“We are soon going to get the world’s most powerful Quantum Computer”, Well…headlines like this about the Quantum computers have become quite common these days. When Charles Babbage conceived the idea of programmable computers in the 19th century, who knew, that one day this quirky device would become a part and parcel of our daily life. The computers have completely invaded our lives in the form of cell phones, tabs, desktops, laptops and a lot more. If you came across this article, then definitely you are also hooked up on one such device right now! Isn’t it?

ENIAC, World's First Computer, 1946
ENIAC, World’s First Computer, 1946

However, all these gadgets come under the category of Classical computers. As we know, these are pretty good and efficient to perform all the major operations that we come across in our day to day life. Then, why is there a need to have something called Quantum Computers, and how are they different from the classical computers that we use? Let’s find out!

The Need for Quantum Computers :

Undoubtedly, We experience the benefits of classical computing every single day. However, there still remain some challenges that today’s classical systems will never be able to solve. When it comes to the problems that surpass a certain size and complexity, we don’t have enough computational power on Earth to tackle them. To stand a chance at solving some of these multiplex problems, we need a new kind of computing. And, this is where the idea of Quantum Computers comes into the frame!

Working of Quantum Computers versus the Classical Computers:

Postulated by Deutsch in the 1970s, Quantum Computers have now become a talk of the town. All the computing devices in this universe rely on a very basic ability to store and manipulate information. The classical computers manipulate individual bits and store information as binary 0 and 1 states. However, the Quantum computers on the other hand employ quantum mechanical phenomenons to process the information. So, where classical computers use classical logic gates to do the computation, the quantum computers engage quantum logic gates to achieve this. And, in order to do this, they rely on quantum bits, or qubits.

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The Qubits represent the undefined properties of an object before they’ve been actually measured, such as the spin of an electron which is uncertain before any measurement takes place on it. In other words, these quantum bits represent a state of superposition. So, for a single bit system, where classical computers can store information in either binary 1 or 0, the quantum computers can also utilize the superposition of 0 and 1 to achieve the same more efficiently. But there is more to information processing in quantum computers than just superposition.

Superposition of Spin up and spin down
Superposition of Spin up and spin down
Image Courtesy:abyss.uoregon.edu

If we look at a system of more than one qubit, then the individual components aren’t generally independent of each other. Instead, they can be entangled. This means that when you measure one of the qubits in an entangled system of two qubits, then the outcome immediately tells you what you will see when you measure the other qubit. Moreover, the particles can be entangled even if they are separated in space. This magical property of entanglement forced Einstein to call entanglement “spooky action at a distance”. Both these Quantum phenomenons of superposition and entanglement are the backbone of Quantum computers.

An example of entangled pair that can be used in Quantum Computers
An example of entangled pair that can be used in Quantum Computers
Image Courtesy:Wikipedia

Quantum Computers in the Real World:

The idea of Quantum Computing is really very fascinating, but equally complex to implement in the real world. The Qubits are the building block of a Quantum Computer. So, in order to build a Quantum computer, the first task is to generate Qubits. There are a few different ways to create a qubit. Generally, those things that can live in superposition can be used as Qubits. This involves the use of atoms, ions, electrons, photons etc. to act as Qubits in the real world.

Quantum computer based on superconducting qubits developed by IBM Research in Zürich, Switzerland.
Quantum computer based on superconducting qubits developed by IBM Research in Zürich, Switzerland.
Image Courtesy:Wikipedia

Maintaining a quantum state for longer time is another major challenge to face in the real world Quantum computing. One of the known method uses superconductivity to create and maintain a quantum state. To work with these superconducting qubits for extended periods of time, they must be kept very cold. Any heat in the system can introduce error, which is why quantum computers operate at temperatures close to absolute zero, colder than the vacuum of space.

How are Quantum computers superior to classical ones?

In 1997, the world’s first tiny quantum computer was built. Today, many players are engaged in this battle to build the most powerful quantum computer. These include some known commercial entities like IBM, Google, Alibaba, Microsoft , Intel, and a lot more, all willing to spend billions of dollars on quantum computing development and research. But, why to spend so much on these Quantum Computers. The answer is simple : because of their superiority over the classical computers in different contexts!

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Since Quantum computers perform calculations based on the probability of an object’s state before it is measured – instead of just 1s or 0s, they have the potential to process exponentially more data compared to classical computers. An n-bit classical computer can store only n amplitudes of information. Whereas, a n-qubit quantum computer can store 2^n amplitudes of information. This means that a 500 Qubits quantum computer can store more amplitudes than our estimate of number of atoms in the Universe! Baffled?… Wait! There’s even more to wonder!

Their speed is yet another mind boggling thing. For example, to break a widely used RSA 2048-bit encryption, a classical computer with one trillion operations per second would need around 300 trillion years. Whereas, A quantum computer using Shor’s algorithm could achieve the same feat in just 10 seconds, with a modest 1 million operations per second. Yes, That’s the power of quantum computers: 300 trillion years versus 10 seconds. In 1965, Gordon Moore extrapolated that computing would dramatically increase in power, and decrease in relative cost and size. And this is definitely proving out to be true!

Moore's law in practical form
Moore’s law in practical form
Image Courtesy: University of Delaware

Undoubtedly, Quantum computers can spur the development of new breakthroughs in various fields, be it security systems, finance management, research, medications and a lot more. But these are not very useful as far as our daily tasks of watching Netflix, writing an email etc. are concerned. These are not the places where quantum computers will really help you. But, even when the first classical computers were built, people had the same impression about them being useful only to scientists, and the rest you know. So, only the time will tell what the Quantum computers have in store for us!

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9 thoughts on “The Difference Between Classical And Quantum Computers”

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  4. Hi Simran, nice article,
    but like all articles dealing with quantum computing it does not explain why/how spin superposition is the way it is, nor why entanglement is the way it is (other than to call it a “magical” property ) This description has been missing from quantum mechanics, and although it is not strictly necessary for the physicist to have any such description, nevertheless, from the point of view of just about everyone else, such a graspable view is highly desirable.
    So I have put one together in a way that is easy and simple to understand while staying true to the Bell test, spin, entanglement experiments, showing why they are the way they are. And how classical and quantum are not at odds with each other but are in fact two different sides of the same coin. If you would like to have a look at it just for fun, the web address is https://easyquantum.net
    go visit leave a comment 🙂

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