Quantum Computing : Basics

Starting from the year 1946, when the first digital computer of the world was completed, computers have changed the way we live our lives. Computers have given the world  some pretty amazing things including space travel, flying, operate internet,  autonomous vehicles, artificial intelligence, robotics, weapons of mass destruction, health care and communications to just name a few. Classical computers do this by computations based on the binary digit or  bit i.e. 0 & 1.

The computing capability of a smart phone of today far exceeds that of the computers which used to occupy a building and were exclusively being used by the armed forces in USA and erstwhile USSR in the 1950s. This has been made possible primarily because of the ‘ transistor ’, arguably the most remarkable application of quantum mechanics. The computational power mentioned above is nothing but the number of floating - point operations per second (flops) that a computer can perform. While in the 1950s we were using vacuum tubes which could perform about 1000 flops, we now have super computers capable of performing peta flops i.e. 10¹⁵ flops, this remarkable feat is owed to miniaturisation. The famous and still applicable Moore’s  Law explains this. In the 1960s, Intel co-founder Gordon Moore realized that the power of computers doubles roughly 18 months. This was because of number of transistors that may be placed on a single integrated circuit chip doubles approximately every 18 - 24 months. Extrapolation of Moore’s law suggests that by the year 2020 we would be reaching atomic size to store a single bit of information, at which stage quantum effects would take over.

Despite their formidable computing prowess there are still certain issues with the conventional computers two of which explained in layman’s terms.

Optimisation. This is nothing but finding the best possible solution amongst a number of possible solutions. Let us examine a simple scenario. In an officer's mess, ten people are to be seated around a dining table, how many ways can this be done ?  Simple answer, it would be 10 factorial, which is 3.6 million ways ! Now if one was to increase the No. of guests, the rise in the possible seating configuration would be exponential. Classical computers can handle small versions of such problems but struggle to handle the larger ones.

Exponential Scaling. This is also best explained using an e.g. of the famous chess board fable If a chessboard were to have wheat placed upon each square such that one grain were placed on the first square, two on the second, four on the third, and so on (doubling the number of grains on each subsequent square), how many grains of wheat would be on the chessboard at the finish ? The total number of grains equals 18, 446, 744 ,073, 709, 551, 615 ! This is how quickly the exponential sequences grow and classic computers cannot handle that.

To handle such issues, quantum computing offers the possibility of computing capability millions of times more powerful than current systems using parallel instead of sequential process !

What is Quantum Computing?

Qubits. Rather than storing information using bits represented by 0s or 1s as classical computers do, quantum computers use quantum bits, or qubits, to encode information as 0s, 1s, or both at the same time. This is called Superposition. There are some other properties too of quantum information,  these are discussed below.

Quantum Superposition. Without dwelling into the mathematical concepts one can understand this as a coin toss. A coin toss can result in either heads or tails but while the coin is in the air and flipping it can result in both heads and tails ; this is nothing but superposition. Qubits use superposition to represent multiple states (multiple numeric values) simultaneously in a similar way.

Quantum Entanglement.This occurs when two or more qubits are entangled, then measurements of physical properties such as position, momentum, spin, and polarization, performed on entangled particles are found to be correlated.

Quantum Algorithm.This term is used for those algorithms that incorporate some essential feature of quantum computation such as quantum superposition or quantum entanglement discussed above. Shor's algorithm for factoring and Grover's algorithm for searching an unstructured database or an unordered list are the most well known examples of the same.

How to Build Quantum Computers

Theoretically, quantum computers are buildable however in practice there are number of issues which are yet to be tackled in a manner to make these machines viable. Some of the obstacles include storage of qubits, ease of reading qubits, cooling requirements and reduction of error rates.

Will it Happen. Yes it would ! This seems to be the message from all computing giants of the world. However, this may take decades as some critics point out that quantum computers are yet to beat classical computers on even one task !

Conclusion

It has been over three decades now since this idea took roots, however quantum computers remain elusive on ground. Notwithstanding the obstacles, there are scientists who are convinced that quantum computing is the future and breakthroughs are being made all the time and yet it may be even decades to go before a viable quantum computer is realised.