# A Brief Quantum Computing Introductory

As a first kick-off of a prospected journey of learning on Medium, quantum computing intro is somewhat a fascinating topic to discuss.

A Path to Quantum Computing

A possible quantum computation thought firstly stated back in 1959 by an American Physicist Richard Feynman. He proposed an idea where quantum mechanics effects can have a direct impact on computer technology and application. Many researchers were also striving to retrieve the use of popular modern physics phenomena called superposition to be employed in computer development.

There has been a number of experiments done by experts worldwide especially in 90s where quantum computer theory had been enhanced. A quantum logic gates construction for a universal quantum computer was elaborated by David Deutsch from the University of Oxford in 1985. Nearly ten years later, an algorithm of six qubits quantum computer for number factoring was mapped out by Peter Shor of AT&T.

The fundamental experiments continued until late 90s when several promising trials were successfully conducted by Isaac Chuang (Los Alamos National Laboratory) and Neil Gershenfeld (Massachusetts Institute of Technology). They managed to build 2-qubit quantum computer by dissolving chloroform molecules (CHCL3) at room temperature and orient the carbon spins and hydrogen nuclei by applying external magnetic field.

Definition

Quantum computer can be gently said as next-level computing technology which utilizes the effects of quantum mechanics instead of classical electronic binary system. Basically, the concept of quantum computing is to harness the so-called strange effect of superposition for computation.

Quantum Bit

Classical computer uses (binary) bit as representation of digital system inside computer and a fundamental concept to explain how computation is performed. So as the classical one, quantum computer has its own concept in deliberating computation: quantum bit (qubit).

Unlike classical binary bit where there can only be one state either 1 or 0 at a time, qubit, theoretically, can be in two different states, denoted with |0> and |1> at the same time, written in Dirac Notation which corresponds to state of 0 and 1 in classical binary system. This phenomenon is commonly known as linear combinations of states, or superpositions, expressed by following mathematical equation:

| ψ> = α|0> + β|1>

Quantum Information

Quantum information can generally be classified into two manners in term of discussion about it. The first one is wide understanding covering the whole usage of quantum information in the scope of quantum computation, quantum teleportation, and the no-cloning theorem. The second one encompasses more specific utilization of quantum information term which refers to the analysis of elementary quantum information processing tasks.

Regardless, quantum information can be simply interpreted as unifying element that gathers three fundamental scientific works;

a. Elementary classes identification of constant resources in quantum mechanics.

b. Elementary classes identification of dynamic process in quantum mechanics.

c. Study of resources calculation for noisy communication channel employed for quantum element transfer.

Fundamental Scientific Background

As it is known that in the quantum theory, one particle or object is not necessarily obliged to be in one particular state, instead, it can be in any of two states. Quantum mechanics, theoretical physics, and in-depth knowledge of linear algebra are obviously foundations of gate to quantum computing. However, multidiscipline conception relied on those fields is practically more reliable for someone to grasp the scientific idea of quantum computing.

Even though semiconductors-based quantum computational system is not yet possible, some radical experimentations are carried out to ensure that the concept and the realization of quantum computing are aligned.

As mentioned in the previous points, one of the most fundamental scientific quantum computing related experimentations was performed by Isaac C, Neil G., and Mark K., by conducting physical manipulation of chemical reaction of chloroform molecules (CHCL3) in 90s. This lab work was then resulting to the known first 2-qubit quantum computer which is capable enough to proceed with the data loading and generating a solution. They managed to practically implement quantum process idea to nanosecond coherence quantum entanglement, despite its incapability to compute meaningful task. Many are considering subatomic level process is the only way to realize quantum computing, they instead went with chemical approach where they created chloroform molecules solution in room temperature water then changed the spin orientation of the isotope carbon-13 and hydrogen nuclei using magnetic field. The generated parallel spin to the given magnetic field was considered as a 1 and the opposite or antiparallel spin as 0, while the carbon isotope and hydrogen nuclei was interpreted as a 2-qubit system.

Working Principal

Quantum Computation

The so-called language of quantum computation is meant to describe the process in quantum computing. This concept is basically saying that, instead of employing electrical circuit built up from IC logic gates, a quantum computer performs computation using quantum circuit containing quantum gates to proceed with the information and tasks.

There are two essential approaches or modelling of how quantum computer can process computational steps and logics in solving particular level of problem using its register of qubits: the quantum Turing machine and the quantum circuit model.

Quantum circuit is basically understood as quantum gates replacing classical circuit in the position of digital gates AND, OR, and NOT. Technically, quantum circuit consist of some sequence of quantum gates. Some of the examples are bitflip gate X, the phaseflip gate Z, the Hadamard gate H, with one of the most common one in 2-qubit operation is controlled-NOT (CNOT). Those interpretations of quantum gates are employed in the information quantum computing process differently with classical gate arrays which composes only certain static digital state in standard basis vector, unlike superpositions. The aforementioned quantum gates, through with noisy communication channel are performing computation which gives more dynamics possible quantum state parallelly. Therefore, from the above concept, quantum Turing machine is explained as a computational system utilizing quantum circuit in solving numerical and logical tasks analogously with the classical Turing machine.

Quantum Algorithm

Quantum algorithms often takes analogy from classical algorithm where it actually composes superpositions for the sequential processing in the level of digital gate arrays of classical computer. In the early stage of its development, quantum computing is expected to solve problems or tasks that conventional computer with classical sequential process cannot do so, or, in more practical term, to output solution in extreme gap of faster time. One of the wide known problem that was designed specifically for quantum computing is Deutsch — Jozsa problem by David Deutsch and Richard Josza in 1992. The Deutsch — Jozsa function is made to output either 1 or 0 for n-bits (qubits in this case) constantly (1 or 0 for all input) or in balance (1 for half input and 0 for the rest half). A further development of this function specially made to surpass conventional computer using “unknown” system and condition to output desired result without any error and with super high accuracy is then known as Deutsch Algorithm.

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Motivation

The reasons why quantum computing is studied may vary. However, based on the capability which quantum computer possess, at least there are three main objectives why quantum computer is widely researched:

a. Atomic Level Computation

The application of quantum mechanic brings inevitable quantum effects in technological basis.

b. Speed

As experimentally proven, quantum computing promises extremely higher speed than the classical one, not only in term of computation but also for example in crypto-related purpose application.

c. Nature-based Technology

One objective that many scientists are attracted to is having understanding of the most powerful nature-based computing devices.

Researches and Applications

The nearly endless possibilities that quantum computing possess has put together bright minded scientists and engineers around the planet to pave an unprecedented way of computing.

The recent activities of quantum computer development have promised breakthrough that encompass the pass researches, such as the creation of quantum computer by IBM which is capable to perform computation in seconds whereas modern supercomputer needs decades to complete.

The more fundamental and principal researches on quantum physics and subatomic electronic have also pushed new possibilities in realization of quantum computing, making future definition way ahead. One very recent breakthrough of which is an experiment dedicated to manipulate quantum registers have successfully made it to accomplish designated wavelength. The experimental research that has been published in Nature used Silicon Carbide to interface quantum register with photons, opening a possibility of remote communication of quantum information, simply saying, “wireless” quantum information transfer.

By what quantum computing brings, if things go as expected, warm hole simulation, inter galaxy travel analysis, climate change solution projection, with excellent accuracy and least error, all will be done in a blink.

References

[1] Yanofsky Noson. An introduction to Quantum Computing. Researchgate Publication №1758552, 2007, c. 2–3.

[2] Britannica Online Encyclopedia. Quantum Computer. Available at: https://www.britannica.com/technology/quantum-computer , accessed October 7, 2020.

[3] Leverrier, Anthony, et al. Introduction to Quantum Computing. Lecture Notes of IQUPS Course. 2018.

[4] Beneti, Giuliano, et al. Principles of Quantum Computation and Information Vol. 1. World Scientific Publishing, Singapore, 2005, c. 1–2.

[5] Wolf, Ronald de. Quantum Computing : Lecture Notes. QuSoft, CWI, and University of Amsterdam, 2019, p. 13–18.

[6] Nielsen, Michael A., et al. Quantum Computation and Quantum Information. Cambridge University Press, Cambridge, 2010, p. 27–29.

[7] Rieffel, Eleanor, et al. Quantum Computing: A Gentle Introduction. The MIT Press, Massachusetts, 2011, p. 123–125.

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