Gordon Moore, the founder of Fairchild Semiconductor and former CEO of Intel in his 1965 paper, described that the number of transistors in a dense integrated circuit double about every two years and this statement is famously known as Moore's Law. Moore's law was consistent for the past 50 years, but with the current technological advancements, it is coming to an end. It is starting to become physically impossible to reduce transistor sizes to increase computational efficiency further, and hence this calls for alternate methods.
One of the major areas of research is the development of quantum computers. A Quantum computer utilises quantum mechanics to perform a computational task that is governed by entirely different rules and should not be mistaken as an upgrade to the current classical computers. It promises to solve problems which are currently out of our reach. The quantum realm opens up a compelling alternative to classical computers in the form of quantum computing, which utilises Quantum mechanical phenomena such as superposition and entanglement.
The race to build the first quantum computer that can help scientists to find cures for diseases, to encrypt data with perfect security, and predict the earth's climate changes is well underway. Quantum computers could very well be the next big thing in the tech landscape, with a majority of industry leaders investing heavily in it and not making the same mistakes that were committed when the computer was first introduced. These include companies such as IonQ, Rigetti, IBM, Google, Alibaba, Microsoft, Intel, who are spending billions of dollars on quantum computing development and research.
The most fundamental difference between quantum and classical computer is:
Classical computers utilize the classical phenomenon of electrical circuits(logic gates) being in a single state at a given time, either ON or OFF. Consider an ordinary coin, the two sides of the coin represent the two states, for example - heads represent ON(bit 1) and tails represent OFF(bit 0) or vice versa. Hence at a given moment, the coin is either heads or tails, i.e. one bit can store either 1 or 0.
Quantum computers utilize quantum mechanical phenomena specifically superposition, which is the phenomenon in which it is possible to be in more than one state at a time. Consider the same coin, on spinning the coin it is observed that the coin is in a superposition of states, both heads and tails, i.e. both 0 and 1 and on stopping the coin for measurement it is either a 1 or a 0. Therefore quantum bits(Qubits) can exist in multiple states at the same time until measured and can effectively hold 2 bits of data. There are different possible physical implementations of Qubits like polarisation of a photon, spin states of an electron, etc.
The Need For Quantum Computers
Since a Qubit can effectively hold two bits of data rather than one, quantum computers can dramatically increase computational power. However, it may prove beneficial only to certain types of problems, and the main research interest is in identifying these problems and developing algorithms for them.
Classical computers find it difficult to carry out functions that have exponential growth, such an example is Prime Factorization of large numbers, which would take countless years for classical computers to factor them. In contrast, by utilizing Shor's algorithm, which is based on Quantum mechanical principles, this task is completed in seconds.
Quantum computers will have a massive impact on data security. Even though quantum computers would easily crack many of the encryption techniques today, predictions are that they would create hack-proof replacements. Other applications where quantum computing can make an impact are molecular modelling, mathematical optimisations, machine learning and much more.
There are challenges at every level of a quantum computing system, from assembling qubits to reading and writing information on them, to sending data back and forth without it disappearing. Qubits are challenging to manufacture and should be maintained at temperatures lower than outer space.
Decoherence is a phenomenon which reverts a quantum system to a classical system through interactions with the environment which decay and eliminate quantum behaviour of particles, and this poses as a major disadvantage. Due to decoherence, qubits can lose its quantum properties and superposition to the slightest of vibrations from nearby atoms, making it highly sensitive. Radiation, light, sound, vibrations, heat, magnetic fields or even the act of measuring a qubit are all examples of decoherence.
In quantum computing, quantum supremacy is the goal of demonstrating that a programmable quantum device can solve a problem that classical computers practically cannot.
Google has announced that its 54-qubit Sycamore processor was able to perform a computational task in 200 seconds that would have taken the world's most powerful supercomputer 10,000 years. IBM, which operates the supercomputer that Google claims to have beaten is disputing their claims. IBM has responded by stating that the random number problem that the quantum computer solved takes less than three days on its supercomputer rather than 10,000 years, and thereby are arguing over the legitimacy of the claim, as the random number problem was not out of the reach of classical computers.
A popular misconception about Quantum computing is that it is going to replace classical computing. Quantum computers will not fully replace classical computers. They will offer a fundamentally different way of performing calculations and will be able to perform tasks that would take classical computers millions of years to compute. While it is true that Quantum computers have the upper hand in specific problems like the simulation of biological molecules, factoring large numbers, etc., it fails to perform effectively on others, mainly because scientists have only developed a handful of quantum algorithms.
The most likely scenario is that both Quantum computers and classical computers coexist, with the quantum system present as an add-on to tackle harder problems.
Quantum computers are in its infant stage at present—the situation is very similar to how classical computers started, where computers were mainly used by scientists and not much user-friendly for others. It took time and technological advancements to improve on the usability and to teach people how to use computers, quantum computers will also follow through the same pipeline and pave the way to a technologically brighter future.