Quantum computers: How do they work and why are they important?
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Neither quantum physics nor digital computers are new concepts to humanity. The former is almost a hundred years old while the latter is more than seventy. However, building a digital computer that utilizes the wonders quantum world is a relatively new one. The concept is so promising that reputable research institutions and tech giants such as Google and IBM have been investing serious effort and money in its research and development.
How do they work?
To explain how quantum computers work, we first need to talk about how traditional computers work. Traditional computers, as the name suggests, are digital machines that conduct computations. They use binary bits to store information and do calculations. On a physical level, the binary bits are the semiconductor switches that are in the processors of the computers. Depending on the current that they receive they are either in a “closed” or “opened” state. Our laptops, smartphones, tablets, and smartwatches have millions of these switches to handle the complex calculations required to perform the tasks we expect from them.
Having talked about traditional computers we are almost ready to talk about the quantum computers. Before we start, however, it is a good idea to touch upon quantum mechanics. Quantum mechanics is the branch of physics that explains how the universe works at the very small, i.e. subatomic, scale. At the subatomic scale, the particles don’t act the way that we expect them based on classical physics. There are mainly three bizarre behaviors that are relevant to quantum computing. The first one is the super-position. The super-position is the co-existence of multiple states. For example, let’s assume that one of our friends places a ball in an opaque box. We know that the ball is either blue or red. In the scales that we are used to, i.e. where classical physics prevail, the ball has a single color but we just don’t know it until we open the box. However, if the ball was at the sub-atomic scale, things would be different. The ball would have two colors, i.e. red and blue, at the same time until we opened the box. Once we opened the box, i.e. observe the system, one of the states would disappear and the ball would appear to have a single color. The second bizarre behavior is interference. According to quantum mechanics, the sub-atomic particles can be described as either particles or waves. This is called the wave-particle duality. Due to the wave nature of the sub-atomic particles, they can interfere with each other in a way that is no different than water waves. The last bizarre behavior is called entanglement. Unlike the previous two behaviors, the entanglement is difficult to visualize. It is a unique way the particles communicate with each other. The behavior of one particle determines the behavior of another related particle instantaneously. Going back to our ball example can help to clarify this a bit further. Let’s imagine that we have two balls instead of one. They are somehow “entangled” to each other and then separately placed in two boxes. Once we observe the color of one of the balls, the other one instantaneously becomes the other color even if no one observes it. To make things more interesting, this happens at a speed faster than the speed of light.
The quantum computers utilize these bizarre behaviors of sub-atomic particles to do calculations at speeds unattainable by traditional computers. To start with, the quantum computers use qubits instead of bits. The qubits are sub-atomic particles such as electrons or photons maintained at special conditions such as extreme cold temperatures to fully express their quantum behavior in a controllable way. In addition to the qubits, the quantum computers also use special algorithms to do computations in ways that extract the most benefit from the unique natures of the qubits. One common example that explains how a quantum computer attacks a problem differently than a traditional computer is the following. Let’s imagine that we have a maze and we want our computer to figure out the exit route. A traditional computer would code each route with a unique set of bits and then check each route one by one. On the other hand, a quantum computer would not necessarily check each route one by one. Utilizing the superposition of the qubits, the quantum computer would be able to check multiple routes all at once, finding the right route much more quickly or it would entangle certain qubits with each other and short-cut the certain calculations, again shortening the solution time.
Despite their benefits, the quantum computers have their flaws as well. The scalability, i.e. increasing the number of qubits, the utilization, i.e. developing effective algorithms, and the reliability, i.e. minimizing errors due to particles not acting the way we want them to, are the main areas that scientists focus on.
Why are they important?
At this point, you might be thinking why I should care about these futuristic machines. You should care for two reasons. First, they have a very wide range of applicability. There are potential use-cases across automotive, energy, finance, logistics, manufacturing, pharmaceuticals, and cyber-security sectors. Specific algorithms can be developed to conduct very detailed risk analysis in the finance sector while others can be developed to aid utility providers to optimize their grid load distribution. Second, the performance uplift that they promise is so great that it will be impossible to ignore them once they are fully operationalized. Experts believe that quantum computers will reach speeds so high that they will even be able to break common encryption algorithms such as RSA. As a result, companies will certainly look forward to adopting these machines. Because of these two reasons, we should care about the developments in the quantum computing area.
Sources:
https://www.ibm.com/quantum-computing/learn/what-is-quantum-computing/
https://uwaterloo.ca/institute-for-quantum-computing/quantum-computing-101#What-is-quantum-computing
https://www.technologyreview.com/2019/01/29/66141/what-is-quantum-computing/
https://www.scientificamerican.com/article/what-makes-a-quantum-comp/
https://www.sciencealert.com/quantum-computers
https://research.aimultiple.com/quantum-computing-applications/
https://analyticsindiamag.com/top-applications-of-quantum-computing-everyone-should-know-about/
