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**Quantum computing is believed by many researchers to be the next step forward in information technology, and the exponentially more powerful processing ability that quantum computing promises could usher in a complete revolution in human understanding, lifestyles and relationships with technology and the rest of the planet.**

## Quantum Computing Basics

Quantum computing replace the binary units (bits) of classical computing with quantum bits (qubits). Bits – the building block of information technology – are states of either on or off, one or zero, and are assembled as transistors made of semiconductor materials in their hundreds and thousands. They are programmed using binary logic to use electronic signals to these transistors and complete the vast array of processing tasks (creating outputs from inputs) which modern society is absolutely reliant upon.

In short, qubits are states of on and off simultaneously. They are assembled as arrays of atoms (material in its quantum, smallest possible scale) in their twos and fifties, as scientists are as yet unable to control a larger array. No single method for producing a qubit has ascended yet, but researchers are experimenting with various approaches utilizing magnetism, trapped electrons, trapped atoms, nuclear magnetic resonance, linear optics and many more.

Due to their ability to occupy on and off states simultaneously (and other counterintuitive features of quantum physics such as quantum entanglement, where one atom can respond to a stimulus on another atom with which it has become entangled, regardless of the distance in time and space between them), qubits promise to be able to process information (inputs) usefully (giving outputs) at an exponentially faster rate than bits can.

## The Quantum Supremacy

This power is still, as yet, theoretical. Quantum supremacy – the proposed future state of quantum computing in which a quantum computer would be able to complete any task better than a classical electric computer – is the research goal of many working in the field.

For this reason, the purpose of most physical quantum computers produced so far has been to demonstrate or test quantum computing’s theoretical possibility. Meanwhile, theoretical quantum computers can be said to exist (if only on paper) as well. As well as physical and theoretical quantum computers, researchers have also developed simulations of quantum computing by programming classical computers to simulate quantum effects.

## The Advent of Quantum Computers

The first quantum computer was invented in the abstract in 1959, when physicist Richard Feynman delivered his seminal lecture, “There’s Plenty of Room at the Bottom”, to the American Physical Society at Caltech. In this lecture, Feynman proposed a number of new possibilities from the manipulation of matter on its atomic scale (its smallest possible interactive scale, i.e., its quantum scale), including the ability to produce denser computing circuitry (Feynman, 1992).

After Feynman’s lecture, the theoretical field of quantum computing did not progress far for two decades. However in 1980 American physicist Paul Benioff described a mechanical model for a quantum computer, and the next year Feynman again encouraged researchers to build a physical quantum computer in a keynote lecture at MIT (Feynman, 1982), but warned, “By golly, it’s a wonderful problem because it doesn’t look so easy” (Gil, 2016).

In 1985, British physicist David Deutsch theorized the first universal quantum computer – a quantum computer that could simulate any other quantum computer as could the universal Turing machine simulate classical computers. Theoretical quantum computers continued to be described throughout the 1980s and 1990s, and significant advances in quantum information theory – such as Peter Shor’s eponymous Shor’s algorithm, presented in 1995, which showed how quantum computing could factorize large integers that classical computers could never attempt – continued to progress the field.

These abstract quantum computers were used to continue to advance the field of research, bringing scientists ever closer to quantum supremacy. Key to the realization of a functional, universal, physical quantum computer was another theoretical framework proposed in the late 1990s by American theoretical physicist David DiVincenzo. The framework established the minimum requirements for building a physical quantum computer (DiVincenzo, 2000).

Finally, in 1998 a physical quantum computer was able to demonstrate processing a quantum algorithm – the first successful experiment, and concrete proof, of theoretical or abstract quantum computing’s possibility. Oxford University physicists Jonathan Jones and Michel Mosca, and soon after IBM researcher Issac Chuang with colleagues at the University of California, Berkeley, Stanford University and MIT used nuclear magnetic resonance to create an array of two qubits in a working quantum computer which was able to solve the Deutsch-Jozsa algorithm (designed specifically to be hard for a classical computer to solve, but easy for a quantum computer) (Chuang, Gershenfeld and Kubinec, 1998).

## Summary

Since then, physical quantum computer have grown to include over fifty qubits, and are coming ever closer to the state of quantum supremacy. Simulations of quantum computers programmed within classical computers have added to the physical and theoretical computers first developed in the field, and new advances in the field continue to make quantum computing more realizable and practical every year.

## Sources

- Benioff, P. (1980). The computer as a physical system: A microscopic quantum mechanical Hamiltonian model of computers as represented by Turing machines. Journal of Statistical Physics, 22(5), pp.563–591.
- Chuang, I.L., Gershenfeld, N. and Kubinec, M. (1998). Experimental Implementation of Fast Quantum Searching.
*Physical Review Letters*, 80(15), pp.3408–3411.
- Deutsch, D. (1985). Quantum Theory, the Church-Turing Principle and the Universal Quantum Computer.
*Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences*, 400(1818), pp.97–117.
- DiVincenzo, D.P. (2000). The Physical Implementation of Quantum Computation.
*Fortschritte der Physik*, 48(9–11), pp.771–783.
- Feynman, R. P. (1982). Simulating physics with computers.
*International journal of theoretical physics*, 21(6-7), 467-488.
- Feynman, R.P. (1992). There’s plenty of room at the bottom [data storage].
*Journal of Microelectromechanical Systems*, 1(1), pp.60–66.
- Gil, D. (2016).
*The Dawn of Quantum Computing is Upon Us*. [online] IBM THINK Blog. Available at: https://www.ibm.com/blogs/think/2016/05/the-quantum-age-of-computing-is-here/ [Accessed 27 Aug. 2019].
- Shor, P.W. (1995). Algorithms for quantum computation: discrete logarithms and factoring.
*Proceedings 35th Annual Symposium on Foundations of Computer Science*.

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