Quantum Computing - How It Works(양자컴퓨터의 원리)

Famous IT companies like IBM, Google, Intel, ....etc are jumping into making quantum computers, and are making some success. But then, what are quantum computers and why are they so important? In this page, I am going to explain qubit-based quantum computers.

https://crypviz.io/knowledge-database/quantum-resistance/qubit/

A normal computer calculates and stores data using a system called 'bits'. A bit can be either on or off, or in numbers, 1 or 0. An n-bit computing system can only store an 'n' amount of information: each bit as 0 or 1 representing an information. On the other hand, a quantum computer can deal with much more information. Since the exact state of a qubit cannot be identified before being seen and is in a superposition, it can be thought to have all possible 'bit codes' at once. In order to represent the state of the qubit, its possibillities will each be given a coefficient. Since an n-qubit system will require 2^n number of coefficients, so is the number of information it can compute.

 

n-bit/qubit system

ordinary computers: n data

quantum computers: 2^n data

http://propg.ufabc.edu.br

How is information of a qubit detected? Scientists use the spin states of electrons(or nucleus) to do so. In low energy conditions, an electron will always have a down spin. This is considered as '0'. Since even the thermal energy of room temperature can change its spin, qubits in a quantum computer have to be kept in very cool conditions(this is why quantum computers have to be cold). When a long-pulsed electromagnetic wave hits the electron, it absorbs the energy and turns into a spin up state(1). This change in an electron can be dectected because a spin up electron has a higher energy than other electrons. For a nucleus-qubit system, the atom's elcetrons' spin state cannot be changed when the spin state of the nucleus is up. This characteristic enables us to dectect the spin of a nucleus-qubit. Qubits based on electrons are more simple, while those based on nuclei last longer.

 

Quantum computing can be used to compute an enormous length of calculation. It reduces the number of calculations to be made in the process of solving a problem. However, in most cases(that do not include complicated calculations), it will not give any outstanding advantage over ordinary computers.