Quantum Computing: An Informative Introduction
Quantum Computing, a current buzzword, meandering for more than one decade, is now a reality. Honestly speaking, when I first hear about Quantum Computers, I thought that it is based on a drastically different mechanism, which it is and also is always super powerful than classical supercomputers, which is wrong. Quantum Computers are made using the bizarre nature of Quantum Mechanics, which even Einstein never was very fond of (because it was NOT matching with the Theory of Relativity 😆). Now in this article, I will clarify to you what Quantum Computer is, its principle, and its applications. Here are the topics of this discussion —
a. Classical and Quantum Computers.
b. Principles of Quantum Computer.
c. Why & in which condition it outperforms a classical computer?
d. What are its application domains?
e. What Next?
Before jumping deep into our quantum world, I want to clarify that this article is mainly intended for anyone who possesses basic knowledge of science, i.e. high-school students, newly joined college freshers, and someone who wants to join this field, but had a different field before.
Classical and Quantum Computers
Before directly jumping into the Quantum world, let’s talk about the classical world, and then we will make a smooth transition to the quantum world. The principles of classical computers are evolving for more than a century now, starting with sir Charles Babbage, and dating back to the late 1900 century. This was one of the earliest computers, and later sir Alan Turing came up with his brilliant idea of the Turing Machine, who laid the foundation for not only modern Theory of Computation, but also modern Computers. This Turing Machine (TM) is a mathematical model, which proves that there is absolutely no formal way (namely algorithm) to tell that given a TM and an arbitrary input if the program will ever halt/comes to a definite answer or not. All our everyday computers to supercomputers are following this TM only.
Supercomputers are computers with lots of CPU and GPU cores, which can do much more parallel processing than our normal computers. We generally tend to use supercomputers when we are working with very complex problems, where we have lots of computation power required. Keep in mind that these overly powerful computers can even work with petabytes (10,00,000 GB) of data, and there are problems, where we need more computation power required. For example, modelling the behaviour of an electron inside an atom is a tedious task even for supercomputers. Sir Richard Feynman once asked this question in his paper “Simulating Physics with Computers”,
What kind of computer are we going to use to simulate physics?
Our observable universe can not always be described as classical, and on a subatomic level, things behave differently. Hence we need some sort of device to simulate that too. That is one reason for the advances of Quantum Computers. Well, there are other reasons too, and those we will discuss in the later parts. It is now time to learn about the principles of the quantum computer.
Principles of Quantum Computer
Quantum Computers work on a few strange principles of Quantum Mechanics. But what is Quantum Mechanics exactly?
Quantum Mechanics is a field of physics, where we discuss the behaviours of subatomic particles like electrons, protons, neutrons, etc. Believe me or not, but at the subatomic level, things behave very differently than in the classical world. To understand this quantum behaviour, we need to study this quantum physics.
The main principles of Quantum Mechanics are Quantum Superposition, Quantum Entanglement, and Quantum Interference. Let’s discuss each principle one by one.
- Superposition — This concept can be simply explained as a particular object being present with more than one state at a single time. For example, Schrödinger’s cat. Sir Erwin Schrödinger told us about one scenario, where a cat is stuck in a box, and there will be one radioactive material inside that box. As per nature, the radioactive material will decay, and when it decays, the poison will be triggered to release, which will eventually kill the cat. Now we can not see those happening inside the box, and from outside, the cat is dead as well as alive at the same time until we open the box and check out what is happening inside. So, the cat is in two states at once, which is a proper example of superposition. One thing to notice is that when we open the box, the states will collapse into one state, and we can check out if the cat is either alive or dead.
No Animals were harmed in this hypothetical experiment.
The spinning coin is in the superposition of both head and tail, as we can not separately tell if it is in head or tail.
- Entanglement — This is a weird correlation between two quantum objects. These objects can be any particle, and in this correlation, these two particles/objects will share a link between them, no matter how far they situate in space. Also, their states will correlate too in this entanglement. Let’s understand this with an example, suppose you cut two sides of a coin. Now you have one side, but gave the other side to your friend, and told him to travel to the end of the universe. Your friend does not know which side he has, but if it is for sure that if he has the head, then you have a tail, and vice-versa. Hence a correlation is formed between you and your friend. When your friend will open the box, instantly he will know the status of your coin. Einstein named this “Spooky action at a distance”.
Please Note that knowing the status of your coin, your friend may think that the information is traveling more than the speed of light, but the information is NOT traveling faster than the speed of light.
- Interference — Interference simply means that two waves are interfering with each other. Now this interference can be of two types, 1. Constructive Interference — Here when two waves are passing by together, the top, as well as down peaks of the waves, will match, hence the top peak and the bottom peak will sum up, making a constructive interference. 2. Destructive Interference — Here when two waves will pass by, the top and bottom peaks will match reversely to that of constructive interference. For example, the top peak of the first wave will match the bottom peak of the second wave, and vice-versa.
These are the 3 main principles or postulates, on which it will work. But unlike traditional computers, we will not be working with bits, which are strings made of regular 0s and 1s. In general, we can represent these bits using transistors, when a transistor is on, it is denoting 1, else 0. But in quantum computing, we will be working with qubits, which is a combination of states 0 & 1. With 1 single qubit, we can make 2 states 0 & 1, so it is basically declaring the probability of being a state in 0 or in 1. Now important is that this probability can be 50–50, or 40–60, or even 99–1, but the sum of the probability of 0 and probability of 1 will always be 1. With 2 qubits, you can make 4 states, 00, 01, 10 & 11. With 3 qubits, you can make 8 states, 000, 001, 010, 011, 100, 101, 110 & 111. These exponential numbers (2^n) of states is giving us the power that we need to calculate.
But how are the qubits following these quantum principles? First, given a single qubit, it can stay in two possible states (0 & 1) until it is seen or measured. This is a phenomenon called Superposition. Second, a pair of qubits can be in an entangled state, where changing the state of one qubit will surely change the state of another entangled qubit in an anticipated manner. This is the use of Entanglement here. Thirdly, Interference is used to manipulate the quantum states of a qubit. Basically, these can change the probability amplitude of a state, and by changing it we can manipulate the states of that qubit. We represent a single qubit as a block sphere, where a block sphere represents two states 0 & 1. The north pole represents the state 0 and the south pole represents the state 1. Also, this sphere can tell us about the state of the qubit, we will study more about this when we study the quantum gates individually.
** To perform some computation with these qubits, we need some sort of gates just like a traditional computer. For example — AND, OR, & NOT gates can perform some computation in classical computers when applied with some binary bits. Likewise, we have few gates, that can do the same in this domain, and these are different than the classical gates. I will name a few gates here, but we will study them in a separate post.
- CNOT
- Hadamard
- Pauli-X
- Pauli-Y
- Pauli-Z
- Phase, etc.
A very important point about these gates is they are all reversible, unlike the traditional gate. All classical gates are not reversible, for example —
0 AND 0 == 0 AND 1 == 1 AND 0 = 0
Hence if someone gives us the result as 0, we will be able to say for sure that this was the input. But this is NOT the case for these quantum gates, they must be reversible.
Why & in which conditions it will outperform the classical computers?
There can be quite a few of you, who can ask this question, is the future will be all about Quantum Computers? or Will regular computers be of no use after say 10 years? The answer is a strict NO. Quantum Computers will be developed, and certainly, they will outperform regular computers, but it is very obvious to understand that it works better given a particular set of problems, and not all. I will discuss some of the domains, where we can use this technique in the next chapter, but here we will discuss, which are the particular sets, where we can apply this problem.
The future will be purely Classical-Quantum in nature, as for the regular day-to-day work, we will still be using classical computers for sure. In those tiny matters, Quantum Computers will not be going to show any supremacy, but rather may show inferiority. So, the problems, where we have lots of variables to deal with, and count numerous other factors, there only this computer will show its actual power.
One such example is the shortest route finding, where given a state, you have to touch all the cities, also start & end at the same city. But the problem is you have to do that in the shortest possible distance. In this problem, we have a lot to deal with, there are multiple routes from one city to another city and all. Once the number of cities increases in the state, the complexity will increase exponentially. There can use Quantum Computing to solve this problem, as it can leverage the superposition property, to check multiple routes from one city to another and give us the optimal.
What are its application domains?
As told before, it can not always outperform the regular classical computers, but Quantum Computers are used in some special areas like —
- Simulating a molecule — Simulating the behaviour of a molecule like an atom is a tedious task for supercomputers, as a molecule can be in anywhere in space, and we need a tremendous amount of power to simulate them.
- Drug discovery — Discovering a drug takes at least 10 years, and with these special computers, we can drastically increase the speed as we will be able to simulate the chemical particle natures, which are needed to make the drugs.
- Cryptography — A Quantum Computer can easily break a 2048-bit RSA encryption in a few hours of time, and if we can make encryption with these computers, then it will be almost impossible to break even for the fastest supercomputers.
- Finance — It has its own application in the domain of finance as well. The main applications include making financial predictions, fraud detection, risk management, etc.
- Machine Learning — With the help of these types of computers, we can easily train our models more accurately, and make better models. We can handle very large datasets with this computer.
- Physics — Since physics is all about studying the fundamentals of nature, hence with it, you can simulate nature and start studying it more accurately.
So, I guess now you have understood that there is some set of problems, for which the fastest supercomputers will take millions of years to give output, and due to its quantum behaviour, it will give us drastically fast results. That is why it is necessary for us. In general, it is very important for us to understand its potential use cases to develop some technology, and that is what we did in this section.
What Next?
Congratulations, now you have stepped into the world of Quantum Computing, and trust me, this is just the beginning. There are tons of opportunities out there to learn and explore. Below I will mention some of the cool stuff, which you can read and learn about it —
- Supercool introduction to Quantum Computing by David Cogen — https://www.youtube.com/watch?v=zhQItO6_WoI
- An introduction to Quantum Information and Computation by Qiskit (a quantum programming language by IBM, written in python) team — https://www.youtube.com/watch?v=3-c4xJa7Flk
- Quantum Computing explained by Quanta Magazine — https://www.youtube.com/watch?v=jHoEjvuPoB8
- The biggest discovery of 2022, which is making a wormhole in a lab using Quantum Computer — https://www.youtube.com/watch?v=uOJCS1W1uzg
These are some of the tech corporations, that have made their own Quantum Computers, —
- IBM — They are leading when it comes to Quantum Computing, as they have made IBM Quantum System One, which is one of the first commercial Quantum Computers, available in the market. Their own programming language to program their Quantum Computer is called Qiskit, which is a library of python. Anyone can access their computer, as they are hosted in the cloud. Currently, they have made a 400-qubit processor.
- Google — In the year 2019, Google demonstrated Quantum Supremacy using a 54-qubit processor named “Sycamore”. It basically shows that it can perform a complex computation in 200 seconds, whereas a powerful supercomputer will take more than 10,000 years to complete. They wish to make a fully functional universal Quantum Computer by 2029. Google’s programming language to program this computer is called Cirq.
- Microsoft — They are also not too far behind, as we now have a full-stack Quantum Computer, which we can use using Microsoft Azure. Even Nasa’s JPL uses its Quantum Computers. The specialty about them is that their qubits have a lower error rate compared it’s competitors, thanks to the topological qubits, which they have developed.
- Rigetti — Rigetti is one of the popular names when it comes Quantum Computing industry. They utilize the full potential of superconducting qubits, which are regular atoms, generally kept very cool (-273 degree celsius) inside dilution refrigerators. They are stored at such temperatures because they use entanglement to couple qubits together, and since interaction with the smallest particle can collapse the entanglement, hence they have to store them in such low temperatures (0 kelvin = -273 degree celsius), where there are no active photons in the environment.
If you are still here at this moment, then I will give you one bonus tip, by which you can study and learn more systematically. Here is one Quantum Computing course offered by Qubit By Qubit, which is by far one of the best courses available in the market. Here is the course link, if you want to check it out,
Also, I would like to wish you the best for the journey into Quantum, and from this post, I hope that you have gathered pretty strong foundation knowledge to explore more depth in this field. May the force always be with you. 🔥
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