A Journey from Classical to Quantum Computers

by Abhishek Verma and SS Verma, Department of Physics, S.L.I.E.T.


As we know today our world is running on computers wherever we see aside us there is something related with computers or in easy words our life has become dependent on computers and they are playing a major role in our lives. After COVID there is a rapid increase in the use of computers in our lives. Firstly, when computers were started to be designed, they were big machines which consisted of chains and pulleys. Much time is taken to operate them. As we get advance Scientists and Engineers make changes in the computers. From the first computer to Supercomputers the world has changed and now we are going from those supercomputers which are termed as classical computers now we are trying to go on quantum computers.   

Classical Computers

If we try to define Computer it can be defined as “An operating or an electronic device which is used to manipulate the information, store data and which can be used particularly in education and research”. This is a definition every student who studies computers has learned, It is the most basic definition of a computer. Classical means old like the term we used for classical music but this classical is not as old our term classical means here the computers which are not working on the ideas of quantum computing. We know the father of computers was Charles Babbage who invented the first programmable computer from him. The revolutions in the computer had started whereas in the field of computers the first computer is known as abacus, a calculator type machine. Charles Babbage who made the first computer doesn’t make the computer which we are using today, these are known as digital computers, he made the computers which were big machines work with pulleys as discussed earlier. After those computers many changes has been made in the computers that  a machine is made which is known as electro mechanical calculating machine were made which was also a computer an advance version of Charles Babbage’s machine, now since they are not easy to operate time consumption and many more disadvantages leads scientists to enhance more and they form another computers named as Analog computers, which direct use electrical and mechanical model for the problem of computation but the problem was that they were not programmable. After that in the 20th century, during World War 2 digital computers were formed which were programmable. Time changes, we get more advanced and now we are in modern supercomputers. Modern computers are in our houses, hands like mobile phones, calculators, laptops, etc. Supercomputers are not with the normal person they are with the companies like Google, IBM, Microsoft and many bigger companies. The fastest supercomputer is made by IBM known as Summit which is very fast. These supercomputers can store roughly 9 petabytes of data that is a much higher value.

A Journey from Classical to Quantum Computers
Figure 1: Supercomputer of IBM named Summit

Approach towards Quantum computers

The population is directly proportional to the data, As there is increase in the population of world there is increase in data so now the problem is where to store that data because to store that data any platform is needed for example that we all use Instagram and many other applications we are uploading posts on it so to display it has to be stored somewhere and it is stored by the application similarly like you billions of persons are uploading and consuming data but there is a limit to increase that limit people are working so more data can be stored, but there is a problem that to make more storage supercomputers are getting heated up and consuming more space so it is becoming difficult for the companies. Second, calculations of problems, nowadays problems are becoming much heavier and larger to solve those the normal computers or supercomputers are taking a lot of time like thousands of years to solve the problems but it is assumed or the statement of Google who uses the term quantum supremacy and tell that the problem which a supercomputer can solve in 10000 years quantum computer can solve it in seconds but this statement was contradicted by IBM that their supercomputer SUMMIT can solve it in 2.5 days. But after a few years, the University of China came with a computer that was solving the extremely bigger problems in seconds that were taking years for supercomputers to solve. They were not completely settled up but were enough to work on functions of quantum computing methods. Now there came a term quantum supremacy but the question was the supremacy for what a thousand years or 2.5 days whatever it is quantum computers are making things way easier. After all these things started to happen, we came to a new extent that we need quantum computers on which now the whole world is working and we are thinking that one day there would be quantum computers in the world like we are using today. Personally, I don’t think that they will be in our hands, they will be like supercomputers that only we can access our data into.

Quantum Computers

A Journey from Classical to Quantum Computers
Figure 2: Quantum computer made by IBM

Quantum computers work on the phenomenon of quantum mechanics postulates. If we try to have a brief on quantum mechanics it is applied to very small quantities like to know the behaviour of electrons and other fundamental particles, even nuclear physics is completely explained with the help of quantum mechanics postulates. The basic difference between classical and quantum computers is that classical computers work on bits which give one state at a time like a switch but in quantum computers it can give many possible values at a single time which works on quantum bits named as qubits basically represented by Bloch sphere. Multiple qubits can give multiple values on the basis of probability. A qubit gives value like a wave function some part of it in 0 and some in 1, if we add up it adds up to 1, a complete value. If we try to understand the behaviour of quantum computers, we have to understand three concepts which are Superposition, Entanglement, and Interference. The term Superposition comes basically at lots of places in physics, here it means getting the desired value with the help of probability like for a qubit if we are getting 30% value of 0 then we will get 70% value of 1, means due to this property we can get two values for one qubit, and for 2 qubits there can be 4 states, for 3 qubits there can be 8 states and for n states then can have 2n values which is a very large number and up to thousands of qubits we can store the data of the whole universe. A qubit is an independent property of a quantum computer but due to Entanglement happening in those qubits they are inter connected with each other like if we talk about two qubits, they can combinations like 00, 01, 10, 11, if the probability of 00 will change other values will also get affected which is due to the property of entanglement that means that qubits interact with each other and effect on the values which after all can be taken as desired with the help of probability. A qubit is really described by a wave and we know that multiple waves in reality gives the resultant wave the property of interference, it is of two types constructive and destructive interference. Constructive interference means addition of two waves where the probability is high and destructive interference means subtraction of two waves where the probability is low, this is a process by which we get the desired result for a specific value or a desired value in a calculation. So, these are properties by which quantum computers run through to give the values or to calculate the values from equations. A quantum computer needs very low temp or a temp of absolute zero to run on which qubits can run through, they cannot work on room temp like a normal computer does. Till now we haven’t reached a complete quantum computer but our scientists and engineers are working hard to achieve this and it will be a complete revolution in the life of humans.