera, the light coming from our camera's flash or the environment goes toward the objects we are trying to capture in the image. The target object absorbs photons and reflects others. The photons are collected by the lens. The lens focuses them on a sensor that causes the emission of electrons. The electrons will be emitted until the shutter of the camera closes. These emitted electrons are stored as negative electric charges. The stored charges will then be converted to numbers or binary data with the help of a computer. When this binary data is printed out or sent to a computer, it will form an image that we can see.

We would not be able to make digital cameras without the knowledge of quantum physics. Quantum physics is the thing that helps us understand the behavior of photons and electrons and also enables us to make electron-sensitive sensors that can help us transfer photons to binary data.

Scale of Quantum Objects

The things you are most familiar with - like books, cars, food, and so on - all are described by classical information. Where in the world can we find quantum information?  

Quantum information is contained in 'qubits', which are the quantum version of a classical computer 'bit'. Things that are very cold, or very small are described by qubits and can store qubits. This includes some of the weirdest things out there! For example, superconductors can be used to store qubits. Single atoms or even single electrons also store qubits. We will have a chance to explore some of these objects tomorrow. Superfluid 

A brief history of "Quantum"

In the 17th century, Sir Isaac Newton came up with a set of laws that could explain many physical phenomena. In the centuries that followed, more physicists followed Newton's path and elaborated on that set of laws, as well as offering new laws that would comply with the previous ones to explain even a more diverse set of phenomena. By the 20th century, some people thought knowledge of physics was complete and there was nothing left to be discovered in this field. This was something that the young physicist Max Planck was also told by one of his professors. But was that true? Should young physicists like Planck have be satisfied, and stop looking for new rules to describe the world surrounding them?

 Have you ever wondered why the sun is yellow? Or why do different materials have different colors when they are heated? Light bulbs emit light by heating a piece of wire until it glows - how hot do you think that piece of wire should get to commit the perfect yellow light we desire? These were the types of questions Max Planck was struggling with as a theoretical physicist. According to the laws of classical physics, the color of the light a heated object emits depends on its temperature. The hotter it gets, the further it goes along the light spectrum towards ultraviolet. The human eye can not see ultraviolet light so if we heat a piece of metal enough to emit just ultraviolet, it must disappear! However, we can still see extremely hot objects (like stars!). So what is going on? 

Classical physics could not give a reasonable explanation. That was when Planck understood he might set aside the laws he used to think can totally explain our world and think out of the box. According to classical physics, the light was a wave. Its energy depended on its frequency and this meant that its energy level could be any continuous amount. This was when Max Planck stepped in and wondered what if light could take only certain amounts of energy? E.g. it could either be 1 unit of energy, 2 units of energy, 3 units, and so on, and no amount between these? These energy levels were called quanta and more research around them leads to the birth of quantum mechanics.