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Quantum Computing Simplified

The views expressed are those of the author and are not necessarily those of Scientific American.


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We live in a world where technology is changing rapidly. We are facing new technologies daily. These technologies are changing our lives and helping us to live better. One technology that is constantly changing is the computer. For years, we have used these miraculous devices in cars, banks, at work, home, and in school.This type of computer has been known to us as the “classical computer”. The first classical computer was developed in 1936. Now with the onset of the 21st century, we are looking at a new type of computer. This computer is called a “quantum computer”.

So why the quantum computer? When we refer to “quantum”, we are talking about atoms and molecules. The properties of atoms and molecules allow us to be more precise in measurement and processes. So to have a computer made of atoms and molecules, we can do tasks that are faster, more accurate, and more refined. It can help us to be more precise in a GPS with location, be more refined in the composition of images and faster in processing results. Think of a digital camera. If you have two which are identical; but one has more pixels than the other, the image is clearer.

This is the same with quantum computing, the more qubits, the better the result. Quantum computing is based on quantum mechanical concepts. To understand quantum mechanics, we need to shrink down to the size of atoms and molecules. We need to understand how the atoms (or molecules) interact, what causes them to interact, and why they interact. We need to understand the rules or laws of quantum mechanics just like understanding the laws or rules of Chess. The history of quantum theory dates back to 1838. Old quantum theory states that the motion of an atomic system( a group of particles) is quantized. When referring to quantized, this means to limit the properties of the whole which is given a specialized set of numbers that are described by quantum mechanical rules. To understand this, let’s go shopping in the juice aisle at the store. There are several different kinds of juice in the aisle but what makes them different? If we pick a can of orange juice and can of cranberry juice, we can see that some of the ingredients are the same but some of them are different.

These different ingredients (or properties) distinguish the orange juice from the cranberry juice. The atoms on the periodic table are just like those different types of juices. Each atom has a set of ingredients we call quantum numbers.

The first quantum number is the energy level. The energy level can be thought of as the flavor of the juice (orange or cranberry).The second quantum number is the angular momentum.This number would tell us how concentrated or how strong the flavor is.The third quantum number is the magnetic quantum number. This number determines the strength of the second number. It would represent the ingredients that determine the concentration.The fourth quantum number is the spin quantum number. This number determines the flavor of the juice.While the other numbers are similar, the fourth number is the difference between the juices. Yes, there are many more quantum numbers but these are the four basic ones(the four basic ingredients).

Angular momentum is at the heart of quantum theory. Angular momentum is the quantity of rotation of a body. This is the mixture of the moment of inertia and angular velocity. To think about angular momentum,One basic example is a ball spinning on your finger. Sounds familiar? Yes, just like the earth, atoms spin on an axis too. This moment of inertia is defined by their mass and the volume that the mass occupies. Let’s take the ball and fill it up with one of the juices; you know, just like a balloon with water in it. Now, let’s squeeze the ball and we change the state of inertia( the ability of the mass to have rest). When this happens, they have angular velocity. Angular velocity is how fast the angle changes with respect to time. Over the years; as quantum theory developed, angular momentum would become the center role of understanding quantum theory and would be given the name of Planck’s constant.

Planck’s constant is influential to the three key concepts of quantum computing. These three concepts are superposition, entanglement, and coherence. Superposition happens when two pure states form a mixed state. This state is a quantum
system. The quantum systems include the energy level, angular momentum, spin, position, polarization, and momentum. One way to look at superposition is to imagine a glass of orange juice and a glass of cranberry juice. Mix the two together and you get superposition (a glass of cranberry orange juice). The same thing happens when two quantum systems combine.

Notice that the tastes of the cranberry and orange juice do not change but rather they are “added” together, the same happens in superposition. The properties of the states do not change but rather they are “added” together. Entanglement is a form of quantum superposition. The entangled states appear as one state until separated or until one is measured. Let’s say we have two twizzlers that are joined together because they have similar properties. One twizzler is orange and the other is cranberry. When you pull (energy) the twizzlers apart, they separate and move in opposite directions. The properties that these twizzlers have in common remain unchanged; however, note upon separation, that the properties on both strings may be in different locations on each twizzler.

Coherence happens when a group of particles are acting together in a single quantum state. Basically, two pure states combine to make a mixed state.  Ok, so let’s follow the steps:

1) We have two pure states: The orange juice and the cranberry Juice.

2) We combine the juices together. The juices become “entangled” or superimposed with one
another.

3) Upon this superposition or entanglement, they cohere with one another and become a mixed state.

The mixed state or two-body state gives rise to the definition of the qubit or the quantum bit, the fundamental unit of quantum computation that a quantum computer is based on. In computers, we have the unit of the bit( “binary digit”). The bit can have the value of either 1 or 0. It is a variable that can have only two possible values. However, the qubit; because of the idea of superposition that we discussed earlier, can have two bit values at once. Once again, consider our qubit as a combination of cranberry juice and orange juice.They both have certain properties in common; however, one is orange and the other is cranberry. When they are united, they create a superposition and form a ‘qubit” of information.This quality of quantum computing enables faster processing and more refined results in a ‘qubit” of information. These refined results are much like the pixels in a digital camera;the more pixels, the cleaner the picture. Likewise, the more qubits, the better the computational result.

You might be wondering one thing:computers get viruses but what about quantum computers? The answer to that question is another topic but here is the short of it. Quantum computing uses “quantum error correction” which requires hidden variables to protect the quantum programming. These hidden variables are like using a container for the cranberry orange juice or putting the cranberry orange juice in the refrigerator to keep it cold and protected from viruses.

One unique quality of quantum computing is that can be used to study the mysteries of quantum mechanics. In the near future, quantum computing will have uses for the quantum teleportation of information, biological studies, and cyber security.

Joel Taylor About the Author: Joel Taylor grew up in Siskiyou County, California. He attended Yreka High School in Yreka, California. After that, he attended College of the Siskiyous in Weed, California and then transferred to Southern Oregon University in Ashland, Oregon where he graduated with a Bachelor's of Science in Physics. Since then, he has had his own tutoring and research company. He has also worked at the Maryland Science Center in Baltimore, Maryland. Joel is also a member of the American Physical Society and American Institute of Physics. Follow on Twitter @Joel_a_taylor.

The views expressed are those of the author and are not necessarily those of Scientific American.






Comments 1 Comment

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  1. 1. ABlack 11:21 am 12/13/2012

    I’ve often heard the phrase quantum computing used but this is the first time it’s been properly explained in language that I can just about fully understand.

    Link to this

    Link to this

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