# Principles that Distinguishes Quantum Computing from Classical Computing — Simple Guide

Have you ever wondered about the buzz around quantum computing and how it’s different from the classical computing we’re all familiar with? We will discuss some important principles in this article that make Quantum Computing Distinct in itself.

# Introduction:

After the advancement of classical computing, we are moving towards an exciting new horizon of quantum computers and these Quantum Computers work on the principles of Quantum Physics.

Before going deep into this we will first discuss some things about Classical Physics.

# A little About Classical Physics:

If we talk about classical physics it classifies entities either as particles or waves. Particles are considered to be localized in space, meaning they have a specific position at any given time and you can determine the location of a particle with a high degree of precision. Waves are spread out in space as they do not have a specific location but rather exist across various points. For example, a wave in water is not located at a single point but rather is spread out across the surface. These particles and waves cannot be exhibited by a single entity.

One of the reasons for the distinction between quantum physics and classical physics is due to the dual nature of light. Classical physics is not able to define the dual nature of light, which exhibits both wave-like and particle-like behavior. This duality is also observed in other subatomic particles such as electrons and protons. Quantum mechanics provides a more complete description of the behavior of these entities, including the wave-particle duality of light.

## - Double Slit Experiment:

The double-slit experiment is a classic experiment that demonstrates this duality. When the electrons are fired one at a time, they behave like particles and create a pattern of discrete dots on the screen. However, when electrons are fired through two slits, they form an interference pattern on the screen, which is characteristic of waves.

# Why Need Quantum Computing?

Intel co-founder Gordon Moore predicted that we would be able to double the power of the computer every two years and this prediction is known as **Moore’s Law**. According to him, we would be able to do this by increasing the number of transistors on a chip.

This law worked well, but now it seems to be failing because reducing the size of a transistor was the one method to increase the power of the computer but as these transistors get smaller and smaller, the quantum effect like quantum tunneling causes problems.

# Differentiating Principles:

Now we will discuss some general principles that distinguish Quantum Computing from Classical Computing:

## 1) Qubits:

In classical computing, we represent the information using either 0 or 1 bits. The device computes by manipulating these bits with the help of logical gates (AND, OR, NOT).

In quantum computing, a qubit or quantum bit is the basic unit of quantum information. A qubit can be in states of 0 and 1, but it can also be in a superposition of these states meaning something like a mixture of 0 and 1. This means a qubit can hold a one, a zero, or crucially a superposition of these values. The device computes by manipulating these bits with the help of quantum logic gates.

Following are three different representations of qubits:

## 2) Superposition:

Currently, classical computers are accustomed to using bits. Superposition is the ability of a quantum object to be in multiple states at the same time, with probabilities of being measured in each state. Having the qubits in superposition in quantum computing makes it easier to solve permutation problems and it is extremely useful not only to crack encryptions but also to secure encryption channel generation using **Quantum Key Distribution**.

The concept of superposition in quantum mechanics is central to the experiment of Schrödinger’s cat.

You can read more about Schrödinger’s thought experiment here:

## 3) Interference:

In quantum mechanics, when a particle is in a superposition of multiple states, these states can interfere with each other, leading to constructive or destructive interference. Constructive interference occurs when two in-phase waves peak at the same time, resulting in a wave that peaks twice as high. Destructive interference occurs when two out-of-phase waves peak at opposite times, resulting in a completely flat wave.

This interference is used to affect probability amplitudes. Each possible outcome of a quantum computation has some probability of occurring, and interference can amplify certain outcomes and suppress others. This is achieved by applying quantum gates that create superpositions of qubits and by controlling the relative phases of the states.

For example, Grover’s Algorithm which is a quantum search algorithm, uses interference to perform high-speed searching on unstructured data.

## 4) Entanglement:

Two quantum objects are said to be entangled when one object’s state depends on another object’s state. When these two objects are entangled, they have a defined relationship, so if you know one object’s state, you know something about the other state. This principle holds still even when these objects are separated by far distances.

Quantum Entanglement allows us to store and find information more powerfully than it is possible with classical objects. For now, entanglement is also being used to implement quantum internet.

## 5) Measurement:

Measurement is the process of forcing a superposition to pick what state the object will be in and it gives either 0 or 1. This is an irreversible process and destroys the superposition.

This collapse of the superposition can be understood using Schrödinger’s experiment in which when a cat is in the radioactive box, we do not know whether it is alive or dead (superposition), and we only know the real outcome when it box is opened.

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