What is Quantum Computing?

Let's start!

Quantum computing is an area focused on developing computer technology based on the principles of quantum theory (which is the theoretical basis of modern physics that explains the behaviour of matter and energy on the atomic and subatomic levels.).
Quantum computers (like the one the article cover) aren't a more powerful version of our computers, not an improved version, instead, they are different just like bulbs aren't more powerful candles.

Important Key terms

Quantum : is the minimum amount of any physical entity (physical property) involved in an interaction.

Qubit : is the basic unit of information in quantum computing. So, it is the quantum mechanical analogue of a classical bit.

Quantum State : is a description of some physical system which is adequately detailed that it allows for a prediction of the system's behaviour in the near future according to the evolution equations. So, it is a lot like a classical state.

Quantum Entanglement : is the physical phenomenon that occurs when a group of particles share spatial proximity in a way such that the quantum state of each particle of the group can't be described independently of the state of the others, including when the particles are separated by a large distance.

Interference : is a phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude.

Superposition

It is the ability of a quantum system to be in multiple states at the same time until it is measured.
Much like waves in classical physics, any two (or more) quantum states can be added together and the result will be another quantum state. So, every quantum state can be represented as a sum of two or more other distinct states.

Do you know that in quantum physics a molecule can be excited and not excited at the same time? this might seem weird, but the way it is determined is by the energy level of that molecule.
So, if the energy level is above a certain level we will consider it excited. But when we measure it only one of the two states is observed randomly.

• The Time it takes for the superposition to disappear is called the decoherence time.

Models of Computation

"Models" here are just standard ways that were suggested by other scientists to build a quantum computing process for specific purposes.

Note : It is ok if you didn't fully understand what these models represent, as the most important thing in this section is to have a brief look at them.

The four relevant models of computation are :

• Quantum gate array – Computation decomposed into a sequence of few-qubit quantum gates.
  

• One-way Quantum Computer : Computation decomposed into a sequence of Bell state measurements and single-qubit quantum gates applied to a highly entangled initial state, using a technique called quantum gate teleportation.
  

• Adiabatic Quantum Computer : It is based on quantum annealing, and the Computation decomposed into a slow continuous transformation of an initial Hamiltonian into a final Hamiltonian, whose ground states contain the solution.
  

• Topological Quantum Computer : Computation decomposed into the braiding of anyons in a 2D lattice.

How Do Quantum Computers Work?

Quantum Computers perform calculations based on the probability of an object's state before it is measured - instead of just 1s or 0s - which means they have the potential to process exponentially more data compared to classical computers.
They carry out logical operations using the definite position of a physical state. Its operations are based on one of two positions. A single state - such as on or off, up or down, 1 or 0.
In quantum computing, operations instead use the quantum state of an object to produce what's known as a qubit. These states are the undefined properties of an object before they've been detected, such as the spin of an electron or the polarization of a photon.

Quantum Gates

Quantum Logic Gate (Quantum Gate) : is a basic quantum circuit operating on a small number of qubits. They are the building blocks of quantum circuits like classical logic gates for digital circuits.

Hadamard Gate

Circuit Representation of Hadamard Gate

It is one of the most important gates in quantum computing. It puts a qubit into a superposition of states.
So, when the qubit is measured it will collapse to either |0〉 or |1〉with equal probability.

Obstacles in Quantum Computing

One of the biggest obstacles in Quantum Computing is the "noise" problem.
In the quantum, ‘noise’ is not an undesirable sound. It is interference that can be caused by internal and external factors.

External factors : include magnetic fields, and variation in temperature.

Internal factors : indicates that the noise could be determined by the interactions between the qubits themselves, because of their entanglement (we explained it in a previous section ) and the fact they need to interact in order to perform computations.

Quantum Error Correction(QEC)

It is a way to protect quantum information from errors due to decoherence and other quantum noise.
The first quantum error-correcting codes were discovered independently by Shor, and Steane. Shor proved that 9 qubits could be used to protect a single qubit against general errors.
Quantum Decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition.

Why Do We Need Quantum Computers?

We need them because, for some problems, supercomputers aren’t that super.
Quantum Computers have the ability to make certain types of classically intractable problems solvable and simulate complex events in nature that require a huge exponential complexity on a classical computer.

Theoretically, the problems that a quantum computer solves are the same as classical computers can solve, but the main difference is the feasibility, efficiency, time complexity, and space complexity of the processing.

Some of the applications that we use quantum computers in are :

• Cybersecurity & Cryptography
• Artificial Intelligence & Machine Learning
• Computational Chemistry
• Financial Modelling

Quantum Computing Companies

• IBM
• Microsoft Azure Quantum
• D-Wave Systems
• Quantum Computing Inc. (QCI)

Prerequisites for Learning Quantum Computing:

• Basic quantum mechanics.
• Linear algebra.
• Basic group theory (and generally basic abstract algebra)
• Basic probability and stochastic processes.
• Fourier transforms.
• Basic algorithms and analysis of algorithms.

Qiskit

What is Qiskit?

It is an open-source software development kit for working with quantum computers at the level of circuits, algorithms,...etc.
It allows anyone to program on real quantum computers using only their laptops. It contains optimized C++ simulator backends for executing compiled circuits.

Algorithms

Qiskit contains a generic framework of cross-domain quantum algorithms upon which applications for near-term quantum computing can be built. Qiskit has a textbook that you can read from here.
And for sure if you want to start your journey in quantum computing then you should start learning Qiskit from the official website from here

Shor's Algorithm

It is an algorithm that runs on a quantum computer for integer factorization. It solves the following problem: Given an integer N, find its prime factors.
Shor’s algorithm is arguably the most dramatic example of how the paradigm of quantum computing changed the perception of which problems should be considered tractable. You can learn more about it from here.

Thank you, and goodbye.