Quantum Computing Explained: Will it replace traditional computers?

Ever wondered what is a Quantum Computer and when you will be able to buy one for yourself?

This article is here to answer all your questions. But first, here’s a gist for those of you who are in a hurry.

The performance of classical computers is still increasing at a significant rate. Moore’s Law might have slowed down but it isn’t dead yet but it soon will. The size of transistors is fast approaching the physical limits. Quantum computing is something that has the potential to solve this problem. It is an entirely different approach to computing, which is not limited between the 0s and 1s. In a way, quantum computing is about anything and everything between 0 and 1. If this sounds confusing, you are on the right track in understanding quantum computing.

Read on to find out what it is all about.

Let’s begin with the basics.

Quantum physics is the study of the properties of mass and energy at a subatomic level. The behavior of the subatomic particles is entirely different from what you expect it to be.

According to quantum theory, the properties of a system like energy and momentum are quantified. The values that these properties can take up is restricted to some discrete states. These packets are called quanta and are indivisible. In quantum mechanics, every quantum entity exhibits properties of both waves and particles.

Max Planck, Albert Einstein, Louis de Broglie, Arthur Compton, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, and many more physicists have proved that all particles exhibit wave nature and vice versa.

Here’s an excellent video by Kurzgesagt – In a Nutshell, to understand Quantum Computing in just 7 minutes:

Video Credits: Kurzgesagt – In a Nutshell

    Basics of Quantum Computing

Before we jump into the working of quantum computers, let us look at some technical jargon from the world of quantum mechanics. Having a rough idea about all these terms would help us understand the working of quantum computers.

Schrödinger’s cat

This isn’t a technical term, rather a very famous thought experiment by Erwin Schrödinger and it is often considered a paradox. The thought experiment involves putting a cat in a bunker with an unstable compound that has a 50% chance of blowing up and a 50% chance of doing nothing at all.

It is not until we look into the bunker; we can find out whether the kitty is dead or alive. When we do take a look, it is either dead or alive, but not both. If we repeat the same experiment a large number of times, we will see that half of the time, the cat survives, and the rest of the time, it is dead.

Erwin Schrödinger’s interpretation is that before we look into the bunker, the cat is both dead and alive. The act of looking into the bunker forces nature’s decision.

From the cat’s perspective, she either sees the compound explode or not. These are the only two possibilities:

  1. The compound explodes, and the cat dies.
  2. The compound does not explode, and the cat survives.

It is impossible for the compound to explode, and the kitty does not see it explode. So the kitty’s reality becomes entangled with the experiment. It is our observation of the experiment that forces nature to collapse the reality to one of the two possible outcomes.

We are like the cat too; we open the bunker and either see the cat die or find it alive. It is not possible for us to see the cat, both dead and alive. In essence, we are entangled with these outcomes. There might exist a bigger multiverse in which both the possibilities happen in parallel, but what is forcing us to arrive at our reality? This is probably the biggest unanswered question in the entire quantum physics.

Here is a video by minutephysics explaining more about the Schrödinger’s Cat experiment: 

Video Credits: minutephysics

Überlagerung: Superimposition

Similar to waves in classical physics, quantum superimposition is a phenomenon in which the coexistence of multiple quantum states is possible.

A quantum system can exist in several different quantum states all at the same time. Only if we measure the quantum property, it takes a form of one of the possible quantum states.

Verschränkung: Entanglement

Quantum entanglement is the phenomenon observed when the quantum particles, present at particular proximity to each other, get linked in such a way that it becomes impossible for either of them to exist in different states at the same time.

What this simply means is that both the quantum particles get entangled in such a way that both of them are in perfect synch. Changing any one property of one particle has a direct effect on the same property of the other.

Dekohärenz: Decoherence

In a non-isolated quantum system, quantum particles give up their superposition and collapse to a definite state during the measurement of a quantum property. This creates a possibility for us to measure the exact outcome of the function, which we are looking for, often the solution.


A binary digit or a bit is the smallest unit of storage. It is a memory element that can either hold a value of 0 or 1. A bit can be realized by something as simple as a switch or a complicated network of electronics depending on the system, which utilizes the memory element.

Qubit, on the other hand, is the most fundamental element of a quantum computer. The difference is that a qubit, being a quantum property of a quantum particle, can exist in different quantum states simultaneously.

Qubits vs Classical Bits

Qubits exhibit the quantum properties of superimposition, entanglement, and decoherence.

You can learn more about Qubits with the help of this video by Veritasium:

Video Credits: Veritasium

    The Quantum Supremacy

Quantum Supremacy is a term first coined by the theoretical physicist John Preskill in 2012. According to Preskill, it is a point at which the quantum computers can perform a computation which a classical computer can not manage. This would be a point when a quantum computer would beat the best classical computer in existence.

There have been several attempts to prove the quantum supremacy. Companies working in the field of quantum computing have come up with insanely complicated computations, which are incredibly difficult for classical computers and favor their quantum counterparts.

This would let the quantum computers perform calculations way faster than classical computers. What may take thousands of years for classical computers may be a matter of a few minutes for a quantum computer.

In the following sections, we will list out some popular quantum algorithms. However, there are hardly any applications of quantum algorithms that are of any use to us today.

    Quantum Algorithms

There are several quantum algorithms that are used to solve a particular problem. Deutsche-Jozsa algorithm is one of the oldest and amongst the first few quantum computing algorithms ever made. The problem solved by the Deutsche-Jozsa algorithm is designed in such a way that it is challenging for classical computers to solve.

A set of binary values are fed to a black box which either generates a constant output or a balanced output. Dusche-Jozsa algorithm is used to find whether the given oracle generates a constant output or a balanced output.

Apart from the Deutsche-Jozsa algorithm, there are some other algorithms that are pretty popular. Simon’s algorithm and Bernstein Vazirani’s algorithm are among the ones that are worth mentioning. Some of these algorithms have led to the development of quantum Fourier transform, the quantum analog of the discrete-time Fourier transform.

These algorithms have little to no real-life applications. However, the two algorithms which do have the potential to change the modern-day computing are the Shor’s algorithm and Grover’s algorithm. The factorization of large numbers is probably the biggest problem in the entire history of mathematics and computer science.

Shor’s algorithm deals with the factorization of large numbers. Shor’s algorithm is faster than the general number field sieve, the fastest known algorithm for factorization of a number that is more than a hundred digits long.

It would be practically impossible for even the most powerful classical supercomputer to find factors of a number that contains over a thousand digits. On the other hand, a quantum computer can possibly arrive at a solution to such a problem.

The factorization is the basis for public-key encryption algorithms like the RSA encryption. Shor’s algorithm on a quantum computer can prove as a severe threat to such systems and can arguably render such encryption completely useless.

Imagine a hacker being able to hack into every bank account with his quantum computer. It is as scary as it sounds.

Another very well known algorithm that might establish quantum supremacy is Grover’s algorithm. It is a quantum algorithm that finds the unique input value to an oracle from a particular output value.

Grover’s algorithm is a lot faster than linear or sequential search. It is the fastest quantum algorithm that can be used to search an unsorted database.

Qiskit Aqua

Image Credits: Qiskit 

Qiskit Aqua is an open-source library of Quantum Algorithms. Here the Aqua stands for Algorithms for QUantum computing Applications. You should check it out if you’re into Quantum Computing.

    The Real Power of Quantum Computing

Here are some applications of Quantum Computing:

Predictive Analytics

What most of us know as Artificial Intelligence, Machine Learning, Big data, or Data Science, everything falls under the category of predictive analytics. It can be applied to a variety of fields like weather forecasting, computer simulations, finance, and stock markets, and probably everything you can think of.

Having a working quantum computer could prove to be a considerable step forward in predictive analytics and a massive jump in the field of computer science.

Medicine and Healthcare

Simulating something is very resource-intensive. Being able to simulate the behavior of molecules and chemical reactions may prove to be something of great importance in the field of medical science.


We have discussed the effects of Shor’s algorithm in the world of cryptography, but thinking from an optimistic perspective, Shor’s algorithm can become a basis for future encryption algorithms. In the right hands, it can be used to build encryption techniques that are impossible to break; at least for a very long time.

Either way, one thing is sure, when the first commercial quantum computers arrive, cryptography is set to receive a complete overhaul.

Understanding Quantum Physics

Simulating a quantum phenomenon should not be an issue for a computer that is built on the same technology. Quantum computers can simulate the behavior of quantum particles and molecules easily, for which classical computers have struggled from the very beginning.

Being able to simulate quantum behavior can open a world of new possibilities. It can lead to the discovery of something about which we might have no idea today.

    Will I ever get a quantum computer?

Quantum computers are not going to replace classical electronics. They are intended for those problems that classical computers either can’t solve or take unreasonable amounts of time.

We are still at a very early stage to comment on anything about the exact time when we might start seeing quantum computers in the market. There are also chances that the day might never come and they stay restricted for research purposes.

In the field of quantum computing, we are still at a stage where we are using punch holes to store the data. It will be long until we arrive at the NAND flash storage generation.

If you are curious about this technology and wondering if you will ever be able to purchase and use a quantum computer, then the answer may disappoint you. The answer is both a yes and no. While you may not get a chance to own a quantum computer in the foreseeable future, it is possible to access quantum computers over the cloud even today.

Developers do test out their programs on quantum computers available through the cloud. Software giants like IBM, Google, Amazon, and a lot of other companies let anyone work on their quantum computer and test them out firsthand.

    The Quantum Hurdles

There are a few problems that we need to deal with. To build a quantum computer that is superior to classical computers, we need to overcome some obstacles first. We need to find answers to a lot of questions; solutions to a lot of problems.

Shortage of researchers

With a population of over 7.5 billion, it is difficult to believe that we lack qualified professionals to research on a ground-breaking technology like quantum computing. There seems to be a lack of interest in such topics. Very few quantum physicists are dedicated to spending their time working on the development of quantum computers.

Viability of cryoelectronic systems and environmental interactions

A quantum computer harnesses the quantum properties of subatomic particles. The quantum processors need to be cooled down to temperatures nearing absolute zero (0 Kelvin) which is approximately -270°C. The availability of such environments is limited and achieving such low temperatures is difficult and costly.

Environmental interference may lead to unintended quantum decoherence in the qubits.

Error and reliability

The accuracy of quantum computers is really poor. It is not uncommon for bleeding-edge technologies like these to suffer from issues of reliability. We do not have the technology to control the quantum properties of the computer. The development of a reliable environment that lets us execute the quantum algorithms without errors is something that we all are striving to achieve.

Here is another video in which Dr. Talia Gershon (Quantum Research team, IBM) explains quantum computing in five levels of difficulty. Can you keep up till level five?

Video Credits: WIRED

    The future of Quantum Computing

We are still very far from being able to leverage quantum computers to solve real-world problems. Quantum computers will not be wiping out classical computers. Both technologies will co-exist for a long period.

With the pace with which we are moving towards that future, it wouldn’t be wrong to assume that we may start seeing fully functional quantum computers solving some real-world problems by the end of this decade.

However, one thing is certain: quantum computing is all set to change the very way we understand electronics, computer science, Quantum Mechanics, and the Universe.

So, does that mean we will continue using classical computers for decades to come?

The answer is most likely yes. However, the way classical semiconductor-based Computer chips are built will change over time. Soon, FinFETs will be replaced GAAFETs with Samsung’s 3nm Process and TSMC’s 2nm Process.

However, the major change will come when we hit the limits of silicon and need to switch to another material.

Graphene, Carbon nanotubes, and the Nanomagnets are some of the top candidates that might replace our Silicon-based Computer chips in the coming decades.

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